Non-aqueous electrolyte energy storage element

Abstract

A nonaqueous electrolyte power storage element according to an aspect of the present invention comprises a negative electrode having a negative electrode active material layer containing an acrylic resin, a positive electrode, a first separator layer, and a second separator layer. The first separator layer is interposed between the negative electrode and the positive electrode. The second separator layer is interposed between the negative electrode and the first separator layer. The porosity of the second separator layer is higher than that of the first separator layer.

Description

[Technical Field]

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

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

[0003] From the viewpoint of improving fuel efficiency, non-aqueous electrolyte secondary batteries that can be charged with a large current and have high charge acceptance are required as energy sources for the above-mentioned automobiles, etc. For example, Patent Document 1 proposes a technology for improving the charge acceptance of lithium-ion secondary batteries by combining a non-aqueous electrolyte solution containing a specific compound with a negative electrode active material containing a specific lithium-absorbing alloy and element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-188871 Summary of the Invention [Problem to be solved by the invention]

[0005] A nonaqueous electrolyte storage element using an acrylic resin as a binder in a negative electrode active material layer containing a negative electrode active material has higher charge acceptance performance than a nonaqueous electrolyte storage element using a styrene-butadiene rubber as a binder, but a nonaqueous electrolyte storage element using an acrylic resin as a binder in a negative electrode active material layer tends to have an increased resistance after charge-discharge cycles.

[0006] The present invention has been made in light of the above circumstances, and has an object to provide a nonaqueous electrolyte energy storage element that can suppress an increase in resistance after charge-discharge cycling, even when an acrylic resin is used as the binder in the negative electrode active material layer. [Means for solving the problem]

[0007] A nonaqueous electrolyte storage element according to one aspect of the present invention comprises a negative electrode having a negative electrode active material layer containing an acrylic resin, a positive electrode, a first separator layer, and a second separator layer, wherein the first separator layer is interposed between the negative electrode and the positive electrode, and the second separator layer is interposed between the negative electrode and the first separator layer, and the second separator layer has a higher porosity than the first separator layer. [Effects of the Invention]

[0008] In the nonaqueous electrolyte storage element according to one aspect of the present invention, an increase in resistance after charge-discharge cycles can be suppressed even when an acrylic resin is used as the binder in the negative electrode active material layer. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an external perspective view showing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram showing an electricity storage device formed by assembling a plurality of nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] A nonaqueous electrolyte storage element according to one aspect of the present invention comprises a negative electrode having a negative electrode active material layer containing an acrylic resin, a positive electrode, a first separator layer, and a second separator layer, wherein the first separator layer is interposed between the negative electrode and the positive electrode, and the second separator layer is interposed between the negative electrode and the first separator layer, and the second separator layer has a higher porosity than the first separator layer.

[0011] As described above, nonaqueous electrolyte storage elements using an acrylic resin as the binder in the negative electrode active material layer have superior charge acceptance compared to nonaqueous electrolyte storage elements using styrene-butadiene rubber as the binder, but tend to exhibit increased resistance after charge-discharge cycles. However, this nonaqueous electrolyte storage element can suppress the increase in resistance after charge-discharge cycles by including a first separator layer interposed between the negative electrode and the positive electrode and a second separator layer interposed between the negative electrode and the first separator layer, the second separator layer having a higher porosity than the first separator layer. The reason for this is unclear, but is thought to be as follows: When an acrylic resin is used as the binder in the negative electrode active material layer, the acrylic resin has a high swelling rate in nonaqueous electrolytes, so the binder swells with the nonaqueous electrolyte as charge-discharge cycles progress, and the negative electrode active material layer is likely to expand. Therefore, when a low-porosity separator is placed opposite a negative electrode active material layer using an acrylic resin binder, the negative electrode active material layer expands and invades the pores of the separator, causing clogging of the separator pores and resulting in a significant increase in the resistance of the nonaqueous electrolyte storage element. In this nonaqueous electrolyte storage element, by placing a high-porosity second separator layer opposite a negative electrode active material layer using an acrylic resin binder, the negative electrode active material layer is prevented from invading the pores of the low-porosity first separator layer, making clogging of the first separator layer less likely to occur. As a result, the nonaqueous electrolyte storage element is thought to be more effective in suppressing resistance increases after charge-discharge cycles. Therefore, this nonaqueous electrolyte storage element can suppress resistance increases after charge-discharge cycles while taking advantage of the properties of the acrylic resin, which has high charge acceptance. Note that "porosity" is a volume-based value calculated from the mass per unit area, thickness, and true density of the constituent materials.

[0012] It is preferable that the first separator layer be primarily composed of a synthetic resin and the second separator layer be composed of inorganic particles. By using the first separator layer primarily composed of a synthetic resin and the second separator layer be composed of inorganic particles, the effect of suppressing the intrusion of the negative electrode active material layer into the pores of the first separator layer can be enhanced, thereby further improving the effect of suppressing an increase in resistance after charge-discharge cycling of the nonaqueous electrolyte storage element. Here, "primary component" refers to the component with the largest content.

[0013] It is preferable that the second separator layer is further interposed between the positive electrode and the first separator layer. More specifically, it is preferable that at least one second separator layer is interposed between one surface of the negative electrode and the first separator layer, and at least one other second separator layer is interposed between the other surface of the positive electrode and the first separator layer. By providing the second separator layer containing inorganic particles on the side facing the positive electrode, oxidation of the synthetic resin due to direct contact of the first separator layer, which is mainly composed of a synthetic resin, with the positive electrode can be suppressed, and the first separator layer can be protected.

[0014] The porosity of the second separator layer is preferably 45% by volume or more and 85% by volume or less. By setting the porosity of the second separator layer to 45% by volume or more and 85% by volume or less, clogging of the pores in the second separator layer can be suppressed, and the negative electrode active material layer can be suppressed from penetrating into the pores of the first separator layer.

[0015] A nonaqueous electrolyte electricity storage element according to one embodiment of the present invention will be described in detail below.

[0016] <Non-aqueous electrolyte energy storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention includes a negative electrode, a positive electrode, and a nonaqueous electrolyte. A nonaqueous electrolyte secondary battery will be described below as an example of a nonaqueous electrolyte storage element. The positive electrode and negative electrode are alternately stacked or wound with a first separator layer and a second separator layer interposed therebetween to form an electrode assembly. This electrode assembly is housed in a case, and the case is filled with a nonaqueous electrolyte. The nonaqueous electrolyte is interposed between the positive electrode and the negative electrode. The case may be a known metal case, resin case, or the like, commonly used for nonaqueous electrolyte secondary battery cases.

[0017] [Negative electrode] The negative electrode includes a negative electrode substrate and a negative electrode active material layer. The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer is laminated along at least one surface of the negative electrode substrate directly or via an intermediate layer.

[0018] (negative electrode substrate) The negative electrode substrate is a substrate having electrical conductivity. Metals such as copper, nickel, stainless steel, and nickel-plated steel, or alloys thereof, are used as the material for the negative electrode substrate, with copper or a copper alloy being preferred. The negative electrode substrate may be in the form of foil, vapor-deposited film, mesh, porous material, or the like, with foil being preferred from the standpoint 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. Whether or not the negative electrode substrate has "electrical conductivity" is determined by whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 1×10 7 The threshold value is Ω·cm.

[0019] (Negative electrode active material layer) The negative electrode active material layer contains a negative electrode active material and an acrylic resin as a binder.

[0020] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for lithium ion secondary batteries. Examples of the negative electrode active material include metallic Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 , LiTiO 2、 Examples of the carbon material include titanium-containing oxides such as TiNbO; polyphosphate compounds; silicon carbide; and non-graphitic carbons such as graphite, hard carbon, and soft 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.

[0021] "Graphite" refers to graphite that has an average lattice spacing (d 002 ) is a carbon material with a particle size of 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. "Non-graphitic carbon" refers to the carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Non-graphitizable carbon includes non-graphitizable carbon and graphitizable carbon. Non-graphitizable carbon includes, for example, resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, alcohol-derived materials, etc. "Non-graphitizable carbon" refers to a carbon material having the above d 002 The term "easily graphitizable carbon" refers to a carbon material having a particle size of 0.36 nm or more and 0.42 nm or less. 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0022] Here, the "discharged state" refers to a state in which the negative electrode active material, a carbonaceous material, is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released. For example, this refers to a state in which the open circuit voltage of a half cell using a negative electrode containing a carbonaceous material as a negative electrode active material as a working electrode and metallic Li as a counter electrode is 0.7 V or higher.

[0023] The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but the lower limit is preferably 50 mass %, more preferably 80 mass %, and even more preferably 90 mass %, while the upper limit is preferably 99 mass %, more preferably 98 mass %.

[0024] 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.

[0025] 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 and handling of the negative electrode active material becomes easy. By setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit, the electronic conductivity of the active material layer is improved. A pulverizer, a classifier, or the like is used to obtain powder with a predetermined particle size. 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.

[0026] The negative electrode active material layer contains an acrylic resin as a binder. Examples of the "acrylic resin" include a polymer of an acrylic acid ester or a methacrylic acid ester, a copolymer containing polyacrylamide, an acrylic acid ester, or a methacrylic acid ester.

[0027] The content of the acrylic resin in the binder is preferably 99% by mass or more, and may be 100% by mass.

[0028] The lower limit of the binder content in the negative electrode active material layer is preferably 0.2 mass%, more preferably 0.3 mass%, 0.4 mass%, or 0.5 mass%, from the viewpoint of ensuring adhesion, and may be further preferably 0.8 mass%, even more preferably 0.9 mass%, or particularly preferably 1.0 mass%, while the upper limit of this content is preferably 10 mass%, more preferably 5 mass%, more preferably 3 mass%, 2 mass%, or 1 mass%, and particularly preferably 0.8 mass%, from the viewpoint of improving output performance.

[0029] The negative electrode active material layer may contain optional components such as a conductive agent, a thickener, and a filler, as required.

[0030] The conductive agent is not particularly limited as long as it is a material that is conductive. Carbon materials such as graphite, graphitizable carbon, and non-graphitizable carbon also have conductivity, but are not included in the conductive agent in the negative electrode active material layer. Examples of conductive agents other than the carbon materials include other carbonaceous materials, metals, and conductive ceramics. Examples of other carbonaceous materials include other non-graphitic carbons and graphene-based carbons. Examples of other non-graphitic carbons 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 carbons include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent may be in the form of powder or fiber. As the conductive agent, one of these materials may be used alone, or two or more may be mixed and used. Furthermore, these materials may be used in combination. For example, a composite of carbon black and CNTs may be used. Of these, carbon black is preferred from the viewpoint of electron conductivity and coatability, and acetylene black is particularly preferred.

[0031] Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. In addition, when the thickener has a functional group that reacts with lithium, it is preferable to deactivate this functional group in advance by methylation or the like.

[0032] The filler is not particularly limited, and examples of the main component of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, and glass.

[0033] The lower limit of the average thickness of one surface of the negative electrode active material layer is not particularly limited, but may be 30 μm, preferably 40 μm, 44 μm, 49 μm, or 50 μm, more preferably 55 μm, 59 μm, 60 μm, or 62 μm, and even more preferably 64 μm. By having the average thickness of one surface of the negative electrode active material layer at or above the above lower limit, the energy density of the nonaqueous electrolyte storage element can be increased. The upper limit of the average thickness of one surface of the negative electrode active material layer is not particularly limited, but may be 90 μm, preferably 80 μm, 79 μm, or 77 μm, and more preferably 75 μm, 74 μm, or 72 μm. By having the average thickness of one surface of the negative electrode active material layer at or below the above upper limit, the output performance of the nonaqueous electrolyte storage element can be improved, and penetration of the negative electrode active material layer into the pores of the first separator layer can be suppressed, thereby reliably suppressing clogging of the first separator layer. When the nonaqueous electrolyte storage element is used as a power source for automobiles such as electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs), and as a power source for auxiliary equipment, uninterruptible power supplies (UPSs), etc., the average thickness of one surface of the negative electrode active material layer is preferably 50 μm or more and 90 μm or less, and more preferably 62 μm or more and 77 μm or less, from the viewpoint of increasing the energy density. When the nonaqueous electrolyte storage element is used as a power source for automobiles such as hybrid electric vehicles (HEVs), the average thickness of one surface of the negative electrode active material layer is preferably 30 μm or more and 50 μm or less, and more preferably 32 μm or more and 48 μm or more, from the viewpoint of increasing the output performance.

[0034] (middle class) The intermediate layer is a coating layer on the surface of the negative electrode substrate, and 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 configuration of the intermediate layer is not particularly limited, and it can be formed, for example, from a composition containing a binder and a conductive agent.

[0035] [Positive electrode] The positive electrode has a positive electrode substrate and a positive electrode active material layer. The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer is laminated along at least one surface of the positive 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 negative electrode.

[0036] (Positive electrode substrate) The positive electrode substrate is a conductive substrate. Examples of the material for the positive electrode substrate include metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof. Among these, aluminum and aluminum alloys are preferred in terms of the balance between high potential resistance, high conductivity, and cost. Examples of the form of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred in terms 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-H4000 (2014) or JIS-H4160 (2006).

[0037] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the secondary battery.

[0038] (Cathode active material layer) The positive electrode active material layer contains a positive electrode active material. The positive electrode active material can be appropriately selected from, for example, 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 lithium transition metal composite oxides having an α-NaFeO2 type crystal structure, lithium transition metal composite oxides having a spinel type crystal structure, polyanion compounds, chalcogen compounds, sulfur, etc. Examples of the lithium transition metal composite oxides having an α-NaFeO2 type crystal structure include Li[Lix 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) ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1). Lithium transition metal composite oxides with spinel crystal structure include Li x Mn2O4,Li x Ni γ Mn (2-γ) O4, etc. Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, and Li2CoPO4F. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Atoms or polyanions in these materials may be partially substituted with atoms or anion species of other elements. Among these, the lithium transition metal composite oxides are preferred as the positive electrode active material from the viewpoint of achieving high energy density, and nickel-cobalt-manganese-containing lithium transition metal composite oxides containing nickel, cobalt, and manganese as constituent elements in addition to Li are more preferred.

[0039] The surface of the materials listed above as the positive electrode active material may be coated with another material. 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.

[0040] The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but the lower limit is preferably 50 mass %, more preferably 80 mass %, and even more preferably 90 mass %, while the upper limit is preferably 99 mass %, more preferably 98 mass %.

[0041] The positive electrode active material layer may contain 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 may be selected from the materials exemplified for the negative electrode. Note that in the positive electrode active material layer, carbon materials such as graphite, graphitizable carbon, and non-graphitizable carbon are also included as conductive agents.

[0042] The binder for the positive electrode active material layer is not particularly limited, and examples thereof include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0043] [Separator] The nonaqueous electrolyte storage element includes a first separator layer and a second separator layer. The first separator layer is interposed between the negative electrode and the positive electrode, and the second separator layer is interposed between the negative electrode and the first separator layer. A nonaqueous electrolyte is impregnated into the first separator layer and the second separator layer. The first separator layer and the second separator layer separate the positive electrode and the negative electrode and retain the nonaqueous electrolyte between the positive electrode and the negative electrode.

[0044] The porosity of the second separator layer is higher than the porosity of the first separator layer. In the nonaqueous electrolyte storage element, the second separator layer having a higher porosity than the first separator layer is disposed opposite the negative electrode active material layer using an acrylic resin as a binder, thereby improving the effect of suppressing an increase in resistance after charge-discharge cycles.

[0045] The lower limit of the porosity of the first separator layer is preferably 30%, more preferably 31%, 32%, 33%, 34%, or 35%, and in some cases 36%, 37%, 38%, 39%, or 40% is preferred. By setting the porosity of the first separator layer at or above the lower limit, the permeability of the non-aqueous electrolyte can be improved. On the other hand, the upper limit of the porosity of the first separator layer is preferably 50%, more preferably 49%, 48%, 47%, 46%, or 45%, and even more preferably 44%, 43%, 42%, 41%, or 40%. By setting the porosity of the first separator layer at or below the upper limit, the strength of the first separator layer can be improved.

[0046] The lower limit of the porosity of the second separator layer is preferably 45%, and more preferably 46%, 47%, 48%, 49%, or 50%. By setting the porosity of the second separator layer at or above this lower limit, the permeability of the non-aqueous electrolyte can be improved. On the other hand, the upper limit of the porosity of the second separator layer may be 90%, and is preferably 88%, 87%, 86%, or 85%, and more preferably 84%, 83%, 82%, 81%, or 80%. By setting the porosity of the second separator layer at or below this upper limit, the strength of the second separator layer can be improved.

[0047] The difference between the porosity of the first separator layer and the porosity of the second separator layer is preferably 5% to 55%, more preferably 8% to 49%, even more preferably 9% to 48%, and particularly preferably 10% to 45%. By setting the porosity difference within this range, the negative electrode active material layer is prevented from penetrating into the pores of the first separator layer, which further prevents the first separator layer from clogging and achieves a good balance between separator strength and permeability.

[0048] The porosity of the first separator layer and the second separator layer is calculated by the following formula: where W is the mass per unit area [g / cm 3 ] of the first separator layer and the second separator layer. 2 ], and ρ is the true density [g / cm 3 ] of the material constituting the first separator layer or the second separator layer. 3], and t is the thickness [cm] of the first separator layer or the second separator layer. Porosity (%)=100-(W / (ρ×t))×100

[0049] The first separator layer is preferably composed primarily of a synthetic resin. The first separator layer having a synthetic resin as its main component has excellent strength. Examples of synthetic resins that form the main component of the first separator layer include, but are not limited to, polyolefins, polyesters, polyimides, and polyamides (e.g., aromatic polyamides and aliphatic polyamides). Polyolefins also include copolymers of olefins with other monomers. Examples of polyolefins include polyethylene (PE), polypropylene (PP), ethylene-propylene copolymers, ethylene-vinyl acetate copolymers, ethylene-methyl acrylate copolymers, ethylene-ethyl acrylate copolymers, polyolefin derivatives such as chlorinated polyethylene, and ethylene-propylene copolymers.

[0050] Among these resins, polyolefin, polyester and aliphatic polyamide are preferred, polyolefin is more preferred, and PE and PP are even more preferred, as PE and PP can exhibit good shutdown function.

[0051] The first separator layer may be formed of, for example, a woven fabric, a nonwoven fabric, or a microporous membrane. Among these, nonwoven fabrics and microporous membranes are preferred, and microporous membranes are more preferred. Microporous membranes have advantages such as high strength. Nonwoven fabrics have advantages such as high liquid retention.

[0052] The second separator layer preferably contains inorganic particles. The inclusion of inorganic particles in the second separator layer can enhance the effect of suppressing the intrusion of the negative electrode active material layer into the pores of the first separator layer, thereby further improving the effect of suppressing an increase in resistance after charge-discharge cycling of the nonaqueous electrolyte storage element. The second separator layer is a porous layer. The second separator layer is typically composed of inorganic particles and a binder, and may contain other components.

[0053] Examples of inorganic particles contained in the second separator layer include particles of oxides such as alumina, silica, zirconia, titania, magnesia, ceria, yttria, zinc oxide, and iron oxide, nitrides such as silicon nitride, titanium nitride, and boron nitride, silicon carbide, calcium carbonate, aluminum sulfate, barium sulfate, aluminum hydroxide, potassium titanate, barium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, and magnesium silicate. Among these, particles of alumina, silica, titania, or barium sulfate are preferred.

[0054] Specific types of binders for the second separator layer include those exemplified as binders for the positive electrode active material layer described above.

[0055] The second separator layer may be formed integrally with the first separator layer or may be independent of the first separator layer, and may be provided so as to cover the negative electrode active material layer.

[0056] Preferably, the second separator layer is further interposed between the positive electrode and the first separator layer. More specifically, preferably, at least one second separator layer is interposed between one surface of the negative electrode and the first separator layer, and at least one other second separator layer is interposed between the other surface of the positive electrode and the first separator layer. By providing the second separator layer containing inorganic particles on the side facing the positive electrode, oxidation of the synthetic resin due to direct contact of the first separator layer, mainly composed of a synthetic resin, with the positive electrode can be suppressed, thereby protecting the first separator layer.

[0057] The lower limit of the average thickness of the first separator layer is preferably 4 μm, more preferably 8 μm. The upper limit of this average thickness is preferably 30 μm, more preferably 20 μm. By setting the average thickness of the first separator layer to be equal to or greater than the lower limit, short-circuiting between the positive electrode and the negative electrode can be prevented with high reliability. Furthermore, by setting the average thickness of the first separator layer to be equal to or less than the upper limit, the energy density of the nonaqueous electrolyte storage element can be increased.

[0058] The lower limit of the average thickness of the second separator layer is preferably 1 μm, more preferably 2 μm. Meanwhile, the upper limit of the average thickness of the second separator layer is preferably 10 μm, more preferably 6 μm. By setting the average thickness of the second separator layer to be equal to or greater than the lower limit, the negative electrode active material layer is prevented from penetrating into the pores of the first separator layer, thereby reliably preventing clogging of the first separator layer. By setting the average thickness of the second separator layer to be equal to or less than the upper limit, the energy density of the nonaqueous electrolyte storage element can be increased. When two or more second separator layers are provided, the average thickness of the second separator layer is the average of the average thicknesses of the respective second separator layers.

[0059] The ratio of the average thickness of the second separator layer to the average thickness of the first separator layer is preferably less than 0.5, preferably 0.4 or less, and more preferably 0.3 or less. By setting the ratio of the average thickness of the second separator layer to the average thickness of the first separator layer within the above range, the energy density of the nonaqueous electrolyte storage element can be increased. The lower limit of the ratio of the average thickness of the second separator layer to the average thickness of the first separator layer is preferably 0.1 or more, more preferably 0.2 or more. By setting the ratio of the average thickness of the second separator layer to the average thickness of the first separator layer to be equal to or greater than the above lower limit, the negative electrode active material layer is prevented from penetrating into the pores of the first separator layer, and clogging of the first separator layer can be reliably prevented.

[0060] The lower limit of the ratio of the sum of the average thickness of the first separator layer and the second separator layer to the average thickness of the negative electrode active material layer is, for example, 0.05, or may be 0.10, preferably 0.15, more preferably 0.20, and in some cases, 0.25, 0.30, or 0.38. The upper limit of the ratio of the sum of the average thickness of the first separator layer and the second separator layer to the average thickness of the negative electrode active material layer is, for example, 1.30, preferably 1.00, more preferably 0.80, 0.75, or 0.65, and in some cases, 0.60, 0.50, or 0.45. By setting the ratio of the sum of the average thickness of the first separator layer and the second separator layer to the average thickness of the negative electrode active material layer within the above range, the energy density of the nonaqueous electrolyte storage element can be increased, and penetration of the negative electrode active material layer into the pores of the first separator layer can be suppressed, thereby more reliably suppressing clogging of the first separator layer.

[0061] The lower limit of the ratio of the average thickness of the first separator layer to the average thickness of the negative electrode active material layer is, for example, 0.04, preferably 0.08, and more preferably 0.11. The upper limit of the ratio of the average thickness of the first separator layer to the average thickness of the negative electrode active material layer is, for example, 1.00, and may be 0.80, 0.70, 0.65, 0.50, or 0.45, with 0.40 or 0.30 being preferred. By setting the ratio of the average thickness of the first separator layer to the average thickness of the negative electrode active material layer within the above range, the energy density of the nonaqueous electrolyte storage element can be increased, and the separator's effect of suppressing an increase in reaction force due to expansion of the negative electrode active material layer can be enhanced.

[0062] The lower limit of the ratio of the average thickness of the second separator layer to the average thickness of the negative electrode active material layer is, for example, 0.01, preferably 0.02, and more preferably 0.04, 0.06, or 0.08. The upper limit of the ratio of the average thickness of the second separator layer to the average thickness of the negative electrode active material layer is, for example, 0.33, preferably 0.20, 0.17, or 0.13, and may be 0.10 or 0.08. By setting the ratio of the average thickness of the second separator layer to the average thickness of the negative electrode active material layer within the above range, the energy density of the nonaqueous electrolyte storage element can be increased, and penetration of the negative electrode active material layer into the pores of the first separator layer can be suppressed, thereby more reliably suppressing clogging of the first separator layer.

[0063] When the first separator layer is mainly composed of a synthetic resin and the positive electrode active material layer and the first separator layer are in direct contact with each other, the upper limit charge potential of the positive electrode is set to 4.15 V vs. Li / Li in order to suppress oxidation of the first separator layer. + The following is preferable: 4.10V vs. Li / Li + In order to set the upper limit charging potential of the positive electrode in the above range, the upper limit charging voltage of the nonaqueous electrolyte storage element may be controlled by setting a charger or the like. + The following materials may be used:

[0064] [Non-aqueous electrolyte] The nonaqueous electrolyte can be appropriately selected from known nonaqueous electrolytes. A nonaqueous electrolyte solution is used as the nonaqueous electrolyte. The nonaqueous electrolyte solution contains a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent.

[0065] (non-aqueous solvent) 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 the cyclic carbonate 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, catechol carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate, with EC being preferred among these.

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

[0069] (electrolyte salt) 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] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2, and lithium salts having a halogenated hydrocarbon group 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.

[0071] The content of the electrolyte salt in the non-aqueous electrolyte is 0.1 mol / dm 3 More than 2.5mol / dm 3 It is preferable that the value is 0.3 mol / dm or less. 3 More than 2.0mol / dm 3 It is more preferable that it is 0.5 mol / dm or less. 3 More than 1.7mol / dm 3 It is more preferable that it is 0.7 mol / dm or less. 3 More than 1.5mol / dm 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] (additives) The non-aqueous electrolyte may contain an additive. Examples of the additive include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, 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; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclohexyl benzene. hexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, 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, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, etc. These additives may be used alone or in combination of two or more.

[0073] The content of the additive in the non-aqueous electrolyte solution 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. By setting the content of the additive in the above range, it is possible to improve the capacity retention performance or charge / discharge cycle performance after high-temperature storage of the non-aqueous electrolyte storage element, and to further improve safety.

[0074] The nonaqueous electrolyte may be a combination of a nonaqueous electrolytic solution and a solid electrolyte.

[0075] [Specific Configuration of Nonaqueous Electrolyte Energy Storage Element] The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include cylindrical batteries, pouch film batteries, prismatic batteries, flat batteries, coin batteries, and button batteries.

[0076] FIG. 1 shows a nonaqueous electrolyte storage element 1 as an example of a prismatic battery. Note that this figure is a see-through view of the inside of a case 3. An electrode assembly 2 having a positive electrode and a negative electrode wound with a separator sandwiched between them is housed in the prismatic case 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode current collector 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode current collector 51. A nonaqueous electrolyte is poured into the case 3.

[0077] [Method of manufacturing nonaqueous electrolyte energy storage element] A method for manufacturing a nonaqueous electrolyte storage element according to one embodiment of the present invention includes housing the negative electrode, the positive electrode, and the nonaqueous electrolyte in a case. The negative electrode can be obtained by laminating the negative electrode active material layer directly onto a negative electrode substrate or via an intermediate layer. The lamination of the negative electrode active material layer is performed by applying a negative electrode mixture paste containing a negative electrode active material and an acrylic resin to the negative electrode substrate. Similarly to the negative electrode, the positive electrode can be obtained by laminating the positive electrode active material layer directly onto a positive electrode substrate or via an intermediate layer. The lamination of the positive electrode active material layer is performed by applying a positive electrode mixture paste to the positive electrode substrate. The negative electrode mixture paste and the positive electrode mixture paste may contain a dispersion solvent. Examples of the dispersion solvent include aqueous solvents such as water and mixed solvents mainly containing water; and organic solvents such as N-methylpyrrolidone and toluene.

[0078] The method for manufacturing the nonaqueous electrolyte storage element also includes stacking the negative electrode and the positive electrode with a first separator layer and a second separator layer interposed therebetween, as described above. The first separator layer is interposed between the negative electrode and the positive electrode, and the second separator layer is interposed between the negative electrode and the first separator layer. By stacking the negative electrode and the positive electrode with the first separator layer and the second separator layer interposed therebetween, an electrode assembly is formed.

[0079] The negative electrode, positive electrode, non-aqueous electrolyte, etc. can be housed in a case by a known method. After the housing, the housing opening is sealed to obtain a non-aqueous electrolyte storage element. Details of each element constituting the non-aqueous electrolyte storage element obtained by the above manufacturing method are as described above.

[0080] [Other embodiments] The nonaqueous electrolyte storage element of the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, or part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0081] In the above embodiment, the nonaqueous electrolyte storage element has been mainly described as a nonaqueous electrolyte secondary battery, but other nonaqueous electrolyte storage elements may also be used. Examples of other nonaqueous electrolyte storage elements include capacitors (electric double layer capacitors, lithium ion capacitors), etc. Examples of nonaqueous electrolyte secondary batteries include lithium ion nonaqueous electrolyte secondary batteries.

[0082] Furthermore, although a wound electrode body is used in the above embodiment, a laminated electrode body formed from a laminate of multiple sheet bodies each having a positive electrode, a negative electrode, a first separator layer, and a second separator layer may also be provided.

[0083] The present invention can also be realized as an electricity storage device including a plurality of the above-described nonaqueous electrolyte electricity storage elements. Furthermore, an electricity storage unit can be configured by using one or more nonaqueous electrolyte electricity storage elements of the present invention, and this electricity storage unit can be used to configure an electricity storage device. The electricity storage device can be used as a power source for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). Furthermore, the electricity storage device can be used in various power supply devices such as engine starting power supplies, auxiliary power supplies, and uninterruptible power supplies (UPS).

[0084] 2 shows an example of an electricity storage device 30 in which electricity storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte electricity storage elements 1, are further assembled. The electricity storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte electricity storage elements 1, and a bus bar (not shown) that electrically connects two or more electricity storage units 20. The electricity storage unit 20 or the electricity storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte electricity storage elements. [Example]

[0085] 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.

[0086] [Example 1 and Comparative Example 2] (Negative electrode) A negative electrode mixture paste containing graphite as the negative electrode active material, a binder listed in Table 1, and carboxymethyl cellulose (CMC) as a thickener, with water as the dispersion solvent, was prepared. The mixing ratio of the negative electrode active material, binder, and thickener was 98:1:1 by mass. The negative electrode mixture paste was applied to one side of a 10 μm-thick copper foil as a negative electrode substrate, dried, and pressed to form a negative electrode active material layer with an average thickness of 67 μm, and negative electrodes of the examples and comparative examples were obtained. (non-aqueous electrolyte) LiPF6 was added to a non-aqueous solvent consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 30:35:35. 3 The solution was dissolved to obtain a non-aqueous electrolyte. (positive electrode) NCM (LiNi) with α-NaFeO2 type crystal structure 0.6 Co 0.2 Mn 0.2 A positive electrode containing 02) as the positive electrode active material was fabricated. A positive electrode mixture paste was prepared containing the above positive electrode active material, polyvinylidene fluoride (PVDF) as a binder, and acetylene black as a conductive agent, with N-methyl-2-pyrrolidone (NMP) as a dispersion solvent. The mixing ratio of the positive electrode active material, binder, and conductive agent was 94:3:3 by mass. The positive electrode mixture paste was applied to one side of a positive electrode substrate, dried, and pressed to form a positive electrode active material layer. Aluminum foil with a thickness of 15 μm was used as the positive electrode substrate. (separator) The separator was prepared by laminating a porous layer (average thickness 4 μm, porosity 48%) containing inorganic particles and a binder on one side of a polyolefin microporous substrate (average thickness 20 μm, porosity 37%). Here, the polyolefin microporous substrate corresponds to the first separator layer, and the porous layer corresponds to the second separator layer.

[0087] (porosity of separator) The porosity [%] of the first separator layer and the second separator layer was calculated using the following formula. Porosity (%)=100-(W / (ρ×t))×100 W: Mass per unit area [g cm -2 ] ρ: True density of constituent materials [g cm -3 ] t: thickness [cm] Table 1 shows the porosity of the first separator layer and the second separator layer.

[0088] (Fabrication of non-aqueous electrolyte energy storage element) A nonaqueous electrolyte storage element was assembled using the positive electrode and the negative electrode. The positive electrode, first separator layer, second separator layer, and negative electrode were laminated together so that the positive electrode active material layer and the negative electrode active material layer faced each other with the first separator layer and second separator layer interposed therebetween, the first separator layer was interposed between the negative electrode and the positive electrode, and the second separator layer was interposed between the negative electrode and the first separator layer. The nonaqueous electrolyte was used as the nonaqueous electrolyte.

[0089] [Example 2 and Comparative Example 3] The separator used was a polyolefin microporous substrate (average thickness 14 μm, porosity 45%) with porous layers (average thickness 3 μm, porosity: 58%) containing inorganic particles and a binder laminated on both sides. Here, the polyolefin microporous substrate corresponds to the first separator layer, and the porous layers correspond to the second separator layer. The nonaqueous electrolyte storage elements of Example 2 and Comparative Example 3 were obtained in the same manner as in Example 1 and Comparative Example 2, except that the positive electrode, first separator layer, second separator layer, and negative electrode were laminated so that one second separator layer was interposed between the negative electrode and the first separator layer, and the other second separator layer was interposed between the positive electrode and the first separator layer.

[0090] [Comparative Examples 1 and 4] The separator used was a polyolefin microporous substrate (average thickness 14 μm, porosity 44%) with a porous layer (average thickness 4 μm, porosity: 75%) containing inorganic particles and a binder laminated on one side. Here, the polyolefin microporous substrate corresponds to the first separator layer, and the porous layer corresponds to the second separator layer. The nonaqueous electrolyte storage elements of Comparative Examples 1 and 4 were obtained in the same manner as in Example 1 and Comparative Example 2, except that the positive electrode, first separator layer, second separator layer, and negative electrode were laminated so that the second separator layer was interposed between the positive electrode active material and the first separator layer.

[0091] [evaluation] (Initial performance evaluation) Each of the obtained nonaqueous electrolyte storage elements was subjected to constant current charging at a charging current of 0.2 C up to 4.25 V at a temperature of 25°C, followed by constant voltage charging at 4.25 V. The charging was terminated after 7 hours of charging. After a 10-minute pause, the element was discharged at a constant current of 0.2 C down to 2.75 V, followed by a 10-minute pause. Next, the element was charged at a constant current of 1.0 C up to 4.25 V at a temperature of 25°C, followed by constant voltage charging at 4.25 V. The charging was terminated after 3 hours of charging. After a 10-minute pause, the element was discharged at a constant current of 1.0 C down to 2.75 V. The discharge capacity at this 1.0 C discharge current was designated the "initial discharge capacity." Each of the obtained nonaqueous electrolyte storage elements was subjected to constant current charging at 25°C with a charging current of 1.0 C until the SOC (State of Charge) reached 50%. The elements were charged for 30 seconds at a charging current of 0.2 C, 0.5 C, or 1.0 C at 25°C. After each charge, the elements were discharged at a constant current of 1.0 C until the SOC reached 50%. The relationship between the current and the voltage 10 seconds after the start of charging at each charging current was plotted, and the DC input resistance (initial DC input resistance) was calculated from the slope of the straight line obtained from the plot of the three points.

[0092] (Charge-discharge cycle test) After the initial performance evaluation, each nonaqueous electrolyte storage element was subjected to a charge-discharge cycle test under the following conditions. After storing the element in a 45°C thermostatic chamber for 3 hours, it was charged at a constant current of 1.0C up to a voltage where the SOC (State of Charge) was 100%. A 10-minute rest period was allowed after charging. Subsequently, it was discharged at a constant current of 1.0C down to a voltage where the SOC was 0%, followed by a 10-minute rest period. This charge and discharge process constitutes one cycle, and this cycle was repeated 100 times. The charge, discharge, and rest periods were all performed in a 45°C thermostatic chamber.

[0093] (DC input resistance increase rate after charge / discharge cycle) After the charge-discharge cycle test, the DC input resistance (DC input resistance after charge-discharge cycles) of each nonaqueous electrolyte energy storage element was determined in the same manner as in the "initial performance evaluation" section above. The increase rate (%) of the DC input resistance after charge-discharge cycles relative to the initial DC input resistance was determined. Then, the ratio of the DC input resistance increase rate of Examples 1 and 2 to Comparative Example 1 was calculated, and the ratio of the DC input resistance increase rate of Comparative Examples 2 and 3 to Comparative Example 4 was calculated. The results are shown in Table 1 below.

[0094] [Table 1]

[0095] As shown in Table 1, the DC input resistance increase rate after charge-discharge cycling in Examples 1 and 2, in which the negative electrode active material layer contains an acrylic resin as a binder and the second separator layer is arranged facing the negative electrode, is significantly reduced compared to the DC input resistance increase rate after charge-discharge cycling in Comparative Example 1, in which the negative electrode active material layer contains an acrylic resin as a binder and the second separator layer is arranged facing the negative electrode, the porosity of which is higher than that of the first separator layer. Furthermore, it is clear that the DC input resistance increase rate after charge-discharge cycling in Example 2, in which the second separator layer is arranged facing the negative electrode and the positive electrode, is particularly significantly reduced.

[0096] On the other hand, in Comparative Examples 2 to 3, in which the negative electrode active material layer contains styrene-butadiene rubber as a binder, even though the second separator is disposed opposite the negative electrode, it is clear that the increase rate of DC input resistance after charge-discharge cycles is not sufficiently reduced compared to Comparative Example 4, in which the second separator layer is not disposed opposite the negative electrode.

[0097] As described above, the nonaqueous electrolyte electricity storage element was shown to have an excellent effect of suppressing an increase in resistance after charge-discharge cycles. [Industrial Applicability]

[0098] The present invention is suitably used as a nonaqueous electrolyte storage element, including a nonaqueous electrolyte secondary battery used as a power source for electronic devices such as personal computers and communication terminals, automobiles, and the like. [Explanation of symbols]

[0099] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 Cases 4 Positive terminal 5 Negative terminal 20 Energy storage unit 30 Energy storage device 41 Positive electrode current collector 51 Negative electrode current collector

Claims

1. a negative electrode having a negative electrode active material layer containing an acrylic resin; A positive electrode and a first separator layer; a second separator layer; It is equipped with the first separator layer is interposed between the negative electrode and the positive electrode, the second separator layer is interposed between the negative electrode and the first separator layer; a porous surface layer formed on at least one surface of the substrate, the surface having a plurality of porous convex portions and a plurality of concave portions existing as voids, the surface layer comprising a first layer extending in a thickness direction from the lowest of the plurality of concave portions to the highest of the plurality of convex portions; and a porous second layer formed between the first layer and the substrate, the second layer having a higher porosity than the substrate, the first layer having a higher porosity than the substrate, the first layer having a higher porosity than the substrate, the first layer having a higher porosity than the second layer, and the thickness of the first layer being equal to or greater than the thickness of the second layer.

2. 2. The nonaqueous electrolyte storage element according to claim 1, wherein said first separator layer is mainly composed of a synthetic resin, and said second separator layer contains inorganic particles.

3. 3. The nonaqueous electrolyte storage element according to claim 2, wherein said second separator layer is further interposed between said positive electrode and said first separator layer.

4. 4. The nonaqueous electrolyte storage element according to claim 1, wherein the porosity of the second separator layer is 45% by volume or more and 85% by volume or less.

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