Non-aqueous electrolyte electric power storage element

Abstract

A non-aqueous electrolyte electric power storage element according to one aspect of the present invention comprises a positive electrode, a negative electrode, and a separator that is disposed between the positive electrode and the negative electrode. The negative electrode contains a negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum. The creep deformation in the separator after a load of 2 MPa is retained for 60 seconds at a temperature of 65°C is 0.1 or less, and the air permeability resistance of the separator is 120 seconds / 100 mL to 200 seconds / 100 mL.

Description

Non-aqueous electrolyte energy storage element

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

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. 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 charge-transporting ions between the electrodes. Capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte energy storage elements other than secondary batteries.

[0003] Non-aqueous electrolyte storage elements have been developed that use, as the negative electrode active material, elements such as silicon, tin, and aluminum, or compounds containing these elements (see Patent Documents 1 to 3). These negative electrode active materials have advantages such as a larger discharge capacity than carbon materials such as graphite, which are widely used as negative electrode active materials.

[0004] JP 2015-053152 A JP 2014-120459 A JP 2002-121023 A

[0005] In a non-aqueous electrolyte electricity storage element using a negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum, an increase in resistance is likely to occur with charge-discharge cycles.

[0006] An object of the present invention is to provide a nonaqueous electrolyte electricity storage element that uses a negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum, and that has a low rate of increase in resistance after charge-discharge cycling.

[0007] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode contains a negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum, and the separator has a creep strain of 0.1 or less after holding a load of 2 MPa at a temperature of 65°C for 60 seconds, and an air permeation resistance of 120 sec / 100 mL or more and 200 sec / 100 mL or less.

[0008] According to the present invention, it is possible to provide a nonaqueous electrolyte electricity storage element that uses a negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum, and that has a low rate of increase in resistance after charge-discharge cycling.

[0009] Fig. 1 is a perspective view showing one embodiment of a nonaqueous electrolyte electricity storage element, and Fig. 2 is a schematic view showing one embodiment of an electricity storage device formed by assembling a plurality of nonaqueous electrolyte electricity storage elements.

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

[0011] [1] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode contains a negative electrode active material including at least one element selected from the group consisting of silicon, tin, and aluminum, and the separator has a creep strain of 0.1 or less after holding a load of 2 MPa at a temperature of 65°C for 60 seconds, and an air permeation resistance of the separator of 120 sec / 100 mL or more and 200 sec / 100 mL or less.

[0012] The nonaqueous electrolyte storage element described in [1] above is a nonaqueous electrolyte storage element that uses a negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum, and exhibits a low resistance increase rate after charge / discharge cycling. The reason for this effect is unclear, but the following is speculated. Negative electrode active materials containing at least one element selected from the group consisting of silicon, tin, and aluminum undergo large volume changes during charge / discharge, and the expansion of the negative electrode active material during charging easily compresses the separator. In conventional nonaqueous electrolyte storage elements that use such negative electrode active materials, the separator is significantly compressed with repeated charge / discharge cycles, causing clogging of the separator. This reduces the ionic conductivity of the nonaqueous electrolyte contained in the separator voids, resulting in an increase in resistance. In contrast, the nonaqueous electrolyte storage element described in [1] above uses a separator that has a creep strain of 0.1 or less after holding a load of 2 MPa at 65°C for 60 seconds and an air permeability resistance of 120 sec / 100 mL or more and 200 sec / 100 mL or less. Separators with small creep strain are less likely to be compressed. Furthermore, separators with an air permeability resistance of 120 sec / 100 mL or more and 200 sec / 100 mL or less exhibit sufficient ionic conductivity for the nonaqueous electrolyte contained in the voids. The nonaqueous electrolyte storage element described in [1] above is presumed to have a low rate of resistance increase after charge / discharge cycling, despite the use of a negative electrode active material that experiences a large volume change during charge / discharge.

[0013] The "creep strain of a separator after a load of 2 MPa is applied for 60 seconds at 65°C" refers to the creep strain when a load is applied in the thickness direction of the separator, and is specifically a value measured by the following method. First, the thickness (A) of a sample in an unloaded state at 65°C, which is a stack of 200 dry separators, is measured. Next, a load cell creep tester (manufactured by Mize Testing Instruments Co., Ltd.) is used to compress the sample at 65°C by pressing a 50 mm diameter cylindrical indenter against the sample in the thickness direction. After the compressive stress reaches 2 MPa, the sample is maintained in this state for 60 seconds. The thickness (B) of the sample after maintaining the stressed state for 60 seconds is measured while maintaining the state. The creep strain is calculated from the unloaded sample thickness (A) and the sample thickness (B) after maintaining a load of 2 MPa for 60 seconds at 65°C using the following formula (1): Creep strain = (A - B) / A (1)

[0014] The "air resistance" is a value measured by the "Gurley tester method" in accordance with JIS-P-8117 (2009), and is the average value of measurements taken at 10 different positions.

[0015] [2] In the nonaqueous electrolyte storage element according to [1] above, the separator may have a base material layer made of a resin, and the air resistance of the separator relative to the average thickness of the base material layer may be 15 seconds / (100 mL μm) or less.

[0016] A low air permeation resistance of the separator relative to the average thickness of the separator substrate layer means that the pores of the separator are relatively large and are less likely to become clogged even when compressed. Therefore, the nonaqueous electrolyte storage element described in [2] above, which includes such a separator, has a lower rate of increase in resistance after charge-discharge cycling.

[0017] The average thickness of the substrate layer of the separator is the average value of thicknesses measured at any five points on the substrate layer.

[0018] [3] In the nonaqueous electrolyte storage element according to the above [1] or [2], the separator may have an air resistance of 140 seconds / 100 mL or more and 200 seconds / 100 mL or less.

[0019] The nonaqueous electrolyte storage element described in the above [3] has a lower resistance increase rate after charge-discharge cycling.

[0020] [4] In the nonaqueous electrolyte storage element according to the above [1], the separator may have a base material layer made of a resin, and the base material layer may have an average thickness of 14 μm or more.

[0021] The nonaqueous electrolyte storage element described in [4] above has a lower resistance increase rate after charge-discharge cycling.

[0022] [5] In the nonaqueous electrolyte storage element according to any one of [1] to [4] above, the negative electrode may have a negative electrode active material layer containing the negative electrode active material, the negative electrode active material may be silicon oxide, and the content of the silicon oxide in the negative electrode active material layer may be 2% by mass or more and 20% by mass or less.

[0023] The nonaqueous electrolyte storage element described in the above [5] has a lower resistance increase rate after charge-discharge cycles due to the appropriate expansion of the negative electrode active material layer and other factors.

[0024] Hereinafter, a nonaqueous electrolyte electricity storage element, an electricity storage device, a method for manufacturing a nonaqueous electrolyte electricity storage element according to one 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.

[0025] <Non-aqueous electrolyte storage element> A non-aqueous electrolyte storage element (hereinafter also simply referred to as "storage element") according to one embodiment of the present invention comprises an electrode assembly having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container that accommodates the electrode assembly and the non-aqueous electrolyte. The electrode assembly is typically a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with separators interposed therebetween, or a wound type in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween and wound. The non-aqueous electrolyte exists in a state in which it is impregnated into the positive electrode, the negative electrode, and the separator. As an example of a non-aqueous electrolyte storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

[0026] (Positive Electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0027] 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 －２ 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).

[0028] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density per volume of the nonaqueous electrolyte storage element.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] In one embodiment of the present invention, the positive electrode active material is preferably a lithium transition metal composite oxide, such as α-NaFeO ２ The positive electrode active material preferably contains at least one element selected from the group consisting of nickel, manganese, and cobalt, and more preferably contains nickel, manganese, and cobalt.

[0033] 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).

[0034] 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.

[0035] The content of the positive electrode active material in the positive electrode active material layer is preferably 70% by mass to 99% by mass, more preferably 80% by mass to 98% by mass, and even more preferably 90% 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.

[0036] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbon materials, metals, conductive ceramics, etc. Examples of carbon materials include graphite, non-graphitic carbon, graphene-based carbon, etc. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, carbon black, etc. Examples of carbon black include furnace black, acetylene black, ketjen black, etc. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerene, etc. The conductive agent may be in the form of powder, fiber, etc. As the conductive agent, one of these materials may be used alone, or two or more may be mixed and used. These materials may also be used in combination. For example, a composite material 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.

[0037] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the content of the conductive agent in this range, the energy density of the nonaqueous electrolyte storage element can be increased.

[0038] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, polyacrylates, polymethacrylates, and polyimides; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0039] The content of the binder in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 2% by mass to 5% by mass, by which the positive electrode active material can be stably maintained.

[0040] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like.

[0041] The content of the thickener in the positive electrode active material layer may be, for example, 0.1% by mass to 6% by mass, or 0.5% by mass to 3% by mass, or 1% by mass or less, or the positive electrode active material layer may not contain a thickener.

[0042] The filler is not particularly limited, and examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof.

[0043] The content of the filler in the positive electrode active material layer may be, for example, 0.1% by mass to 8% by mass, or 0.5% by mass to 5% by mass, 3% by mass or less, or 1% by mass or less, or the positive electrode active material layer may not contain a filler.

[0044] 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.

[0045] The mass per unit area of ​​the positive electrode active material layer is 10 mg / cm ２ 30mg / cm or more ２ Preferably, 15 mg / cm or less ２ 20mg / cm or more ２ The following is more preferable. The mass per unit area of ​​the positive electrode active material layer refers to the mass per unit area of ​​one positive electrode active material layer. For example, when positive electrode active material layers are provided on both sides of a positive electrode substrate, this refers to the mass per unit area of ​​the positive electrode active material layer on one side. The same applies to the mass per unit area of ​​the negative electrode active material layer described below.

[0046] 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.

[0047] 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.

[0048] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while increasing the energy density per volume of the nonaqueous electrolyte storage element.

[0049] 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.

[0050] The negative electrode active material used is a negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum. Examples of such negative electrode active materials include simple substances of these elements and compounds containing these elements (oxides, nitrides, carbides, alloys, etc.). Examples of negative electrode active materials containing silicon include simple silicon, silicon oxide, silicon nitride, silicon carbide, etc. Examples of compounds containing tin include simple tin, tin oxide, tin nitride, tin alloys (Sn ６ Cu ５ Examples of negative electrode active materials containing aluminum include aluminum alone, aluminum oxide, aluminum nitride, aluminum carbide, and aluminum alloys. Among these, a single element or an oxide of at least one element selected from the group consisting of silicon, tin, and aluminum is preferred. Silicon alone or a compound containing silicon is also preferred, with silicon oxide being more preferred. Pre-doped negative electrode active materials containing at least one element selected from the group consisting of silicon, tin, and aluminum can also be used. That is, these negative electrode active materials may further contain an element (e.g., lithium) that constitutes charge transport ions. The negative electrode active materials can be used alone or in combination of two or more.

[0051] The shape of the negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum is not particularly limited, but particulate form is preferred. The average particle size of the negative electrode active material can be, for example, 1 nm to 100 μm, or may be 10 nm to 1 μm. 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. A pulverizer, a classifier, or the like is used to obtain particles with a predetermined particle size. The pulverization method and classification method can be selected, for example, from the methods exemplified for the positive electrode above.

[0052] The negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum preferably has a surface coated with a conductive material such as a carbon material. By using such a negative electrode active material, the electronic conductivity of the negative electrode active material layer can be improved. When the negative electrode active material is in the form of particles coated with a conductive material, the mass ratio of the conductive material to the total amount of the negative electrode active material and the conductive material coating it is, for example, preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less.

[0053] The lower limit of the content of the negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum relative to the total negative electrode active material may be, for example, 1% by mass, but is preferably 2% by mass, more preferably 3% by mass, and even more preferably 4% by mass. By setting the content of the negative electrode active material relative to the total negative electrode active material at or above the above lower limit, it is possible to increase the discharge capacity of the nonaqueous electrolyte storage element. On the other hand, the upper limit of the content of the negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum relative to the total negative electrode active material may be, for example, 100% by mass, but is preferably 90% by mass, more preferably 80% by mass, even more preferably 60% by mass, and in some cases even more preferably 40% by mass, 20% by mass, or 10% by mass. By setting the content of the negative electrode active material relative to the total negative electrode active material at or below the above upper limit, it is possible to further reduce the resistance increase rate after charge / discharge cycling. The content of the negative electrode active material relative to the total amount of the negative electrode active material can be set within a range that is a combination of any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0054] The lower limit of the content of the negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum in the negative electrode active material layer may be, for example, 1% by mass, but is preferably 2% by mass, more preferably 3% by mass, and even more preferably 4% by mass. By setting the content of the negative electrode active material in the negative electrode active material layer to be equal to or greater than the above lower limit, it is possible to increase the discharge capacity of the nonaqueous electrolyte storage element. On the other hand, the upper limit of the content of the negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum in the negative electrode active material layer may be, for example, 100% by mass, but is preferably 90% by mass, more preferably 80% by mass, even more preferably 60% by mass, and in some cases even more preferably 40% by mass, 20% by mass, or 10% by mass. By setting the content of the negative electrode active material in the negative electrode active material layer to be equal to or less than the above upper limit, it is possible to further reduce the resistance increase rate after charge / discharge cycling. The content of the negative electrode active material in the negative electrode active material layer can be set within a range that is a combination of any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0055] In one embodiment of the present invention, it is preferable to use a carbon material together with a negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum.

[0056] Examples of the carbon material include graphite and non-graphitic carbon, with graphite being preferred. By including such a carbon material as the negative electrode active material, it is possible to further reduce the rate of increase in resistance after charge-discharge cycling.

[0057] "Graphite" refers to a graphite material that has an average lattice spacing (d ００２ ) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Natural graphite and artificial graphite may be used alone or in combination.

[0058] "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.

[0059] Here, the "discharged state" of the carbon material refers to a state in which the carbon material, which is the negative electrode active material, is discharged so that lithium ions that can be absorbed and released during charging and discharging are sufficiently released from the carbon material. For example, this refers to a state in which the open circuit voltage is 0.7 V or higher in a half cell 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.

[0060] The lower limit of the carbon material content relative to the total negative electrode active material may be, for example, 0% by mass, but is preferably 10% by mass, more preferably 20% by mass, even more preferably 40% by mass, and even more preferably 60% by mass, 80% by mass, or 90% by mass. By setting the carbon material content at or above the above lower limit, it is possible to further reduce the resistance increase rate after charge / discharge cycling. The upper limit of the carbon material content relative to the total negative electrode active material is preferably 99% by mass, more preferably 98% by mass, even more preferably 97% by mass, and even more preferably 96% by mass. By setting the carbon material content at or below the above upper limit, it is possible to increase the content of the negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum, thereby increasing the discharge capacity of the nonaqueous electrolyte storage element. The carbon material content relative to the total negative electrode active material can be within a range that combines any of the above lower limits and any of the above upper limits.

[0061] The negative electrode active material may further include a negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum, and a negative electrode active material other than the carbon material. Examples of other negative electrode active materials include known negative electrode active materials commonly used in lithium-ion secondary batteries, etc. However, the lower limit of the total content of the negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum and the carbon material relative to the total negative electrode active material is preferably 90 mass%, more preferably 99 mass%. Meanwhile, the upper limit of this total content may be 100 mass%. Thus, the effects of the present invention can be more fully achieved by using only a negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum, or by using only a negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum and the carbon material as the negative electrode active material.

[0062] The content of the negative electrode active material in the negative electrode active material layer may be, for example, 100% by mass, but is preferably 70% by mass to 99% by mass, more preferably 90% by mass to 98% by mass, and even more preferably 92% by mass to 97% by mass. 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.

[0063] As the conductive agent in the negative electrode active material layer, among the conductive agents described in the description of the positive electrode, a carbon material is preferable, CNT is more preferable, and single-walled carbon nanotubes (SWCNT) are even more preferable. The content of the conductive agent in the negative electrode active material layer may be 0.01% by mass or more and 3% by mass or less, or 0.02% by mass or more and 1% by mass or less. The conductive agent may not be contained in the negative electrode active material layer.

[0064] Among the binders described in the description of the positive electrode, fluororesin, polyacrylate, polymethacrylate, styrene-butadiene rubber, elastomer, etc. are preferably used as the binder in the negative electrode active material layer. However, because these resins are relatively flexible, expansion of the negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum is likely to occur during charging. Therefore, when the binder in the negative electrode active material layer is one of these resins, the advantages of the present invention are more effectively achieved.

[0065] The content of the binder in the negative electrode active material layer is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 8% by mass, and even more preferably 1.5% by mass to 4% by mass.

[0066] The content of the thickener in the negative electrode active material layer may be, for example, 0.1% by mass or more and 6% by mass or less, or 0.5% by mass or more and 3% by mass or less.

[0067] The content of the filler in the negative electrode active material layer may be, for example, 0.1% by mass to 8% by mass, or 0.5% by mass to 5% by mass, 3% by mass or less, or 1% by mass or less, or the negative electrode active material layer may not contain a filler.

[0068] 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.

[0069] The mass per unit area of ​​the negative electrode active material layer is 5 mg / cm ２ 20mg / cm or more ２ Preferably, 8 mg / cm or less ２ 15mg / cm or more ２The following is more preferable. When the mass per unit area of ​​the negative electrode active material layer is equal to or greater than the above lower limit, it is possible to increase the energy density of the nonaqueous electrolyte storage element, etc. When the mass per unit area of ​​the negative electrode active material layer is equal to or less than the above upper limit, it is possible to suppress compression of the separator due to expansion during charging, and it is possible to further reduce the rate of increase in resistance after charge-discharge cycles.

[0070] (Separator) The separator is disposed between the positive electrode and the negative electrode. The separator is usually stacked with one side in contact with the positive electrode and the other side in contact with the negative electrode. The separator is impregnated with a non-aqueous electrolyte. The separator separates the positive electrode and the negative electrode and retains the non-aqueous electrolyte between the positive electrode and the negative electrode.

[0071] The separator can be appropriately selected from known separators that have a creep strain of 0.1 or less after holding a load of 2 MPa at 65°C for 60 seconds and an air permeability resistance of 120 seconds / 100 mL or more and 200 seconds / 100 mL or less. The separator typically has a porous sheet-like substrate layer. The substrate layer of the separator is typically made of resin. "Made of resin" refers to a separator containing resin as the main component. The "main component" refers to a component with a content of 50% by mass or more, preferably 70% by mass or more, and more preferably 90% by mass or more. The separator may consist solely of the substrate layer, or may further have an inorganic layer laminated on the substrate layer. In one embodiment of the present invention, the separator preferably has a substrate layer and an inorganic layer laminated on at least one surface of the substrate layer.

[0072] 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. As the material for the separator substrate layer, polyolefins such as polyethylene, polypropylene, and ethylene-propylene copolymer are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the separator substrate layer. The substrate layer may contain inorganic particles or the like as a component other than the resin. The substrate layer may be a single layer, or may be a multilayer structure of two or more layers (e.g., two to five layers, preferably three layers).

[0073] Known porous resin films used as separator substrate layers include dry porous films produced by a dry process and wet porous films produced by a wet process. The separator used in the nonaqueous electrolyte storage element according to one embodiment of the present invention may be either a dry porous film or a wet porous film. When the separator substrate layer is a dry porous film, its average thickness is preferably relatively large (e.g., 15 μm or more). A wet porous film can be produced by dispersing a pore-forming material (extractable material) such as a plasticizer in a resin such as polyolefin, forming the sheet, extracting the pore-forming material with a solvent or the like to form pores, and optionally performing a stretching process before and / or after the extraction of the pore-forming material. A dry porous film can be produced, for example, by forming a resin into a film and then stretching it (uniaxial or biaxial stretching).

[0074] The upper limit of the porosity of the separator substrate layer is preferably 80 vol%, more preferably 60 vol%, and even more preferably 55 vol% from the viewpoint of strength, etc. The lower limit of the porosity is preferably 20 vol%, more preferably 40 vol%, and even more preferably 45 vol% from the viewpoint of discharge performance, etc. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter. The porosity of the separator substrate layer can be within a range that combines any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0075] The lower limit of the average thickness of the separator substrate layer is preferably 6 μm, more preferably 10 μm, even more preferably 14 μm, and even more preferably 15 μm. When the average thickness of the substrate layer is equal to or greater than the above lower limit, the resistance increase rate of the nonaqueous electrolyte storage element after charge / discharge cycles can be further reduced. The upper limit of the average thickness of the separator substrate layer is preferably 30 μm, more preferably 25 μm, and even more preferably 20 μm. When the average thickness of the substrate layer is equal to or less than the above upper limit, the energy density of the nonaqueous electrolyte storage element can be increased, for example. The average thickness can be within a range that combines any of the above lower limits and any of the above upper limits.

[0076] The inorganic layer of the separator may contain, for example, inorganic particles and a binder. The inorganic layer may be provided on only one surface of the substrate layer, or on both surfaces. In the case of a separator in which the inorganic layer is provided on only one surface of the substrate layer, the separator is preferably disposed between the positive electrode and the negative electrode so that the inorganic layer is in contact with the positive electrode.

[0077] Inorganic particles are particles of inorganic compounds. Examples of inorganic compounds constituting inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; 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, or artificial products thereof. As the inorganic compound, these substances may be used alone or in combination. Among these, silicon oxide, aluminum oxide, and aluminosilicates are preferred.

[0078] Specific examples of the binder for the inorganic layer of the separator include those exemplified as the binder for the positive electrode active material layer.

[0079] The lower limit of the average thickness of the inorganic layer of the separator is preferably 0.5 μm, more preferably 1 μm. On the other hand, the upper limit of the average thickness of the inorganic layer is preferably 10 μm, more preferably 5 μm. By setting the average thickness of the inorganic layer to be equal to or greater than the above lower limit, the heat resistance of the separator can be improved. By setting the average thickness of the inorganic layer to be equal to or less than the above upper limit, the energy density can be increased. The average thickness of the inorganic layer can be within a range combining any of the above lower limits and any of the above upper limits. Note that, when inorganic layers are provided on both sides of the base layer, the above-mentioned average thickness of the inorganic layer refers to the average thickness of each inorganic layer (average thickness per side). The average thickness of the inorganic layer is the average value of thicknesses measured at any five points on the inorganic layer. The average thicknesses of the base layer and the inorganic layer are measured by observing the cross section of the separator using a scanning electron microscope (SEM).

[0080] The average thickness of the separator is preferably 8 μm or more and 30 μm or less, more preferably 12 μm or more and 25 μm or less, and even more preferably 16 μm or more and 20 μm or less. By setting the average thickness of the separator to be equal to or greater than the above lower limit, it is possible to highly reliably suppress short circuits between the positive electrode and the negative electrode. Furthermore, by setting the average thickness of the separator to be equal to or less than the above upper limit, it is possible to increase the energy density, etc. The average thickness of the separator is the average value of thicknesses measured at any five points on the separator.

[0081] The upper limit of the creep strain of the separator after holding a load of 2 MPa at 65°C for 60 seconds is 0.1, preferably 0.09. When the creep strain is equal to or less than the upper limit, compression of the separator is suppressed, thereby reducing the resistance increase rate of the nonaqueous electrolyte energy storage element after charge-discharge cycling. The lower limit of the creep strain may be, for example, 0.01, 0.03, or 0.05. The creep strain may be within a range that combines any of the above lower limits with any of the above upper limits. The creep strain of the separator can be adjusted by the material, porosity, thickness, etc. of the separator (substrate layer and inorganic layer). Typically, a separator with a low creep strain value can be obtained by using a hard material, reducing the porosity, making the inorganic layer relatively thick, etc. The porosity of the substrate layer can be reduced by, for example, reducing the degree of stretching during the production of the substrate layer.

[0082] The lower limit of the separator's air permeation resistance is 120 seconds / 100 mL, or may be 140 seconds / 100 mL. The upper limit of the separator's air permeation resistance is 200 seconds / 100 mL, or may be 195 seconds / 100 mL. When the separator's air permeation resistance is within the above range, the ionic conductivity of the nonaqueous electrolyte contained in the separator's pores is improved, and the resistance increase rate after charge-discharge cycling of the nonaqueous electrolyte storage element can be reduced. The air permeation resistance can be within a range that combines any of the above lower limits and any of the above upper limits. The separator's air permeation resistance can be adjusted by the porosity, thickness, etc. of the separator.

[0083] Thus, the air resistance of the separator is influenced by the physical shape of the separator, whereas the creep strain of the separator is influenced by the physical properties of the separator in addition to the physical shape, and therefore the two are not necessarily linked.

[0084] When the separator has a resin substrate layer, the air resistance of the separator relative to the average thickness of the substrate layer is preferably 15 seconds / (100 mL μm) or less. Furthermore, it is more preferable that the air resistance of the separator relative to the average thickness of the substrate layer is 15 seconds / (100 mL μm) or less and that the air resistance of the separator is 140 seconds / 100 mL or more and 200 seconds / 100 mL or less. In such cases, the ionic conductivity of the nonaqueous electrolyte contained in the separator voids is further optimized, thereby further reducing the resistance increase rate after charge / discharge cycling of the nonaqueous electrolyte storage element. The upper limit of the air resistance of the separator relative to the average thickness of the substrate layer may be 14 seconds / (100 mL μm) or 13 seconds / (100 mL μm). The lower limit of the air permeation resistance of the separator relative to the average thickness of the base layer of the separator is preferably 5 seconds / (100 mL μm), more preferably 8 seconds / (100 mL μm). The air permeation resistance of the separator relative to the average thickness of the base layer of the separator can be within a range that combines any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0085] (Non-aqueous electrolyte) The non-aqueous electrolyte can be appropriately selected from known non-aqueous electrolytes. The non-aqueous electrolyte may be a non-aqueous electrolyte solution. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0086] 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.

[0087] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.

[0088] 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, DMC and EMC are preferred.

[0089] As the non-aqueous solvent, it is preferable to use at least one of a cyclic carbonate and a chain carbonate, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0090] 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.

[0091] The lithium salt is LiPF ６ , LiPO ２ F ２ , LiBF ４ , LiClO ４ , LiN(SO ２ F) ２ inorganic 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.

[0092] 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.

[0093] 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, and the like.In one embodiment of the present invention, a halogenated carbonate ester is preferably used as the additive, and FEC is more preferably used. These additives may be used alone or in combination of two or more.

[0094] 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 cycle performance after high-temperature storage, and further improve safety.

[0095] The non-aqueous electrolyte may be a solid electrolyte, or a non-aqueous electrolytic solution and a solid electrolyte may be used in combination.

[0096] 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, halide solid electrolytes, and polymer solid electrolytes.

[0097] 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.

[0098] The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries, flat batteries, coin batteries, and button batteries.

[0099] Figure 1 shows a nonaqueous electrolyte storage element 1 as an example of a prismatic battery. The figure is a see-through view of the inside of the container. An electrode assembly 2 having a positive electrode and a negative electrode wound with a separator sandwiched between them is housed in a prismatic container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0100] <Electricity Storage Device> The nonaqueous electrolyte energy storage element of the present embodiment can be mounted as an energy storage unit (battery module) comprising a plurality of nonaqueous electrolyte energy storage elements in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), etc., a power source for electronic devices such as a personal computer or a communication terminal, or a power source for power storage, etc. In this case, the technology of the present invention may be applied to at least one nonaqueous electrolyte energy storage element included in the energy storage unit.

[0101] 2 shows an example of an energy storage device 30 in which energy storage units 20, each of which is an assembly of two or more electrically connected nonaqueous electrolyte energy storage elements 1, are further assembled. The energy storage device 30 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte energy storage elements 1, a bus bar (not shown) that electrically connects two or more energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of one or more nonaqueous electrolyte energy storage elements.

[0102] <Method for manufacturing nonaqueous electrolyte storage element> The method for manufacturing the nonaqueous electrolyte storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode assembly, preparing a nonaqueous electrolyte, and housing the electrode assembly and the nonaqueous electrolyte in a container. Preparing the electrode assembly includes 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.

[0103] 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.

[0104] <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.

[0105] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (e.g., a lithium ion secondary battery), but the nonaqueous electrolyte 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.

[0106] 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.

[0107] [Example 1] (Preparation of Positive Electrode) Positive electrode active material (LiNi ３／５ Co １／５ Mn １／５ O ２ A positive electrode mixture paste containing acetylene black (AB) and polyvinylidene fluoride (PVDF) in a mass ratio of 93:4:3 (solids equivalent) and N-methylpyrrolidone (NMP) as a dispersion medium was prepared. This positive electrode mixture paste was applied to one side of an aluminum foil serving as a positive electrode substrate in an amount of 17.4 mg / cm. ２ (solid content equivalent) and dried to obtain a positive electrode.

[0108] (Preparation of Negative Electrode) Silicon oxide (SiO), graphite (Gr), and single-walled carbon nanotubes were mixed in a mass ratio of 5:94.95:0.05 (solid content equivalent) to obtain a mixture containing a negative electrode active material (SiO + Gr). Then, a negative electrode mixture paste containing the above mixture, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in a mass ratio of 97:2:1 (solid content equivalent), and water as a dispersion medium was prepared. This negative electrode mixture paste was applied to one side of copper foil as a negative electrode substrate at a concentration of 9.2 mg / cm. ２ (solid content equivalent) and dried to obtain a negative electrode.

[0109] (Preparation of non-aqueous electrolyte) LiPF 6 as an electrolyte salt was added to a non-aqueous solvent obtained by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 30:35:35. ６ to 1.0 mol / dm ３ Further, fluoroethylene carbonate (FEC) was mixed in an amount of 2 mass % to prepare a non-aqueous electrolyte.

[0110] (Preparation of Separator) A separator was prepared by providing an inorganic layer having an average thickness of 2 μm on one side of a substrate layer which was a wet porous film having an average thickness of 10 μm and a porosity of 44 vol%. The creep strain of this separator after holding a load of 2 MPa at a temperature of 65° C. for 60 seconds was 0.06, and the air permeation resistance of the separator was 125 seconds / 100 mL.

[0111] (Fabrication of non-aqueous electrolyte storage element) An electrode assembly was fabricated by stacking the positive electrode and the negative electrode with the separator interposed therebetween. The separator was disposed between the positive electrode and the negative electrode so that the inorganic layer of the separator was in contact with the positive electrode. This electrode assembly was housed in a case made of a metal resin composite film, and the non-aqueous electrolyte was injected into the case, which was then sealed by thermal welding to obtain the non-aqueous electrolyte storage element of Example 1.

[0112] Examples 2 to 5, Comparative Example 1 Non-aqueous electrolyte storage elements of Examples 2 to 5 and Comparative Example 1 were obtained in the same manner as in Example 1, except that the separators shown in Table 1 were used.

[0113] [Reference Examples 1 and 2] The nonaqueous electrolyte storage elements of Reference Examples 1 and 2 were obtained in the same manner as in Example 1, except that a negative electrode mixture paste containing graphite (Gr), SBR, and CMC in a mass ratio of 97:2:1 (solids equivalent) and using water as a dispersion medium was used, and that a separator shown in Table 1 was used.

[0114] [Evaluation] (Initial Charge / Discharge) Each of the obtained nonaqueous electrolyte storage elements was initially charged and discharged as follows. Constant-current / constant-voltage charging was performed at 25°C with a charging current of 0.2 C, a charge cut-off voltage of 4.25 V, and a total charge time of 8 hours. Subsequently, constant-current discharging was performed with a discharging current of 0.2 C, a discharge cut-off voltage of 2.75 V. Subsequently, constant-current / constant-voltage charging was performed with a charging current of 0.2 C, a charge cut-off voltage of 4.25 V, and a total charge time of 8 hours. Subsequently, constant-current discharging was performed with a discharging current of 0.2 C, a discharge cut-off voltage of 2.75 V. Subsequently, constant-current / constant-voltage charging was performed with a charging current of 0.2 C, a charge cut-off voltage of 4.25 V, and a total charge time of 8 hours. Subsequently, constant-current discharging was performed with a discharging current of 1.0 C, and a discharge cut-off voltage of 2.75 V. A 10-minute rest period was provided between each charge and discharge. The discharge capacity when discharged at a discharge current of 1.0 C was defined as the initial discharge capacity.

[0115] (Initial DC Resistance) After the initial charge and discharge, each nonaqueous electrolyte storage element was charged at a constant current of 1.0 C in a thermostatic chamber at 25 ° C., with a charge current of 50% of the initial discharge capacity, to achieve a 50% SOC. Then, in a thermostatic chamber at -10 ° C., the element was discharged for 60 seconds at discharge currents of 0.1 C, 0.2 C, and 0.3 C, respectively. After each discharge, the element was charged at a constant current of 0.05 C to achieve a 50% SOC. The relationship between the discharge current and the voltage 10 seconds after the start of discharge at each discharge current was plotted, and the DC resistance was calculated from the slope of the straight line obtained from the plot of the three points, which was used as the initial DC resistance.

[0116] (Charge-Discharge Cycle Test) Next, the following charge-discharge cycle test was conducted. In a thermostatic chamber at 45°C, constant current / constant voltage charging was performed with a charging current of 1.0 C and a charge cut-off voltage of 4.25 V. The charge was terminated until the total charge time reached 3 hours. After that, a 10-minute rest period was provided. A constant current discharge was performed with a discharge current of 1.0 C and a discharge cut-off voltage of 2.75 V, followed by a 10-minute rest period. The above charge-discharge cycle was repeated 700 times.

[0117] (Increase in DC Resistance) After the charge-discharge cycle test, the DC resistance of each nonaqueous electrolyte storage element was determined in the same manner as in the above-mentioned "initial DC resistance," and this was used as the DC resistance after the charge-discharge cycle test. The increase in DC resistance after the charge-discharge cycle test was determined from the initial DC resistance and the DC resistance after the charge-discharge cycle test. The increase in DC resistance (DCR increase) is shown in Table 1.

[0118]

[0119] As shown in Table 1, in nonaqueous electrolyte storage elements using silicon oxide as the negative electrode active material, the nonaqueous electrolyte storage elements of Examples 1 to 5, which used separators with a creep strain of 0.1 or less after holding a load of 2 MPa for 60 seconds at 65°C and an air resistance of 120 sec / 100 mL or more and 200 sec / 100 mL or less, had a DCR increase rate of 78% or less, indicating a low resistance increase rate after charge-discharge cycling. Among these Examples, the nonaqueous electrolyte storage elements of Examples 1 to 3 and 5, which used separators with an air resistance relative to the average thickness of the substrate layer of 15 sec / (100 mL μm) or less, had a lower DCR increase rate, and the nonaqueous electrolyte storage elements of Examples 2, 3 and 5, which used separators with an air resistance of 140 sec / 100 mL or more and 200 sec / 100 mL or less, had an even lower DCR increase rate. Furthermore, among the examples, the nonaqueous electrolyte storage elements of Examples 3 and 5, which used separators with substrate layers having an average thickness of 14 μm or more, had particularly low DCR increase rates.

[0120] As shown in Reference Examples 1 and 2, in a nonaqueous electrolyte storage element using only graphite as the negative electrode active material, the DCR increase rate was conversely increased when a separator was used in which the creep strain after holding a load of 2 MPa for 60 seconds at a temperature of 65°C was 0.1 or less and the air resistance was 120 sec / 100 mL or more and 200 sec / 100 mL or less. Although the reason for this is unclear, it is thought that when the negative electrode active material was only graphite, the separator did not compress very much, and instead the use of a separator with a relatively high air resistance caused a significant increase in resistance due to separator clogging.

[0121] The present invention can be applied to nonaqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, automobiles, industrial equipment, and the like.

[0122] REFERENCE SIGNS LIST 1 nonaqueous electrolyte energy storage element 2 electrode body 3 container 4 positive electrode terminal 41 positive electrode lead 5 negative electrode terminal 51 negative electrode lead 20 energy storage unit 30 energy storage device

Claims

1. A non-aqueous electrolyte storage element comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode contains a negative electrode active material containing at least one element selected from the group consisting of silicon, tin, and aluminum, wherein the separator exhibits a creep strain of 0.1 or less after holding a load of 2 MPa at a temperature of 65°C for 60 seconds, and wherein the separator has an air resistance of 120 seconds / 100 mL or more and 200 seconds / 100 mL or less.

2. The nonaqueous electrolyte storage element according to claim 1, wherein the separator has a base layer made of resin, and the air resistance of the separator relative to the average thickness of the base layer is 15 seconds / (100 mL·μm) or less.

3. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the separator has an air resistance of 140 seconds / 100 mL or more and 200 seconds / 100 mL or less.

4. The nonaqueous electrolyte storage element according to claim 1, wherein the separator has a base layer made of resin, and the average thickness of the base layer is 14 μm or more.

5. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the negative electrode has a negative electrode active material layer containing the negative electrode active material, the negative electrode active material being silicon oxide, and the content of the silicon oxide in the negative electrode active material layer is 2% by mass or more and 20% by mass or less.

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