Nonaqueous electrolyte power storage element

Abstract

A nonaqueous electrolyte power storage element according to one aspect of the present invention comprises: a positive electrode that has a positive electrode active material layer; a negative electrode that has a metal negative electrode base material and a negative electrode active material layer which contains graphite; and a separator that is disposed between the positive electrode active material layer and the negative electrode active material layer. The air permeation resistance of the separator is 125 seconds / 100 mL or more, and X represented by formula (1) is 890 or less.　Formula (1): X = PcTcTa / Pa (In formula (1), Pc represents the porosity (%) of the positive electrode active material layer, Tc represents the thickness (μm) of the positive electrode active material layer, Pa represents the porosity (%) of the negative electrode active material layer, and Ta represents the thickness (μm) of the negative electrode active material layer.)

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, typified by lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. In addition to non-aqueous electrolyte secondary batteries, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte energy storage elements.

[0003] A typical nonaqueous electrolyte storage element includes an electrode assembly in which a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material are stacked with a separator interposed therebetween. This electrode assembly is housed in a container together with a nonaqueous electrolyte to form a nonaqueous electrolyte storage element. Carbon materials such as graphite are widely used as the negative electrode active material (see Patent Documents 1 and 2).

[0004] JP 2005-222933 A JP 2017-069039 A

[0005] Graphite, which is a negative electrode active material, undergoes large changes in expansion and contraction during charge and discharge. Large expansion of the negative electrode can easily cause a decrease in ionic conductivity due to compression of the separator adjacent to the negative electrode. The decrease in ionic conductivity due to separator compression can lead to a decrease in the charge and discharge performance of the nonaqueous electrolyte storage element. To prevent this phenomenon, nonaqueous electrolyte storage elements using graphite in the negative electrode often use separators with high air resistance, which are less susceptible to a decrease in ionic conductivity due to compression.

[0006] On the other hand, nonaqueous electrolyte storage elements generally have a set discharge cut-off voltage, and under normal use conditions, once the discharge cut-off voltage is reached, further discharge does not occur. However, if discharge occurs beyond the discharge cut-off voltage due to use in a manner not normally foreseen, overdischarge may occur, resulting in heat generation, etc. The inventors have found that nonaqueous electrolyte storage elements using separators with high air permeability resistance are particularly prone to heat generation during overdischarge tests under specified conditions.

[0007] An object of the present invention is to provide a non-aqueous electrolyte electricity storage element in which heat generation during overdischarge is suppressed.

[0008] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode having a positive electrode active material layer, a negative electrode having a metallic negative electrode substrate and a negative electrode active material layer containing graphite, and a separator disposed between the positive electrode active material layer and the negative electrode active material layer, wherein the separator has an air resistance of 125 seconds / 100 mL or more, and X, represented by the following formula (1), is 890 or less: X=PcTcTa / Pa (1) (In formula (1), Pc is the porosity (%) of the positive electrode active material layer, Tc is the thickness (μm) of the positive electrode active material layer, Pa is the porosity (%) of the negative electrode active material layer, and Ta is the thickness (μm) of the negative electrode active material layer.)

[0009] According to one aspect of the present invention, it is possible to provide a nonaqueous electrolyte electricity storage element in which heat generation during overdischarge is suppressed.

[0010] Fig. 1A is a first schematic diagram illustrating a phenomenon that occurs when a nonaqueous electrolyte electricity storage element is brought into an overdischarged state. Fig. 1B is a second schematic diagram illustrating a phenomenon that occurs when a nonaqueous electrolyte electricity storage element is brought into an overdischarged state. Fig. 1C is a third schematic diagram illustrating a phenomenon that occurs when a nonaqueous electrolyte electricity storage element is brought into an overdischarged state. Fig. 2 is a see-through perspective view showing one embodiment of a nonaqueous electrolyte electricity storage element. Fig. 3 is a schematic diagram showing one embodiment of an electricity storage device formed by assembling a plurality of nonaqueous electrolyte electricity storage elements.

[0011] First, an outline of the nonaqueous electrolyte electricity storage element disclosed in this specification will be described.

[0012] [1] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode having a positive electrode active material layer, a negative electrode having a metallic negative electrode substrate and a negative electrode active material layer containing graphite, and a separator disposed between the positive electrode active material layer and the negative electrode active material layer, wherein the separator has an air resistance of 125 seconds / 100 mL or more, and X, represented by the following formula (1), is 890 or less: X=PcTcTa / Pa (1) (In formula (1), Pc is the porosity (%) of the positive electrode active material layer, Tc is the thickness (μm) of the positive electrode active material layer, Pa is the porosity (%) of the negative electrode active material layer, and Ta is the thickness (μm) of the negative electrode active material layer.)

[0013] The nonaqueous electrolyte storage element described in [1] above suppresses heat generation during overdischarge. While the reason for this is unclear, the following reason is presumed. A phenomenon that occurs when a nonaqueous electrolyte storage element that has reached its end-of-discharge voltage is discharged beyond the end-of-discharge voltage to enter an overdischarge state will be described with reference to FIGS. 1A to 1C . The nonaqueous electrolyte storage element schematically shown in FIGS. 1A to 1C includes a positive electrode 1, a negative electrode 2, and a separator 3. The positive electrode 1 includes a positive electrode substrate 4 and a positive electrode active material layer 5. The negative electrode 2 includes a negative electrode substrate 6 and a negative electrode active material layer 7. The separator 3, the positive electrode active material layer 5, and the negative electrode active material layer 7 are all porous and permeated with a nonaqueous electrolyte (not shown). When the element enters an overdischarge state, the negative electrode potential increases, causing metals constituting the negative electrode substrate 6 to elute as metal ions 8 (see FIG. 1A ). Metal ions 8 eluted from the negative electrode substrate 6 permeate the separator 3 and deposit as metal 9 on the positive electrode 1 (the surface of the positive electrode substrate 4, the surface and pores of the positive electrode active material layer 5, etc.) (see FIG. 1B ). The metal 9 deposited on the positive electrode 1 grows, penetrates the separator 3, and comes into contact with the negative electrode 2, causing an internal short circuit (see FIG. 1C ). If the time until the internal short circuit occurs is long, the temperature inside the nonaqueous electrolyte storage element continues to rise due to Joule heat caused by current flow, and may reach, for example, 140°C or higher. In particular, if the separator 3 has a high air permeability resistance, the metal ions 8 eluted from the negative electrode substrate 6 are less likely to permeate the separator 3, and the metal 9 deposited on the positive electrode 1 is less likely to penetrate the separator 3. This increases the time until the internal short circuit occurs, and the temperature rise is likely to continue. Here, if the porosity (Pa) of the negative electrode active material layer 7 is high and the thickness (Ta) of the negative electrode active material layer 7 is small, the metal ions 8 eluted from the negative electrode substrate 6 easily permeate the negative electrode active material layer 7, thereby shortening the time it takes for the metal ions 8 to reach the positive electrode 1. Furthermore, if the porosity (Pc) of the positive electrode active material layer 5 is low and the thickness (Tc) of the positive electrode active material layer 5 is small, the pores of the positive electrode active material layer 5 are easily filled with the deposited metal 9, and the metal 9 is easily deposited on the surface of the positive electrode substrate 4 or the positive electrode active material layer 5, thereby increasing the rate at which the deposited metal 9 grows from the surface of the positive electrode substrate 4 or the positive electrode active material layer 5 toward the negative electrode 2.That is, it is considered that the smaller the value of X (=PcTcTa / Pa) expressed by the above formula (1), the shorter the time until an internal short circuit occurs. In the nonaqueous electrolyte storage element described in the above [1], since X expressed by the above formula (1) is 890 or less, it is presumed that an internal short circuit is likely to occur in a short time during overdischarge, and heat generation is suppressed.

[0014] "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. Here, the "discharged state" of a carbon material refers to a state in which the carbon material, which is the negative electrode active material, is discharged so that charge-transporting ions capable of being absorbed and released during charging and discharging are sufficiently released. For example, in a half cell using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic lithium as the counter electrode, the open circuit voltage is 0.6 V or more. "Air permeability resistance" is a value measured using the "Gurley tester method" in accordance with JIS-P-8117 (2009). The dimensions of the separator test piece used for the measurement are 50 mm x 50 mm. Furthermore, "air permeability resistance" refers to the average value of the air permeability resistance measured for five separator test pieces. The air permeability resistance of a separator included in a nonaqueous electrolyte energy storage element is measured using a separator obtained from a nonaqueous electrolyte energy storage element disassembled by the following method. First, the nonaqueous electrolyte storage element is discharged to a discharged state (a state in which the nonaqueous electrolyte storage element is discharged at a constant current of 0.1 C to the discharge end voltage during normal use), and then the nonaqueous electrolyte storage element is disassembled in a dry atmosphere. Next, the separator is removed and washed with hydrochloric acid having a concentration of 36% by mass, and then washed with deionized water, and then vacuum dried at room temperature for 10 hours or more. Thereafter, the vacuum-dried separator is cut out to prepare a test piece. The "porosity" of the active material layer (positive electrode active material layer and negative electrode active material layer) is calculated by dividing the apparent volume (volume including voids) of the active material layer by V １ The sum of the actual volumes of the materials constituting the active material layer is V ２ In this case, (1-V ２ / V １ The apparent volume V of the active material layer is calculated by the formula: １can be calculated as the product of the area of ​​the active material layer and the thickness of the active material layer. ２ can be calculated from the content and true density of each material in the active material layer. The "thickness" of the active material layer refers to the thickness of one active material layer. For example, if a positive electrode has a positive electrode substrate and positive electrode active material layers are provided on both sides of the positive electrode substrate, the thickness of the positive electrode active material layer is the thickness of the positive electrode active material layer on one side. The "thickness" of the active material layer refers to the average value of thicknesses measured at any 10 points on the active material layer. The "porosity" and "thickness" of the active material layer are values ​​measured before charge / discharge or in the discharged state of the nonaqueous electrolyte storage element (the state in which the nonaqueous electrolyte storage element is discharged at a constant current of 0.1 C to the discharge end voltage during normal use). Here, "normal use" refers to the use of the nonaqueous electrolyte storage element under the charge / discharge conditions recommended or specified for the nonaqueous electrolyte storage element.

[0015] [2] In the nonaqueous electrolyte storage element according to [1] above, the Pc may be 30% or more and 45% or less, the Tc may be 20 μm or more and 35 μm or less, the Pa may be 40% or more and 55% or less, and the Ta may be 30 μm or more and 45 μm or less.

[0016] In the nonaqueous electrolyte storage element described in [2] above, the effect of suppressing heat generation during overdischarge can be particularly sufficiently achieved.

[0017] [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.

[0018] In general, it is believed that the higher the air permeability resistance of the separator, the more likely it is that heat will be generated during an overdischarge test under specified conditions. Therefore, in the nonaqueous electrolyte storage element described in [3] above, the application of the present invention, which suppresses heat generation during overdischarge, is of great technical significance. Furthermore, in the nonaqueous electrolyte storage element described in [3] above, the ionic conductivity is particularly unlikely to decrease due to separator compression, and therefore, nonaqueous electrolyte storage elements using graphite as the negative electrode active material can exhibit good charge-discharge performance.

[0019] [4] In the nonaqueous electrolyte storage element according to any one of [1] to [3] above, X may be 500 or more and 890 or less. In the nonaqueous electrolyte storage element according to [4] above, the electrodes are less likely to bend during the electrode manufacturing process (e.g., a pressing process), making it possible to obtain a high-quality nonaqueous electrolyte storage element.

[0020] 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.

[0021] <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. At least a portion of 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.

[0022] (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.

[0023] 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 －２The 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).

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

[0025] The 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.

[0026] 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.

[0027] 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 ４Examples 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.

[0028] 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).

[0029] 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.

[0030] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass to 99% by mass, more preferably 70% by mass to 98% by mass, and even more preferably 80% by mass to 95% by mass. By setting the content of the positive electrode active material within the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0031] 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.

[0032] 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.

[0033] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0034] 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 6% by mass, by which the positive electrode active material can be stably maintained.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

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

[0040] The lower limit of the porosity (Pc) of the positive electrode active material layer can be, for example, 20%, but is preferably 30%. The lower limit of Pc may be 32%, 36%, or 40%. By setting Pc to the above lower limit or higher, the reaction area in the positive electrode active material layer becomes sufficiently large, and output performance tends to be improved. The upper limit of Pc can be, for example, 60%, but is preferably 45%. The upper limit of Pc may be 43% or 40%. By setting Pc to the above upper limit or lower, heat generation during overdischarge can be further suppressed. Pc can be set within a range combining any of the above lower limits (however, the lower limit is smaller than the upper limit). The porosity (Pc) of the positive electrode active material layer can be adjusted, for example, by the particle size of the positive electrode active material, the pressure applied to the positive electrode active material layer when producing the positive electrode, etc.

[0041] The lower limit of the thickness (Tc) of the positive electrode active material layer can be, for example, 10 μm, preferably 20 μm, and more preferably 24 μm. By setting Tc to the above lower limit or more, it is possible to increase the energy density per volume of the nonaqueous electrolyte storage element. The upper limit of Tc can be, for example, 50 μm, preferably 35 μm, more preferably 32 μm, and may be 28 μm. By setting Tc to the above upper limit or less, it is possible to further suppress heat generation during overdischarge. Tc can be within a range that combines any of the above lower limits.

[0042] The product of the porosity (Pc) of the positive electrode active material layer and the thickness (Tc) of the positive electrode active material layer (i.e., PcTc) is not particularly limited, but the upper limit of PcTc may be 1500, 1400, 1300, 1200, or 1100. When X is equal to or less than the upper limit, an internal short circuit tends to occur early during overdischarge, and heat generation tends to be more suppressed. The lower limit of PcTc may be, for example, 500, 600, 700, 800, or 900. When PcTc is equal to or greater than the lower limit, the positive electrode is less likely to bend during the positive electrode manufacturing process (e.g., pressing process), and a high-quality positive electrode tends to be obtained. PcTc can be within a range that combines any of the above-mentioned lower limits.

[0043] The positive electrode can be produced, for example, by applying a positive electrode mixture paste to a positive electrode substrate directly or via an intermediate layer, and then drying. After drying, pressing or the like may be performed as necessary. The positive electrode mixture paste contains each component constituting the positive electrode active material layer, such as a positive electrode active material and an optional binder. The positive electrode mixture paste usually further contains a dispersion medium.

[0044] 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.

[0045] The negative electrode substrate is made of metal and has electrical conductivity. Specific examples of the material of the negative electrode substrate include metals such as copper, nickel, stainless steel, and nickel-plated steel, or alloys thereof. Among these, copper or copper alloys are preferred from the viewpoint of high electrical conductivity. When a negative electrode substrate made of copper or a copper alloy is used, the negative electrode substrate usually has a resistance of about 3.5 V vs. Li / Li ＋ In other words, in a non-aqueous electrolyte storage element using graphite as the negative electrode active material and a negative electrode substrate made of copper or a copper alloy, the negative electrode potential rises to about 3.5 V vs. Li / Li due to overdischarge. ＋ When the potential reaches the above levels, copper ions are likely to leach out from the negative electrode substrate. Therefore, when the nonaqueous electrolyte storage element according to one embodiment of the present invention has a negative electrode substrate made of copper or a copper alloy, the effect of the present invention of suppressing heat generation by causing an internal short circuit early during overdischarge is particularly well achieved. Examples of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0046] 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.

[0047] The negative electrode active material layer contains graphite, and optionally contains other negative electrode active materials other than graphite, a conductive agent, a binder, a thickener, a filler, and the like.

[0048] Graphite is a component that functions as a negative electrode active material. Examples of graphite include natural graphite and artificial graphite. From the viewpoint of availability of a material with stable physical properties, artificial graphite is preferred. From the viewpoint of output performance, etc., natural graphite may be preferred in some cases.

[0049] Graphite is usually particulate. The average particle size of graphite is, for example, preferably 1 μm or more and 30 μm or less, more preferably 2 μm or more and 20 μm or less, and even more preferably 4 μm or more and 12 μm or less. By setting the average particle size of the negative electrode active material to the above lower limit or more, the production or handling of the negative electrode active material becomes easy. By setting the average particle size of the negative electrode active material to the above upper limit or less, the electronic conductivity of the negative electrode active material layer improves. In order to obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and classification method can be selected, for example, from the methods exemplified for the positive electrode above.

[0050] The graphite content in the negative electrode active material layer is preferably 60% by mass or more and 99.6% by mass or less, and more preferably 90% by mass or more and 99% by mass or less. The graphite content in the negative electrode active material layer may be 93% by mass or more or 96% by mass or more. By setting the graphite content in the above range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0051] The negative electrode active material layer may contain a negative electrode active material other than graphite. Examples of other negative electrode active materials include non-graphitic carbon, metallic lithium, metals or semimetals such as Si and Sn, metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide, and Li ４ Ti ５ O１２ , LiTiO ２、 TiNb ２ O ７ Examples of the graphite include titanium-containing oxides such as titanium dioxide, polyphosphate compounds, silicon carbide, etc. The content of graphite relative to the total amount of the negative electrode active materials may be 80% by mass or more, 90% by mass or more, 99% by mass or more, 99.9% by mass or more, or 100% by mass.

[0052] The content of the conductive agent in the negative electrode active material layer can be, for example, 0.1% by mass to 5% by mass, and may be 3% by mass or less or 1% by mass or less, or the negative electrode active material layer may not contain a conductive agent.

[0053] The content of the binder in the negative electrode active material layer is preferably 0.5% by mass to 5% by mass, more preferably 0.8% by mass to 3% by mass, and by setting the binder content within the above range, the graphite and the like can be stably held.

[0054] The content of the thickener in the negative electrode active material layer is, for example, preferably 0.1% by mass or more and 6% by mass or less, and more preferably 0.5% by mass or more and 3% by mass or less.

[0055] 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.

[0056] 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.

[0057] The lower limit of the porosity (Pa) of the negative electrode active material layer can be, for example, 30%, preferably 40%, more preferably 42%, and even more preferably 44%. The lower limit of Pa may be 46% or 48%. By setting Pa to the above lower limit or higher, heat generation during overdischarge can be further suppressed. Furthermore, by setting Pa to the above lower limit or higher, the reaction area in the negative electrode active material layer tends to be sufficiently large, and output performance, etc. tends to be improved. The upper limit of Pa can be, for example, 70%, preferably 55%. The upper limit of Pc may be 52%, 50%, or 48%. Pa can be set within a range combining any of the above lower limits and any of the above lower limits (however, the lower limit is smaller than the upper limit). The porosity (Pa) of the negative electrode active material layer may be greater than the porosity (Pc) of the positive electrode active material layer. For example, the porosity (Pa) of the negative electrode active material layer may be 5% or more higher than the porosity (Pc) of the positive electrode active material layer. The porosity (Pa) of the negative electrode active material layer can be adjusted, for example, by the particle size of graphite, the pressure applied to the negative electrode active material layer when producing the negative electrode, etc.

[0058] The lower limit of the thickness (Ta) of the negative electrode active material layer can be, for example, 20 μm, preferably 30 μm, and more preferably 32 μm. By setting Ta to the above lower limit or more, it is possible to increase the energy density per volume of the nonaqueous electrolyte storage element. The upper limit of Ta can be, for example, 60 μm, preferably 45 μm, more preferably 40 μm, and even more preferably 36 μm. The upper limit of Ta may be 34 μm. By setting Ta to the above upper limit or less, it is possible to further suppress heat generation during overdischarge. Ta can be within a range that combines any of the above lower limits.

[0059] The negative electrode can be produced by, for example, applying a negative electrode mixture paste to a negative electrode substrate directly or via an intermediate layer, and then drying. After drying, pressing or the like may be performed as necessary. The negative electrode mixture paste contains each component constituting the negative electrode active material layer, such as graphite and an optional binder. The negative electrode mixture paste usually further contains a dispersion medium.

[0060] (Regarding X Represented by Formula (1)) In a nonaqueous electrolyte storage element according to one embodiment of the present invention, X represented by the following formula (1) is 890 or less. X = PcTcTa / Pa (1) The upper limit of X may be 885, or may be 850, 800, 750, or 700. When X is equal to or less than the upper limit, an internal short circuit tends to occur earlier during overdischarge, and heat generation tends to be further suppressed. The lower limit of X may be, for example, 300, or may be 400, 500, 600, 700, or 800. When X is equal to or greater than the lower limit, the electrode is less likely to bend during the electrode manufacturing process (e.g., a pressing process), and a high-quality nonaqueous electrolyte storage element tends to be obtained. X can be set within a range that combines any of the above-mentioned lower limits and any of the above-mentioned lower limits (provided that the lower limit is smaller than the upper limit). In a preferred embodiment, X may be 400 or more and 890 or less, for example, 500 or more and 890 or less, typically 600 or more and 800 or less.

[0061] (Separator) The separator is disposed between the positive electrode and the negative electrode, specifically between the positive electrode active material layer and the negative electrode active material layer. The positive electrode active material layer and the separator are usually in direct contact with each other. Similarly, the negative electrode active material layer and the separator are usually in direct contact with each other.

[0062] The separator can be appropriately selected from known separators with an air resistance of 125 seconds / 100 mL or more. Examples of separators that can be used include separators consisting of only a substrate layer, and separators in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of the shape of the substrate layer of the separator 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 substrate layer of the separator, polyolefins such as polyethylene and polypropylene 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 substrate layer of the separator.

[0063] Known porous resin films used as separators include dry separators manufactured by a dry process and wet separators manufactured by a wet process. The separator used in a nonaqueous electrolyte storage element according to one embodiment of the present invention may be either a dry separator or a wet separator, but is preferably a dry separator. For example, the separator may be a dry separator that employs dry stretching, in which a resin is formed into a film and then stretched (e.g., uniaxial stretching, in which the resin film is stretched in only one direction at a temperature above the glass transition temperature to orient the molecules). Manufacturing by the dry process has the advantage that the output performance of the nonaqueous electrolyte storage element tends to be improved even when a separator with an air resistance of 125 seconds / 100 mL or more is used.

[0064] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less when heated from room temperature to 500°C under an air atmosphere at 1 atmosphere, and more preferably exhibit a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials exhibiting a mass loss of a predetermined value or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of safety of the nonaqueous electrolyte storage element.

[0065] The lower limit of the separator's air permeability resistance is 125 seconds / 100 mL, preferably 132 seconds / 100 mL, more preferably 140 seconds / 100 mL, and even more preferably 145 seconds / 100 mL. When the separator's air permeability resistance is equal to or greater than the above lower limit, ionic conductivity is less likely to decrease due to compression, making it possible to achieve good charge / discharge performance in a nonaqueous electrolyte storage element using graphite as the negative electrode active material. The upper limit of the separator's air permeability resistance is preferably 250 seconds / 100 mL, more preferably 200 seconds / 100 mL. When the separator's air permeability resistance is equal to or less than the above upper limit, internal short circuits tend to occur more quickly during overdischarge, and heat generation tends to be more suppressed. The separator's air permeability resistance can be within a range that combines any of the above lower limits.

[0066] The thickness of the separator (when a heat-resistant layer is included, the total thickness of the base layer and the heat-resistant layer) is not particularly limited, but the lower limit is preferably 5 μm, more preferably 8 μm. In some embodiments, the thickness of the separator may be, for example, 12 μm or more, typically 15 μm or more (e.g., 18 μm or more). On the other hand, the upper limit of the thickness is preferably 40 μm, more preferably 30 μm. In some embodiments, the thickness of the separator may be, for example, 25 μm or less, typically 22 μm or less. When the thickness of the separator is equal to or greater than the above lower limit and equal to or less than the above upper limit, the above-mentioned effects can be more effectively exhibited. The thickness of the separator can be within a range that combines any of the above lower limits. The "thickness" of the separator refers to the average value of thicknesses measured at any 10 points on the separator.

[0067] (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.

[0068] 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.

[0069] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Of these, EC is preferred.

[0070] 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.

[0071] It is preferable to use a cyclic carbonate or a chain carbonate as the non-aqueous solvent, and it is more preferable to use a cyclic carbonate and a chain carbonate in combination. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of the additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclohexanedicarboxylic anhydride; and ethylene sulfite. Examples of the additives include 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, and tetrakistrimethylsilyl titanate. These additives may be used alone or in combination of two or more.

[0076] 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.

[0077] The non-aqueous electrolyte may be a solid electrolyte, or a non-aqueous electrolytic solution and a solid electrolyte may be used in combination.

[0078] The solid electrolyte can be selected from any material that has ionic conductivity of lithium, sodium, calcium, etc. and is solid at room temperature (e.g., 15° C. to 25° C.) Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and polymer solid electrolytes.

[0079] 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.

[0080] 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.

[0081] Figure 2 shows a nonaqueous electrolyte storage element 10 as an example of a prismatic battery. This figure is a see-through view of the inside of the container. An electrode assembly 11 having a positive electrode and a negative electrode wound with a separator sandwiched between them is housed in a prismatic container 12. The positive electrode is electrically connected to a positive electrode terminal 13 via a positive electrode lead 14. The negative electrode is electrically connected to a negative electrode terminal 15 via a negative electrode lead 16.

[0082] <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.

[0083] 3 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 10, 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 10, 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.

[0084] <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.

[0085] 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.

[0086] <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.

[0087] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (lithium ion secondary battery, etc.), 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.

[0088] 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.

[0089] [Example 1] (Preparation of Positive Electrode) LiNi as a positive electrode active material １／３ Mn １／３ Co １／３ O ２ A positive electrode mixture paste was prepared using acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a dispersion medium. The mass ratio of the positive electrode active material, AB, and PVDF was 93:5:2 (solid content equivalent). The positive electrode mixture paste was applied to both sides of an aluminum foil with an average thickness of 12.0 μm as a positive electrode substrate and dried. Then, roll pressing was performed to obtain a positive electrode in which positive electrode active material layers were laminated on both sides of the positive electrode substrate. The porosity (Pc) of the formed positive electrode active material layer was 37%, and the thickness (Tc) of one layer was 25.0 μm.

[0090] (Preparation of Negative Electrode) A negative electrode mixture paste was prepared using graphite (Gr) as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and water as a dispersion medium. The mass ratio of the negative electrode active material, SBR, and CMC was 98.5:1.0:0.5 (solid content equivalent). The negative electrode mixture paste was applied to both sides of a copper foil with an average thickness of 8.0 μm as a negative electrode substrate and dried. Then, roll pressing was performed to obtain a negative electrode in which a negative electrode active material layer was laminated on both sides of the negative electrode substrate. The porosity (Pa) of the formed negative electrode active material layer was 45%, and the thickness (Ta) of one layer was 32.0 μm.

[0091] (Preparation of non-aqueous electrolyte) LiPF 6 was added to a mixed solvent of 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 The non-aqueous electrolyte was obtained by dissolving the non-aqueous electrolyte at a concentration of 100 ppm.

[0092] (Preparation of Separator) For the separator, a polyolefin microporous film manufactured by a dry method, having an air resistance of 180 seconds / 100 mL and a thickness of 18 μm, was used.

[0093] (Assembly of non-aqueous electrolyte storage element) The positive electrode, negative electrode, and separator were used to obtain a wound electrode assembly. The electrode assembly was placed in a rectangular parallelepiped container, and a non-aqueous electrolyte was poured into the container and sealed to obtain the non-aqueous electrolyte storage element of Example 1.

[0094] [Examples 2 to 4, Comparative Examples 1 to 3, Reference Examples 1 to 5] Nonaqueous electrolyte storage elements of Examples 2 to 4, Comparative Examples 1 to 3, and Reference Examples 1 to 5 were obtained in the same manner as Example 1, except that the porosity and thickness of the positive electrode active material layer and the negative electrode active material layer, the type of negative electrode active material, and the air permeation resistance of the separator were as shown in Table 1. Note that the separators of Examples 1 to 4 and Comparative Examples 1 to 3 were polyolefin microporous membranes manufactured by a dry process. The separators of Reference Examples 1 to 5 were polyolefin microporous membranes manufactured by a wet process. The porosity of the positive electrode active material layer and the negative electrode active material layer was adjusted by the pressure during roll pressing. In Table 1, "Gr" represents graphite, and "HC" represents non-graphitizable carbon. Table 1 also shows the PcTcTa / Pa value for each nonaqueous electrolyte storage element.

[0095] (Evaluation of Curvature) The amount of curvature of each positive electrode was measured under the following conditions. First, a positive electrode before roll pressing was prepared and cut into a piece with a width of 103 mm and a length of 2 m. The positive electrode was roll pressed so that the porosity (Pc) and thickness (Tc) of the positive electrode active material layer were set to predetermined values, and then vacuum-dried in a vacuum dryer at 90 ° C for 12 hours. The cut positive electrode after vacuum drying was placed on a straight 5 m metal ruler so that the longitudinal direction of the positive electrode was roughly parallel to the longitudinal direction of the positive electrode, and one end (corner) and the other end (corner) of the positive electrode in the longitudinal direction were grounded to the metal ruler. At a point 1 m from one end of the positive electrode in the longitudinal direction (i.e., the longitudinal center of the positive electrode), the maximum distance of the gap from the end edge along the longitudinal direction of the metal ruler to the end edge along the longitudinal direction of the positive electrode in the vertical direction was measured as the amount of curvature. Here, the case where the amount of curvature was 10 mm or less was rated A, and the case where the amount of curvature was more than 10 mm was rated B. The results are shown in Table 1.

[0096] (Initial Charge / Discharge) Each of the obtained nonaqueous electrolyte storage elements was initially charged / discharged under the following conditions. In a thermostatic chamber at 25°C, constant current charging was performed with a charging current of 1.0 C and a charge cut-off voltage of 4.10 V, followed by constant voltage charging at 4.10 V. The charge was terminated until the total charge time reached 3 hours. A 10-minute rest period was then provided. Constant current discharge was then performed with a discharge current of 1.0 C and a discharge cut-off voltage of 3.0 V. These charge and discharge processes constitute one cycle, and two cycles were performed. The discharged electrical quantity in the second cycle was taken as the discharge capacity.

[0097] (Overdischarge Test) Next, each nonaqueous electrolyte storage element was overdischarged from a discharged state of 0% SOC to an SOC of -35% by constant current discharge at a discharge current of 1.0 C in a temperature environment of 25°C. The SOC was determined based on the discharge capacity during the initial charge / discharge cycle. The state at which the second cycle of discharge in the initial charge / discharge cycle was completed was defined as a discharged state of 0% SOC, and the state in which an amount of electricity equivalent to the discharge capacity was charged from this state was defined as SOC of 100%. In this overdischarge test, the temperature of the center of the long side of the outer surface of the container of each nonaqueous electrolyte storage element was measured. A case in which heat generation of 140°C or higher did not occur was defined as A, and a case in which heat generation of 140°C or higher occurred was defined as B. The results are shown in Table 1.

[0098]

[0099] As shown in Table 1, in each of the nonaqueous electrolyte storage elements of Comparative Examples 1 to 3, which used graphite as the negative electrode active material, a separator with an air permeability resistance of 125 sec / 100 mL or more, and a PcTcTa / Pa value of more than 890, heat generation of 140°C or more occurred in the overdischarge test. In contrast, in each of the nonaqueous electrolyte storage elements of Examples 1 to 4, which used graphite as the negative electrode active material, a separator with an air permeability resistance of 125 sec / 100 mL or more, and a PcTcTa / Pa value of 890 or less, heat generation of 140°C or more did not occur in the overdischarge test. Furthermore, it was confirmed that in each of the nonaqueous electrolyte storage elements of Examples 1 to 3, which had a PcTcTa / Pa value of 500 or more and 890 or less, high-quality nonaqueous electrolyte storage elements in which electrode curvature was suppressed were obtained. In each of the nonaqueous electrolyte storage elements of Reference Examples 1 to 5, which used a separator with an air permeation resistance of less than 125 seconds / 100 mL, heat generation of 140°C or higher did not occur in the overdischarge test, regardless of whether the negative electrode active material was graphite or non-graphitizable carbon. It was confirmed that heat generation of 140°C or higher during the overdischarge test is a phenomenon that is particularly pronounced in nonaqueous electrolyte storage elements which use graphite as the negative electrode active material and a separator with an air permeation resistance of 125 seconds / 100 mL or higher.

[0100] The present invention can be applied to nonaqueous electrolyte electricity storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles.

[0101] REFERENCE SIGNS LIST 1 positive electrode 2 negative electrode 3 separator 4 positive electrode substrate 5 positive electrode active material layer 6 negative electrode substrate 7 negative electrode active material layer 8 metal ion 9 metal 10 non-aqueous electrolyte storage element 11 electrode body 12 container 13 positive electrode terminal 14 positive electrode lead 15 negative electrode terminal 16 negative electrode lead 20 storage unit 30 storage device

Claims

1. A non-aqueous electrolyte storage element comprising: a positive electrode having a positive electrode active material layer; a negative electrode having a metallic negative electrode substrate and a negative electrode active material layer containing graphite; and a separator disposed between the positive electrode active material layer and the negative electrode active material layer, wherein the separator has an air resistance of 125 seconds / 100 mL or more; and X, represented by the following formula (1), is 890 or less: X=PcTcTa / Pa (1) (In formula (1), Pc is the porosity (%) of the positive electrode active material layer, Tc is the thickness (μm) of the positive electrode active material layer, Pa is the porosity (%) of the negative electrode active material layer, and Ta is the thickness (μm) of the negative electrode active material layer.) 2. The nonaqueous electrolyte storage element according to claim 1, wherein Pc is 30% or more and 45% or less, Tc is 20 μm or more and 35 μm or less, Pa is 40% or more and 55% or less, and Ta is 30 μm or more and 45 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.

4. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the X is 500 or more and 890 or less.

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