Energy storage element

Abstract

An electric power storage element according to one aspect of the present invention is provided with a positive electrode containing a positive electrode active material and a conducting agent, a negative electrode containing a negative electrode active material, and a separator interposed between the negative electrode and the positive electrode. The content of the conducting agent in the positive electrode is 6 wt% or less, the positive electrode active material includes a polyanion compound, the negative electrode active material includes a carbon material, the separator has a base material layer composed of a porous polyolefin resin film, the base material layer includes inorganic particles, and the separator has an air permeability per unit thickness of 4.0 sec / (100 cm3･μm).

Description

[Technical Field]

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

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

[0003] To increase the capacity and improve the energy density of such energy storage elements, carbon materials such as graphite are used as the negative electrode active material of the above-mentioned energy storage elements (see Patent Document 1).Furthermore, as the separator of this type of energy storage element, a polyolefin-based porous film with a large number of pores formed therein is used to ensure ion permeability between the positive and negative electrodes (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2005-222933 [Patent Document 2] International Publication No. 2012 / 049748 Summary of the Invention [Problem to be solved by the invention]

[0005] However, energy storage devices using conventional carbon materials as negative electrode active materials have a problem of insufficient output performance. Furthermore, in recent years, energy storage devices have been used as engine-assist power sources for hybrid vehicles and plug-in hybrid vehicles. Energy storage devices used in this type of automotive field are required to have excellent output characteristics and high resistance to internal short circuits.

[0006] An object of the present invention is to provide an energy storage element that uses a carbon material as a negative electrode active material, and that has excellent output performance and high resistance to internal short circuits. [Means for solving the problem]

[0007] An electric storage element according to one aspect of the present invention includes a positive electrode containing a positive electrode active material and a conductive agent, a negative electrode containing a negative electrode active material, and a separator interposed between the negative electrode and the positive electrode, wherein the content of the conductive agent in the positive electrode is 6 mass % or less, the positive electrode active material contains a polyanionic compound, the negative electrode active material contains a carbon material, the separator has a substrate layer made of a porous polyolefin resin film, the substrate layer contains inorganic particles, and the separator has an air permeability per unit thickness of 4.0 sec / (100 cm 3 ·μm or less. [Effects of the Invention]

[0008] An energy storage device according to one aspect of the present invention has excellent output performance and high resistance to internal short circuits. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view showing an embodiment of an energy storage element. [Figure 2] FIG. 2 is a schematic diagram showing an embodiment of an electricity storage device configured by assembling a plurality of electricity storage elements. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention provides the following aspects.

[0011] Section 1. a positive electrode containing a positive electrode active material and a conductive agent; a negative electrode containing a negative electrode active material; a separator interposed between the negative electrode and the positive electrode; Equipped with the content of the conductive agent in the positive electrode is 6% by mass or less, the positive electrode active material contains a polyanionic compound, the negative electrode active material contains a carbon material, the separator has a substrate layer made of a porous polyolefin-based resin film, the substrate layer contains inorganic particles, The air permeability per unit thickness of the separator is 4.0 seconds / (100cm 3 A storage element having a diameter of 1 / 4 μm or less.

[0012] Section 2. Item 2. The electric storage element according to item 1, wherein the separator has an average thickness of 18 μm or less.

[0013] Section 3. Item 3. The electric storage element according to item 1 or 2, wherein the separator has a porosity of 58% or less.

[0014] Section 4. Item 4. The electric storage device according to any one of items 1 to 3, wherein the polyanionic compound has an average particle size of 5 μm or less.

[0015] An electric storage element according to one aspect of the present invention includes a positive electrode containing a positive electrode active material and a conductive agent, a negative electrode containing a negative electrode active material, and a separator interposed between the negative electrode and the positive electrode, wherein the content of the conductive agent in the positive electrode is 6 mass % or less, the positive electrode active material contains a polyanionic compound, the negative electrode active material contains a carbon material, the separator has a substrate layer made of a porous polyolefin resin film, the substrate layer contains inorganic particles, and the separator has an air permeability per unit thickness of 4.0 sec / (100 cm 3 ·μm or less.

[0016] The present inventors have developed a storage element using a carbon material as the negative electrode active material, in which the base layer contains inorganic particles and the air permeability per unit thickness is 4.0 sec / (100 cm 3 It has been found that by combining a separator having a particle size of 0.1 μm or less with a polyanionic compound as the positive electrode active material, and by setting the content of the conductive agent in the positive electrode to 6 mass % or less, it is possible to improve the output performance and resistance to internal short circuits of the energy storage element (for example, suppress temperature rise). The reason for this is unclear, but it is thought to be as follows. In polyanionic compounds, the oxygen elimination reaction from the crystal lattice does not easily proceed, so the temperature rise in the energy storage element when an internal short circuit occurs can be suppressed. Furthermore, by setting the content of the conductive agent in the positive electrode to 6 mass % or less, the short circuit current when an internal short circuit occurs in the energy storage element can be prevented from becoming too large, thereby enhancing the effect of suppressing the temperature rise when an internal short circuit occurs in the energy storage element. On the other hand, when the air permeability per unit thickness of the separator is 4.0 sec / (100 cm 3By having a particle size of 0.1 μm or less, the diffusibility of charge carriers (lithium ions in the case of lithium ion secondary batteries) from the positive electrode containing a polyanionic compound can be improved. Furthermore, by containing inorganic particles in the separator substrate layer, it is possible to maintain the shape of the separator and sufficiently reduce the air permeability of the separator, even if the separator is subjected to strong pressure due to the expansion and contraction of the negative electrode containing a carbon material. Furthermore, the heat resistance of the separator is improved, and the effect of suppressing temperature rise in the event of an internal short circuit in the storage element can be improved. Therefore, it is presumed that the storage element has excellent output performance and high resistance to internal short circuits. Here, "air permeability" is also known as the Gurley value, and indicates the number of seconds it takes for a certain volume of air to pass through a certain area of ​​paper under a certain pressure difference, and is a value measured in accordance with JIS-P-8117 (2009).

[0017] The average thickness of the separator is preferably 18 μm or less. By making the average thickness of the separator 18 μm or less, output performance can be further improved. The average thickness of the separator is the average value of thicknesses measured at any 10 points.

[0018] The porosity of the separator is preferably 58% or less. By having the porosity of the separator be 58% or less, it is possible to further improve resistance to internal short circuits while maintaining good output characteristics. The porosity is the ratio of the void volume to the total volume of the separator, and is measured in accordance with the "pore volume ratio" specified in JIS-L-1096 (2010).

[0019] The polyanionic compound preferably has an average particle size of 5 μm or less, which can further improve output performance.

[0020] The configuration of an energy storage element, the configuration of an energy storage device, and a method for manufacturing an energy storage element according to one embodiment of the present invention, as well as 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] <Configuration of energy storage element> An energy 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 for accommodating the electrode assembly and the non-aqueous electrolyte. The electrode assembly is typically a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with separators interposed therebetween, or a wound type in which a stack of positive electrodes and negative electrodes is wound with a separator interposed therebetween. The non-aqueous electrolyte is present in a state contained in the positive electrode, negative electrode, and separator. As an example of an energy storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as a "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 is electrically conductive. Whether or not it has "electrical conductivity" is determined by whether the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7 The threshold value is Ω·cm. The material of the positive electrode substrate is a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy of these. Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high conductivity, and cost. Positive electrode substrates include foils, vapor-deposited films, meshes, and porous materials, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[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 secondary battery.

[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 a conductive agent, and optionally contains a binder, a thickener, a filler, and other optional components, as needed.

[0027] The positive electrode active material includes a polyanion compound capable of absorbing and releasing ions such as lithium ions. The polyanion compound includes an oxoacid anion (PO4 3- , SO4 2- , SiO4 4- , BO3 3- , VO4 3- Oxo acid anions include compounds containing condensed anions (P2O7 4- , P3O 10 5- The polyanionic compound preferably contains an alkali metal element or alkaline earth metal element and a transition metal element. The polyanionic compound may further contain other elements (e.g., halogen elements, etc.). As the alkali metal element or alkaline earth metal element contained in the polyanionic compound, alkali metal elements are preferred, with lithium, sodium, and potassium being more preferred, and lithium being even more preferred. As the transition metal element contained in the polyanionic compound, iron, manganese, nickel, and cobalt are preferred, with iron being more preferred. As the oxo acid anion contained in the polyanionic compound, phosphate anion (PO4 3- ) and silicate anion (SiO4 4- ) is preferred, and phosphate anion (PO4 3- ) is more preferred.

[0028] A preferred example of the polyanionic compound disclosed herein is a compound represented by the following formula 1: Lia M b (AO c ) d X e ···1 In Formula 1, M is at least one transition metal element. A is at least one selected from B, Al, Si, P, S, Cl, Ti, V, Cr, Mo, and W. X is at least one halogen element. a, b, c, d, and e are numbers satisfying 0 < a ≤ 3, 0 < b ≤ 2, 2 ≤ c ≤ 4, 1 ≤ d ≤ 3, and 0 ≤ e ≤ 1. a, b, c, d, and e may all be integers or may be decimals.

[0029] As M in Formula 1, any one of Fe, Mn, Ni, or Co, or a combination of two or more of these is preferable, and those with a high content rate of such elements (for example, those containing 50 mol% or more of Fe or Mn in M) are suitable. Among these, Fe or Mn, or a combination of two types of Fe and Mn is preferable, and in particular, it is preferable that M is only Fe or the content rate of Fe is high. As A, P or Si is preferable, and in particular, P is preferable. As X, F is preferable. As one embodiment, a = 1, b = 1, c = 4, d = 1, and e = 0 may be preferable in some cases. The technology disclosed herein can be preferably implemented in an aspect where the polyanion-based compound contains at least one of Fe, Mn, Ni, and Co. Note that the above formula showing the polyanion-based compound indicates the composition in the state before the first charging process (that is, the charging process performed for the first time after assembling the power storage element with components such as a positive electrode, a negative electrode, and an electrolyte).

[0030] Specific examples of the polyanion-based compound include, for example, LiFePO4, LiCoPO4, LiFe 0.5 Co 0.5 PO4, LiMnPO4, LiNiPO4, LiMn 0.5 Fe 0.5 PO4, LiCrPO4, LiFeVO4, Li2FeSiO4, Li2Fe2(SO4)3, LiFeBO3, LiFePO 3.9 F 0.2, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. The atoms or polyanions in these polyanionic compounds may be partially substituted with other atoms or polyanions. The surface of the polyanionic compound may be coated with other materials (e.g., carbonaceous materials such as graphite and non-graphitic carbon). One type of polyanionic compound may be used alone, or two or more types may be used in combination.

[0031] The polyanionic compound is usually in the form of particles (powder). The average particle size of the polyanionic compound is not particularly limited, but may be, for example, 0.1 μm to 20 μm. The average particle size of the polyanionic compound is preferably 1 μm to 15 μm, more preferably 1.5 μm to 10 μm, and even more preferably 2 μm to 5 μm. By setting the average particle size of the polyanionic compound to be equal to or greater than the above-mentioned lower limit, the production or handling of the polyanionic compound becomes easier. By setting the average particle size of the polyanionic compound to be equal to or less than the above-mentioned upper limit, the electronic conductivity of the positive electrode active material layer is improved, and the output performance of the energy storage device is further improved. From the viewpoint of improving the output performance of the energy storage device, the average particle size of the polyanionic compound is preferably approximately 5 μm or less (for example, 4 μm or less, typically 3.5 μm or less). The average particle size of the polyanionic compound may be equal to or greater than any of the above-mentioned lower limits and equal to or less than any of the above-mentioned upper limits. When a composite of a polyanionic compound and another material (e.g., a carbonaceous material such as graphite or non-graphitic carbon) 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 of particles diluted with a solvent in accordance with JIS-Z-8825 (2013).

[0032] 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.

[0033] The specific surface area of ​​the polyanionic compound is not particularly limited, but is preferably 5 m 2 The specific surface area of ​​the polyanionic compound can be 8 m / g or more. 2 / g or more is preferable, and 10m 2 / g or more is more preferable, and 12m 2 / g or more (e.g., 14.0m 2 / g or more, e.g., 15.0m 2 / g or more). By making the specific surface area of ​​the polyanionic compound equal to or greater than the lower limit, the input performance of the secondary battery is further improved. The specific surface area of ​​the polyanionic compound is 30 m 2 / g or less, and 2 / g or less. The specific surface area of ​​the polyanionic compound may be equal to or greater than any of the above-mentioned lower limits and equal to or less than any of the above-mentioned upper limits. The "specific surface area" of the polyanionic compound is a value measured in accordance with JIS-Z-8830 (2013).

[0034] The content of the polyanionic compound 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 polyanionic compound within this range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0035] The positive electrode active material layer may further contain a positive electrode active material other than a polyanionic compound (hereinafter referred to as a non-polyanionic positive electrode active material). Such a non-polyanionic positive electrode active material can be appropriately selected from known positive electrode active materials commonly used in lithium ion secondary batteries and the like. Examples of non-polyanionic positive electrode active materials include lithium transition metal composite oxides (lithium nickel cobalt manganese composite oxides) having an α-NaFeO2 crystal structure, lithium transition metal composite oxides having a spinel crystal structure, chalcogen compounds, sulfur, etc. Examples of lithium transition metal composite oxides having an α-NaFeO2 crystal structure include Li[Li x Ni (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Co (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Mn (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Ni γ Mn β Co (1-x-γ-β) ]O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), Li[Li x Ni γ Co β Al (1-x-γ-β) ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1). Lithium transition metal composite oxides with spinel crystal structure include Li x Mn2O4, Li x Ni γ Mn (2-γ) Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. Some of the atoms in these materials may be substituted with atoms of other elements.

[0036] The lower limit of the content of the polyanionic compound relative to the total positive electrode active material contained in the positive electrode active material layer is 50% by mass. The lower limit of the content of the polyanionic compound is preferably 60% by mass, more preferably 80% by mass, even more preferably 90% by mass, and particularly preferably 99% by mass. The content of the polyanionic compound relative to the total mass of the positive electrode active material may be, for example, 100% by mass. By using substantially only the polyanionic compound as the positive electrode active material in this way, the above-mentioned performance improvement effect (for example, the effect of improving resistance to internal short circuits) can be further enhanced.

[0037] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent may be in the form of powder or fiber. As the conductive agent, one of these materials may be used alone, or two or more may be mixed. These materials may also be used in combination. For example, a composite of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred.

[0038] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more, more preferably 3% by mass or more. By setting the content of the conductive agent to be equal to or greater than the above-mentioned lower limit, the energy density of the secondary battery can be increased. From the viewpoint of improving resistance to internal short circuits, the content of the conductive agent is 6% by mass or less (for example, 1% by mass or more and 6% by mass or less), and preferably 5% by mass or less (for example, 2% by mass or more and 5% by mass or less). The content of the conductive agent may be equal to or greater than any of the above-mentioned lower limits and equal to or less than any of the above-mentioned upper limits. Note that the content of the conductive agent does not include carbonaceous materials, etc., that coat the surface of the polyanionic compound.

[0039] 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.

[0040] The binder content in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the binder content within this range, the active material can be stably held.

[0041] 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.

[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 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, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0044] (Negative electrode) 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 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.

[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 secondary battery.

[0047] The negative electrode active material layer contains a negative electrode active material.

[0048] The negative electrode active material includes a carbon material capable of absorbing and releasing ions such as lithium ions. By including a carbon material as the negative electrode active material, the volumetric energy density of the energy storage element can be increased, and output performance can be improved.

[0049] Examples of carbon materials include graphite and non-graphitic carbon. Examples of non-graphitic carbon include non-graphitic carbon (hard carbon), graphitic carbon (soft carbon), and amorphous carbon. Among these materials, graphite, non-graphitic carbon, and graphitic carbon are preferred. Of these, graphite is particularly preferred. A negative electrode containing graphite undergoes significant expansion and contraction during charging and discharging, which tends to subject the separator to strong pressure due to the expansion and contraction. However, this embodiment can suppress the inconvenience caused by such pressure. The carbon material may be composite particles formed by combining the carbon material with particles of another material (e.g., another carbon material or a Si compound), or may be non-composite particles. For example, the particles made of the carbon material may have a coating (e.g., an amorphous carbon coating) on ​​their surfaces. In the negative electrode active material layer, one of these materials may be used alone, or two or more may be used in combination.

[0050] "Graphite" refers to graphite 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. Here, natural graphite is a general term for graphite extracted from natural minerals, and artificial graphite is a general term for graphite produced artificially. Specific examples of natural graphite include massive graphite, flaky graphite, and amorphous graphite. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

[0051] "Non-graphitic carbon" refers to the carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Examples of non-graphitic 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.

[0052] Here, the "discharged state" refers to a state in which the negative electrode active material, a carbonaceous material, is discharged so that lithium ions capable of being absorbed and desorbed during charging and discharging are sufficiently released. For example, in a single-electrode battery using a negative electrode containing a carbonaceous material as a negative electrode active material as a working electrode and metallic Li as a counter electrode, this refers to a state in which the open circuit voltage is 0.7 V or higher.

[0053] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0054] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0055] The carbon material is usually in the form of particles (powder). The average particle size of the carbon material is not particularly limited, but can be, for example, 1 nm to 100 μm. The average particle size of the carbon material is preferably 1 μm to 50 μm, more preferably 1.2 μm to 25 μm, and even more preferably 1.5 μm to 10 μm (e.g., 5 μm or less). By setting the average particle size of the carbon material to be equal to or greater than the above lower limit, the carbon material can be easily produced or handled. By setting the average particle size of the carbon material to be equal to or less than the above upper limit, the electronic conductivity of the active material layer is improved. To obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and classification method can be selected, for example, from the methods exemplified for the positive electrode above.

[0056] The content of the carbon material (negative electrode active material) in the negative electrode active material layer is preferably 60% by mass to 99% by mass, more preferably 90% by mass to 98% by mass. By setting the carbon material content within this range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0057] The negative electrode active material layer may contain other negative electrode active materials in addition to the carbon materials described above, provided that the effects of the present invention are not impaired. Examples of such other negative electrode active materials include metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 Examples of suitable oxides include titanium-containing oxides such as LiTiO2 and TiNb2O7; polyphosphate compounds; and silicon carbide.

[0058] The proportion of the carbon material content relative to the total mass of the negative electrode active material contained in the negative electrode active material layer is preferably greater than 50% by mass. The lower limit of the carbon material content relative to the total mass of the negative electrode active material is preferably 60% by mass, more preferably 70% by mass. For example, the carbon material content relative to the total mass of the negative electrode active material may be, for example, 80% by mass or more, typically 90% by mass or more. By setting the carbon material content to the lower limit or more, it is possible to further improve output performance. On the other hand, the upper limit of the carbon material content relative to the total mass of the negative electrode active material may be, for example, 100% by mass. By using substantially only a carbon material as the negative electrode active material in this way, it is possible to further enhance the performance improvement effect described above.

[0059] The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as needed. Examples of the conductive agent include carbonaceous materials other than the negative electrode active material, metals, and conductive ceramics. The optional components such as the binder, thickener, and filler can be selected from the materials exemplified for the positive electrode.

[0060] 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.

[0061] (separator) The separator is interposed between the negative electrode and the positive electrode. The separator has a substrate layer. The substrate layer is composed of a porous polyolefin-based resin film and contains inorganic particles. Examples of polyolefin-based resins constituting the substrate layer include polyethylene (PE) and polypropylene (PP). Among these, polyethylene-based resins are preferred. As the polyethylene-based resin, an ethylene homopolymer or an ethylene copolymer is preferably used. As the ethylene copolymer, a resin containing 30% by mass or more (e.g., 50% by mass or more) of repeating units derived from ethylene can be used, such as a copolymer obtained by polymerizing an olefin copolymerizable with ethylene or a copolymer obtained by polymerizing at least one monomer copolymerizable with ethylene. Examples of olefins copolymerizable with ethylene include propylene. Examples of other monomers include conjugated dienes (e.g., butadiene) and acrylic acid. Substrate layers containing these polyolefin-based resins are preferred because of their excellent shutdown function. Furthermore, a uniaxially or biaxially stretched porous resin film can be suitably used as the substrate layer of the separator. Among these, biaxially stretched resin films are preferred. Here, "uniaxial stretching" refers to stretching a resin film only in one direction (e.g., the longitudinal direction) in a process of stretching the resin film at or above its glass transition temperature to orient the molecules, while "biaxial stretching" refers to stretching in two orthogonal directions (e.g., the longitudinal direction and the width direction). The width direction refers to a direction parallel to the conveying surface of the resin film and perpendicular to the longitudinal direction. Furthermore, the method of making the separator substrate layer porous in the manufacturing process is not particularly limited. For example, a dry substrate layer employing dry stretching (e.g., uniaxial stretching) after drying, or a wet substrate layer employing wet stretching (e.g., biaxial stretching) in a wet state (e.g., a state in which the raw material resin, inorganic particles, and a solvent are mixed) can be used. Among these, a wet-stretched substrate layer is preferred. A composite material of these resins or a mixture of two or more types may be used as the separator substrate layer.For example, the structure of the base layer may be a single-layer structure, a mixed structure (e.g., a mixed structure of PP and PE), or a multi-layer structure (e.g., a three-layer structure of PP / PE / PP or a two-layer structure of PP / PE). Of these, a single-layer structure of PE or a mixed structure of PP and PE is particularly preferred.

[0062] The substrate layer contains inorganic particles. By including inorganic particles in the substrate layer of the separator, the separator can maintain its shape and the resistance to internal short circuits can be improved by enhancing the effect of suppressing temperature rise when a short circuit occurs in the energy storage element. In this embodiment, the substrate layer includes a porous polyolefin resin film and inorganic particles dispersed in the resin film. In a preferred aspect, the inorganic particles are held in the voids of the resin film.

[0063] Examples of inorganic particles contained in the substrate layer include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; 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 compounds thereof. As the inorganic compound, these substances may be used alone or in combination as a complex, or two or more types may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, and aluminosilicates are preferred from the viewpoint of enhancing the resistance of the energy storage device to internal short circuits.

[0064] The content of inorganic particles contained in the base layer is preferably 1% by mass to 90% by mass, more preferably 5% by mass to 85% by mass. By ensuring that the content of inorganic particles is within this range, it is possible to improve resistance to internal short circuits and output performance. Furthermore, by ensuring that the content of inorganic particles is within this range, it is possible to achieve an optimal balance between strength (pressure resistance in the thickness direction), flexibility, tear resistance, etc.

[0065] The average particle size of the inorganic particles contained in the substrate layer is not particularly limited. The average particle size of the inorganic particles can be, for example, 0.01 μm or more and 10 μm or less. The average particle size of the inorganic particles is preferably 0.05 μm or more and 5 μm or less, and more preferably 0.1 μm or more and 1 μm or less. In some embodiments, the average particle size of the inorganic particles may be 0.8 μm or less, or may be 0.5 μm or less. The average particle size of the inorganic particles may be larger or smaller than the average pore size of the resin film, but is preferably smaller than the average pore size of the resin film.

[0066] The upper limit of the air permeability per unit thickness of the separator is 4.0 sec / (100 cm 3 μm), and 3.9 sec / (100 cm 3 ·μm), 3.8 sec / (100cm 3 ·μm) is more preferable. By setting the upper limit of the separator's air permeability per unit thickness to the above upper limit or less, output performance can be improved. On the other hand, the lower limit of the separator's air permeability per unit thickness is set to 2.0 sec / (100 cm) from the viewpoint of maintaining the separator's strength. 3 ·μm), 2.5 sec / (100cm 3 In some embodiments, the separator has an air permeability per unit thickness of, for example, 2.8 seconds / (100 cm 3 ≈μm) or more, typically 3.0 sec / (100 cm 3 The air permeability per unit thickness of the separator may be equal to or greater than any of the lower limits described above and equal to or less than any of the upper limits described above. The technology disclosed herein is a separator having an air permeability per unit thickness of 2.0 sec / (100 cm 3·μm) or more 4.0 seconds / (100cm 3 μm) or less, even 2.5 seconds / (100cm 3 ·μm) or more 3.8 seconds / (100cm 3 The separator can be preferably implemented in an embodiment in which the air permeability per unit thickness is (μm) or less. When the separator has an air permeability per unit thickness within the above range, both output performance and resistance to internal short circuits can be achieved at a higher level. The air permeability per unit thickness of the separator can be adjusted by the porosity of the separator, the content of inorganic particles, etc.

[0067] The average thickness of the separator is not particularly limited. The upper limit of the average thickness of the separator is, for example, 30 μm. The average thickness of the separator is, for example, preferably 25 μm or less, more preferably 20 μm or less, and even more preferably 18 μm. In some embodiments, the average thickness of the separator may be 16 μm or less (e.g., 15 μm or less), or may be 12 μm or less (e.g., 10 μm or less). By setting the average thickness of the separator to the above upper limit or less, the output performance of the energy storage device can be further improved. On the other hand, the lower limit of the average thickness of the separator is preferably 1 μm, more preferably 3 μm, and more preferably 5 μm. In some embodiments, the average thickness of the separator may be 6 μm or more, or may be 9 μm or more. By setting the average thickness of the separator to the above lower limit or more, sufficient insulation properties and mechanical strength can be achieved. The average thickness of the separator may be equal to or greater than any of the above lower limits and equal to or less than any of the above upper limits. The technology disclosed herein can be preferably implemented in an embodiment in which the average thickness of the separator is 3 μm or more and 20 μm or less, and further 5 μm or more and 18 μm or less. When the average thickness of the separator is within the above range, output performance and resistance to internal short circuits can be achieved at a higher level.

[0068] The porosity of the separator is not particularly limited. The upper limit of the porosity of the separator is, for example, 70%. The porosity of the separator is, for example, preferably 68% or less, more preferably 65% ​​or less, and even more preferably 62% or less. In some embodiments, the porosity of the separator may be 60% or less, or may be 58% or less. By setting the porosity to the upper limit or less, the strength of the separator can be maintained at a good level. On the other hand, the lower limit of the porosity is preferably 40%, more preferably 45%, even more preferably 50%, and particularly preferably 52%. By setting the porosity to the lower limit or more, the reliability of the energy storage element can be further improved while maintaining good output characteristics. The porosity of the separator may be equal to or greater than any of the lower limits and equal to or less than any of the upper limits. The technology disclosed herein can be preferably implemented in an embodiment in which the porosity of the separator is 40% to 65%, or even 50% to 58%. When the porosity of the separator is within the above range, both output performance and resistance to internal short circuits can be achieved at a higher level.

[0069] The air permeability of the entire separator is 4.0 seconds / (100cm) per unit thickness. 3 There are no particular limitations as long as the separator has an air permeability of, for example, 80 sec / (100 cm 3 The air permeability of the entire separator is preferably 70 sec / (100 cm 3 ) or less, more preferably 60 seconds / (100cm 3 In some embodiments, the air permeability of the entire separator is, for example, 55 sec / (100 cm 3 ) or less, and 3 ) or less (e.g. 45 seconds / (100cm 3 On the other hand, the air permeability of the entire separator is preferably 20 sec / (100 cm) or less from the viewpoint of maintaining the strength of the separator. 3 ) or more is preferable, and 25 seconds / (100cm 3 In some embodiments, the air permeability of the entire separator is, for example, 30 sec / (100 cm 3) or more, 35 seconds / (100cm 3 The air permeability of the entire separator may be equal to or greater than any of the lower limits and equal to or less than any of the upper limits. The technology disclosed herein is a separator having an air permeability of 20 sec / (100 cm 3 ) or more 80 seconds / (100cm 3 ) or less, or even 25 seconds / (100cm 3 ) or more 60 seconds / (100cm 3 ) or less (e.g. 60 seconds / (100cm 3 ), typically less than 55 seconds / (100cm 3 When the air permeability of the entire separator is within the above range, both output performance and resistance to internal short circuits can be achieved at a higher level.

[0070] The separator may have a heat-resistant layer on a base layer made of a polyolefin resin film. The heat-resistant layer may contain, for example, heat-resistant particles and a binder. The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere, and more preferably have a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials that have a mass loss of a predetermined amount 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 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; and mineral-derived substances or artificial products thereof such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica. As inorganic compounds, these substances may be used alone or in combination. Two or more of these substances may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, boehmite, and aluminosilicates are preferred from the viewpoint of the safety of the energy storage device.

[0071] The separator may not have the heat-resistant layer on the base layer made of a polyolefin resin film. The separator has an air permeability per unit thickness of 4.0 sec / (100 cm 3 The technique disclosed herein can be preferably implemented in an embodiment in which the heat-resistant layer is not provided on a substrate layer made of a polyolefin resin film.

[0072] (non-aqueous electrolyte) The nonaqueous electrolyte can be appropriately selected from known nonaqueous electrolytes. The nonaqueous electrolyte may be a nonaqueous electrolytic solution. The nonaqueous electrolytic solution contains a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent.

[0073] 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.

[0074] 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. Among these, EC is preferred.

[0075] 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.

[0076] It is preferable to use a cyclic carbonate or a chain carbonate as the non-aqueous solvent, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and improve the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0077] 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.

[0078] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2, lithium oxalates such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP), and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0079] The content of electrolyte salt in the non-aqueous electrolyte is 0.1 mol / dm at 20°C and 1 atmosphere. 3 More than 2.5mol / dm 3 It is preferable that the value is 0.3 mol / dm or less. 3 More than 2.0mol / dm 3 It is more preferable that it is 0.5 mol / dm or less. 3 More than 1.7mol / dm 3 It is more preferable that it is 0.7 mol / dm or less. 3 More than 1.5mol / dm 3 By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0080] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of 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); aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, and the like. Carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1 ,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. These additives may be used alone or in combination of two or more.

[0081] 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 or cycle performance after high-temperature storage, and further improve reliability.

[0082] The shape of the energy storage element of this embodiment is not particularly limited, and examples thereof include a cylindrical battery, a prismatic battery, a flat battery, a coin battery, and a button battery.

[0083] FIG. 1 shows an energy storage element 1 as an example of a prismatic battery. Note that this figure is a see-through view of the inside of the container. An electrode 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.

[0084] <Configuration of the power storage device> The energy storage element of this embodiment can be mounted as an energy storage unit (battery module) comprising a plurality of energy storage elements 1 in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source. In particular, it can be suitably used as an assist power source for the engine of an HEV or PHEV. In this case, the technology of the present invention may be applied to at least one energy storage element included in the energy storage unit. 2 shows an example of an energy storage device 30 in which energy storage units 20, each of which is an assembly of two or more electrically connected energy storage elements 1, are further assembled. The energy storage device 30 may include a bus bar (not shown) that electrically connects the two or more energy storage elements 1, a bus bar (not shown) that electrically connects the two or more energy storage units 20, etc. The energy storage units 20 or the energy storage device 30 may include a status monitoring device (not shown) that monitors the status of the one or more energy storage elements 1.

[0085] <Method of manufacturing an energy storage element> The method for manufacturing the energy storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode assembly, preparing a non-aqueous electrolyte, and housing the electrode assembly and the non-aqueous electrolyte in a container. Preparing the electrode assembly includes preparing a positive electrode and a negative electrode, and forming the electrode assembly by stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween.

[0086] 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.

[0087] <Other embodiments> The energy storage device of the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0088] In the above embodiment, the case where the energy storage element is used as a chargeable and dischargeable non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) has been described, but the energy storage element may be of any type, shape, size, capacity, etc. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors. [Example]

[0089] 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.

[0090] [Example 1] (Preparation of positive electrode) N-methyl-2-pyrrolidone (NMP) was used as the dispersion medium, LiFePO4 as the positive electrode active material, acetylene black as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder. A positive electrode mixture paste was prepared by mixing the positive electrode active material, conductive agent, and binder in a solid mass ratio of 91:5:4. Next, the positive electrode mixture paste was applied to both sides of an aluminum foil positive electrode substrate, leaving uncoated areas (areas where the positive electrode active material layer was not formed), and then dried and roll-pressed to form a positive electrode active material layer on the positive electrode substrate. The amount of the positive electrode mixture paste applied was 11 mg / cm2 in solids. 2 The LiFePO4 powder had an average particle size of 3 μm and a specific surface area of ​​15 m 2 / g was used.

[0091] (Preparation of negative electrode) A negative electrode mixture paste was prepared by mixing water as the dispersion medium, graphite as the negative electrode active material, styrene butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the thickener in a solids mass ratio of 96:3:1. This negative electrode mixture paste was applied to both sides of copper foil, the negative electrode substrate, leaving uncoated areas (areas where the negative electrode active material layer was not formed), and then dried to prepare a negative electrode active material layer. A negative electrode was then fabricated by roll pressing. Graphite with an average particle size of 3 μm was used.

[0092] (Preparation of non-aqueous electrolyte) A mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 30:35:35 was added with LiPF6 at a concentration of 1.1 mol / dm 3A non-aqueous electrolyte was prepared by dissolving the solution at a concentration of 100 ppm.

[0093] (separator) The separator used was an inorganic particle-containing polyethylene resin film made of a microporous resin film made of polyethylene, containing aluminum oxide as inorganic particles, and having an air permeability per unit thickness shown in Table 1. The air permeability per unit thickness of the separator was 4 sec / (100 cm 3 The average thickness was 15 μm and the porosity was 58%.

[0094] (Fabrication of energy storage element) Next, the positive electrode and the negative electrode were stacked with the separator interposed therebetween and wound to prepare an electrode assembly. This electrode assembly was housed in an aluminum prismatic container, and a positive electrode terminal and a negative electrode terminal were attached. The nonaqueous electrolyte was poured into the prismatic container, which was then sealed to obtain the energy storage element of Example 1.

[0095] [Example 2] An electricity storage element of Example 2 was produced in the same manner as in Example 1, except that LiFePO4 with an average particle size of 7 μm was used.

[0096] [Comparative Example 1] An energy storage element of Comparative Example 1 was produced in the same manner as in Example 1, except that instead of the inorganic particle-containing polyethylene resin film, an inorganic particle-layer-laminated polyethylene resin film was used as the separator, the inorganic particle layer-laminated polyethylene resin film having an air permeability per unit thickness shown in Table 1 and including a base layer made of a microporous resin film made of polyethylene and an inorganic particle layer laminated on one side of the base layer. The inorganic particle layer contained aluminosilicate as inorganic particles and a binder.

[0097] Comparative Example 2 Instead of LiFePO4, Li[Ni 0.33 Mn 0.33 Co 0.33 An electricity storage element of Comparative Example 2 was produced in the same manner as in Example 1, except that ]O2 was used as the positive electrode active material.

[0098] Comparative Example 3 Instead of LiFePO4, Li[Ni 0.33 Mn 0.33 Co 0.33 An electricity storage element of Comparative Example 3 was produced in the same manner as in Comparative Example 1, except that ]O2 was used as the positive electrode active material.

[0099] Comparative Example 4 An electricity storage element of Comparative Example 4 was produced in the same manner as in Example 1, except that the positive electrode active material, the conductive agent, and the binder were mixed in a solid content mass ratio of 88:8:4.

[0100] [evaluation] (Output performance test at SOC 50%) The output performance at an SOC of 50% was evaluated according to the following procedure, where SOC is a value that represents the state of charge of the storage element when a fully charged state is taken as 100%. The energy storage devices of Example 1, Example 2, Comparative Example 1, and Comparative Example 4 were charged at a constant current of 1 C to a maximum charge voltage of 3.5 V in a 25°C environment, followed by constant voltage charging at 3.5 V for 60 minutes. After a 10-minute rest period, they were discharged at a constant current of 1 C to a minimum discharge voltage of 2.0 V in a 25°C environment, and the "1 C discharge capacity in a 25°C environment" was measured. Next, half of this "1 C discharge capacity in a 25°C environment" was set as SOC50%, and the device was charged from a discharged state in a 25°C environment at a charge current of 1 C until the SOC reached 50%. The device was then discharged for 10 seconds in a 25°C environment at a discharge current of 15 C, followed by a 10-minute rest period, followed by supplementary charging for 10 seconds at a charge current of 15 C. Similarly, the discharge current and supplementary charging were adjusted to 30C and 45C, and the output [W] was calculated from the battery voltage 10 seconds after the start of discharge at each discharge current. For the storage elements of Comparative Example 2 and Comparative Example 3, the output [W] was calculated using the same procedures as in Example 1, Example 2, Comparative Example 1, and Comparative Example 4, except that the upper limit charging voltage was changed to 4.2 V and the lower limit discharging voltage was changed to 2.5 V. The results of the output performance tests are shown in Tables 1 and 2. Here, the test results for Example 1, Example 2, Comparative Example 1, and Comparative Example 4 are shown as relative values ​​when the output of Comparative Example 1 is set to 100%. Furthermore, the test results for Comparative Examples 2 and 3 are shown as relative values ​​when the output of Comparative Example 3 is set to 100%.

[0101] (internal short circuit test) An internal short circuit test (nail penetration test) was carried out on Example 1, Example 2, and Comparative Examples 1 to 4 in the following manner. The energy storage elements of Example 1, Example 2, Comparative Example 1, and Comparative Example 4 were charged at a constant current of 1 C to an upper charge voltage of 3.5 V in a 25°C environment, and then charged at a constant voltage of 3.5 V for 2 hours. After charging, the positive and negative electrodes were short-circuited by piercing the energy storage elements with a stainless steel nail in a 70°C environment. The temperature of the container of the energy storage elements during the internal short-circuit test was measured using a thermocouple. The energy storage elements of Comparative Example 2 and Comparative Example 3 were subjected to an internal short-circuit test using the same procedure as in Example 1, Example 2, Comparative Example 1, and Comparative Example 4, except that the upper charge voltage was changed to 4.2 V. Table 1 shows the maximum temperatures reached by the containers of the energy storage elements during the internal short circuit tests in Example 1, Example 2, and Comparative Examples 1 to 4.

[0102] [Table 1]

[0103] [Table 2]

[0104] As shown in Tables 1 and 2, the air permeability per unit thickness of the lithium nickel cobalt manganese composite oxide and the carbon material is 4.0 sec / (100 cm 3 The electric storage element of Comparative Example 2, which uses a combination of an inorganic particle-containing polyethylene resin film having an air permeability of 4.0 sec / (100 cm ) or less and a polyanionic compound and a carbon material, 3In the energy storage element of Comparative Example 4, which used a combination of an inorganic particle-containing polyethylene resin film having a particle size of 0.1 μm or less and a conductive agent content of 8 mass % in the positive electrode active material layer, the maximum temperature of the container of the energy storage element exceeded 90°C during the internal short circuit test. Furthermore, the energy storage element of Comparative Example 1 only achieved an improvement of about 2% in output at SOC 50% compared to the energy storage element of Comparative Example 3. In contrast, the energy storage element of Comparative Example 1, which used a polyanionic compound, a carbon material, and a polyethylene resin film having an air permeability per unit thickness of 4.0 sec / (100 cm 3 In the energy storage devices of Examples 1 and 2, in which a polyanionic compound, a carbon material, and an inorganic particle-containing polyethylene resin film having a particle diameter of 0.1 μm or less were used in combination, and the content of the conductive agent in the positive electrode active material layer was 6 mass % or less, the maximum temperature of the container of the energy storage device during an internal short circuit test was below 90°C, and the energy storage device had good resistance to internal short circuits. Furthermore, the energy storage device of Example 1 had an output at SOC 50% that was improved by 7% or more compared to the energy storage device of Comparative Example 1. These results confirmed that by using a polyanionic compound, a carbon material, and an inorganic particle-containing polyolefin resin film having the above-mentioned specific air permeability per unit thickness in combination, a synergistic effect of the combination can be achieved, resulting in an energy storage device that has excellent output performance and high resistance to internal short circuits.

[0105] The above results demonstrate that the energy storage element has excellent output performance and high resistance to internal short circuits. [Industrial Applicability]

[0106] The present invention is suitably used as an electricity storage element, including a non-aqueous electrolyte secondary battery used as an assist power source for the engine of an automobile such as an HEV or PHEV. [Explanation of symbols]

[0107] 1. Energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy storage unit 30 Energy storage device

Claims

1. a positive electrode containing a positive electrode active material and a conductive agent; a negative electrode containing a negative electrode active material; a separator interposed between the negative electrode and the positive electrode; Equipped with the content of the conductive agent in the positive electrode is 6% by mass or less, the positive electrode active material contains a polyanionic compound, the negative electrode active material contains a carbon material, the separator has a substrate layer made of a porous polyolefin-based resin film, the substrate layer contains inorganic particles, The separator has an air permeability of 4.0 seconds / (100 cm 3 ・An energy storage element having a thickness of 1 μm or less.

2. 2. The energy storage element according to claim 1, wherein the separator has an average thickness of 18 μm or less.

3. 3. The energy storage element according to claim 1, wherein the separator has a porosity of 58% or less.

4. 4. The energy storage device according to claim 1, wherein the polyanionic compound has an average particle size of 5 μm or less.

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