Positive electrode mixture for power storage element, positive electrode for power storage element, power

Abstract

A positive electrode mixture for a power storage element according to one aspect of the present invention contains a positive electrode active material and a conductive auxiliary agent, the conductive auxiliary agent contains carbon nanotubes, and in a Log differential pore volume distribution, the ratio B / A of the maximum value B [cm3 / g] of the differential pore volume in the range of a pore diameter of 100 nm to 3000 nm to the maximum value A [cm3 / g] of the differential pore volume in the range of a pore diameter of 10 nm to 100 nm is 4.50 or more.

Description

Technical Field

[0001] The present invention relates to a positive electrode mixture for an electricity storage element, a positive electrode for an electricity storage element, an electricity storage element, and an electricity storage device. Background Art

[0002] Non-aqueous electrolyte secondary batteries, represented by lithium-ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as in automobiles, due to their high energy density. These non-aqueous electrolyte secondary batteries are generally composed of a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes. Charge and discharge are achieved by transferring ions between the two electrodes. As storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double-layer capacitors, as well as storage elements using electrolytes other than non-aqueous electrolytes, have also become widely used.

[0003] An electric storage device is desired to have excellent output performance. In order to improve the output of an electric storage device, a conductive agent (also called a conductive auxiliary agent) is sometimes added to the positive electrode mixture (see Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2012-209161 Summary of the Invention

[0007] To increase the output of a storage element, it is preferable that the electrolyte of the storage element fully penetrate into the pores of the positive electrode mixture. On the other hand, if large pores are provided between the positive electrode active materials to allow the electrolyte to penetrate into the pores of the positive electrode mixture, the conductive path through the conductive additive may not be properly formed, thereby increasing the resistance of the storage element.

[0008] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a positive electrode mixture for an electric storage element and a positive electrode for an electric storage element capable of reducing the resistance of the electric storage element, as well as an electric storage element and an electric storage device having low resistance.

[0009] A positive electrode mixture for an electric storage device according to one aspect of the present invention comprises a positive electrode active material and a conductive additive, wherein the conductive additive comprises carbon nanotubes, and wherein the maximum value B [cm2] of the differential pore volume in the range of pore diameters of 100 nm to 3000 nm in the Log differential pore volume distribution is 0.0547 W / cm2. 3 / g] and the maximum value A of the differential pore volume in the range of pore diameter 10nm to 100nm [cm 3 / g] and a ratio B / A of 4.50 or more.

[0010] A positive electrode for an energy storage device according to another aspect of the present invention includes the positive electrode mixture for an energy storage device.

[0011] An electric storage device according to still another aspect of the present invention includes the electric storage device positive electrode.

[0012] A power storage device according to still another aspect of the present invention includes two or more power storage elements and one or more of the power storage elements.

[0013] The positive electrode mixture for an electricity storage device according to one aspect of the present invention and the positive electrode for an electricity storage device according to another aspect of the present invention can reduce the resistance of the electricity storage device.

[0014] A power storage element and a power storage device according to still another aspect of the present invention have low resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a transparent perspective view showing one embodiment of an energy storage element including an energy storage element positive electrode.

[0016] Figure 2 This is a schematic diagram of one embodiment of an electricity storage device formed by assembling a plurality of electricity storage elements each including a positive electrode for the electricity storage element. DETAILED DESCRIPTION

[0017] First, an overview of the positive electrode mixture for an electricity storage element, the positive electrode for an electricity storage element, the electricity storage element, and the electricity storage device disclosed in this specification will be described.

[0018] (1) A positive electrode mixture for an electric storage device according to one aspect of the present invention comprises a positive electrode active material and a conductive additive, wherein the conductive additive comprises carbon nanotubes, and wherein the maximum value B [cm2] of the differential pore volume in the range of pore diameters of 100 nm to 3000 nm in the Log differential pore volume distribution is 3 / g] and the maximum value A of the differential pore volume in the range of pore diameter 10nm to 100nm [cm 3 / g] and a ratio B / A of 4.50 or more.

[0019] The positive electrode mixture for storage elements described in (1) above can reduce the resistance of the storage element. The reason for this is not yet determined, but it is speculated to be the following. In this positive electrode mixture, the pore volume of the pores of the positive electrode active material and the pore volume of the pores in the range of 100nm to 3000nm, which means the gaps between the positive electrode active material particles, is larger than the pore volume of the pores in the range of 10nm to 100nm, which means the pores of the conductive auxiliary agent. With such a conventional positive electrode mixture for storage elements, the electrolyte of the storage element easily penetrates between the positive electrode active material particles, but the conductive path between the positive electrode active material particles based on the conductive auxiliary agent cannot be fully formed, and the resistance of the storage element may increase. In contrast, with the positive electrode mixture for storage elements described in (1) above, since the conductive auxiliary agent contains carbon nanotubes, even when the gaps between the positive electrode active material particles are large, the conductive path between the positive electrode active material particles can be easily formed by the conductive auxiliary agent. Furthermore, since the ratio of the pore volume of the conductive additive to the pore volume of the positive electrode active material and between the positive electrode active material particles is appropriately controlled, the conductive additive is appropriately dispersed in the positive electrode mixture for the energy storage device and is easily disposed between the positive electrode active material particles. Therefore, the positive electrode mixture for the energy storage device described in (1) can reduce the resistance of the energy storage device.

[0020] (2) In the positive electrode mixture for an electric storage device described in (1) above, the content of the conductive auxiliary agent may be 0.1% by mass to 3.0% by mass.

[0021] The positive electrode mixture for storage elements described in (2) above can both reduce the resistance of the storage element and achieve a high capacity of the storage element. The reason is presumably as follows. Generally, by reducing the content of the conductive auxiliary agent in the positive electrode mixture for storage elements and relatively increasing the content of the positive electrode active material, a high capacity of the storage element can be achieved. However, if the content of the conductive auxiliary agent in the positive electrode mixture for storage elements is reduced, the conductive auxiliary agent cannot fully form a conductive path between the positive electrode active material particles, and the resistance of the storage element is likely to increase. In this regard, as described above, the positive electrode mixture for storage elements described in (2) above is constructed in a manner that allows the conductive path based on the conductive auxiliary agent to be appropriately formed, so it is easy to reduce the resistance even when the content of the conductive auxiliary agent in the positive electrode mixture for storage elements is small. Therefore, by setting the content of the conductive auxiliary agent in the positive electrode mixture for storage elements described in (2) above to the above range, it is possible to both reduce the resistance of the storage element and achieve a high capacity of the storage element.

[0022] (3) A positive electrode for an electric storage device according to another aspect of the present invention includes the positive electrode mixture for an electric storage device according to (1) or (2).

[0023] Since the positive electrode for an energy storage device described in (3) above includes the positive electrode mixture for an energy storage device described in (1) or (2) above, the resistance of the energy storage device can be reduced.

[0024] (4) An electric storage device according to another aspect of the present invention includes the positive electrode mixture for an electric storage device according to (1) or (2) above, or the positive electrode for an electric storage device according to (3) above.

[0025] The energy storage device described in (4) above includes the positive electrode mixture for an energy storage device described in (1) or (2) above or the positive electrode for an energy storage device described in (3) above, and therefore has low resistance.

[0026] In the present invention, the "Log differential pore volume" of the positive electrode mixture for an energy storage device is measured by the mercury intrusion method according to the following procedure.

[0027] The pore volume distribution of the positive electrode mixture for storage elements was measured by mercury intrusion using AutoPore9400 (Micromeritics). The contact angle of mercury was set to 130° and the surface tension was set to 484 dynes / cm. The pore diameter range for measurement was set to be from 10 nm to 12000 nm. The pore diameter was plotted as the horizontal axis and the pore volume as the vertical axis to obtain the cumulative pore volume curve. Next, the value obtained by dividing the differential volume dV between the measurement points by the difference value d (logD) of the logarithm of the pore diameter was obtained, and the curve was plotted relative to the average pore diameter of each interval to obtain the Log differential pore volume curve. The "maximum value of the differential pore volume in the pore diameter range of 10 nm to 100 nm" is set as the maximum value of the Log differential pore volume in the pore diameter range of 10 nm to 100 nm in the above-mentioned Log differential pore volume curve, and the "maximum value of the differential pore volume in the pore diameter range of 100 nm to 3000 nm" is set as the maximum value of the Log differential pore volume in the pore diameter range of 100 nm to 3000 nm in the above-mentioned Log differential pore volume curve.

[0028] In the present invention, the "content (content percentage) of the conductive auxiliary agent" in the positive electrode mixture for an energy storage device is determined by the following procedure based on thermogravimetric differential thermal analysis (TG-DTA).

[0029] First, the mass W0 [mg] of a sample of approximately 10 mg of the positive electrode mixture for storage elements is measured at room temperature with an accuracy of 0.01 mg. Next, using a thermogravimetric differential thermal analyzer, the sample is heated from 30°C to 900°C at a heating rate of 2°C / min in an air atmosphere. At this time, the mass W1 [mg] of the sample at 460°C and the mass W2 [mg] at 700°C are measured with an accuracy of 0.01 mg. The content P of the conductive additive in the positive electrode mixture for storage elements m[Mass %] was calculated by the following formula.

[0030] P m ={(W1-W2) / W0}×100

[0031] It should be noted that the sample of the positive electrode mixture used for the above-mentioned measurement of the pore volume distribution and the above-mentioned thermogravimetric differential thermal analysis is prepared according to the following steps when constituting the positive electrode of the storage element assembled with the positive electrode mixture. The storage element is discharged at a current of 0.1C to the discharge termination voltage during normal use, and is put into a discharged state. Here, "normal use" refers to the case where the storage element is used under the discharge conditions recommended or specified for the storage element. The storage element in the discharged state is disassembled, the positive electrode is taken out as the working electrode, and metal Li is used as the counter electrode to assemble a half-cell, and discharged at a current of 0.1C until the positive electrode potential is 3.0V (vs. Li / Li + ). Disassemble the half-cell, thoroughly wash the removed positive electrode with dimethyl carbonate, and dry it under reduced pressure at room temperature. Cut out a positive electrode mixture of a specified size (for example, 2 cm × 2 cm) from the dried positive electrode as a sample for the above-mentioned measurement of the pore volume distribution. In addition, collect more than 10 mg of the positive electrode mixture from the dried positive electrode as a sample for the above-mentioned thermogravimetric differential thermal analysis. The operations from disassembly of the storage element to cutting out or collecting the measurement sample are carried out in a dry air atmosphere with a dew point below -40°C.

[0032] (5) A power storage device according to another aspect of the present invention includes two or more power storage elements and includes one or more power storage elements described in (4) above.

[0033] Since the power storage device described in (5) above includes one or more power storage elements described in (4) above, the resistance is small.

[0034] The following describes in detail a positive electrode mixture for an energy storage element, a positive electrode for an energy storage element, an energy storage element, an energy storage device, a method for manufacturing an energy storage element, and other embodiments of the present invention. It should be noted that the names of the components (constituent elements) used in each embodiment may differ from the names of the components (constituent elements) used in the background art.

[0035] [Positive electrode mixture for energy storage devices]

[0036] In one embodiment of the present invention, a positive electrode mixture for a storage element (hereinafter referred to as a "positive electrode mixture") comprises a positive electrode active material and a conductive additive. The positive electrode mixture may also contain optional components such as a binder, a thickener, and a filler, as needed. For example, the positive electrode mixture may be a positive electrode active material layer laminated on a positive electrode substrate of a storage element.

[0037] (Positive electrode active material)

[0038] As the positive electrode active material, it can be appropriately selected from the known positive electrode active materials. As the positive electrode active material for lithium ion secondary batteries, materials that can absorb and release lithium ions are generally used. As the positive electrode active material, for example, lithium transition metal composite oxides having an α-NaFeO2 type crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanion compounds, chalcogen compounds, sulfur, etc. can be cited. As the lithium transition metal composite oxide having an α-NaFeO2 type crystal structure, for example, 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, 0<1-x-γ), 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, 0<1-x-γ), 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, 0<1-x-γ-β), 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, 0<1-x-γ-β) etc. As lithium transition metal composite oxides having a spinel crystal structure, Li x Mn2O4、Li x Ni γ Mn (2 - γ)O4, etc. Examples of polyanionic compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, and Li2CoPO4F. Examples of chalcogenides include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. The atoms or polyanions in these materials may be partially replaced by atoms or anionic substances composed of other elements. The surfaces of these materials may also be covered with other materials. In the positive electrode mixture, one of these materials may be used alone, or two or more may be mixed.

[0039] As the positive electrode active material, from the viewpoint of increasing energy density, lithium transition metal composite oxides are preferred, lithium transition metal composite oxides having an α-NaFeO2 type crystal structure are more preferred, and 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, 0<1-x-γ-β), the lithium transition metal composite oxide represented by the chemical formula is further preferred, and the lithium transition metal composite oxide represented by the chemical formula of 0.55<γ is further preferred, and the lithium transition metal composite oxide represented by 0.75<γ is particularly preferred.

[0040] The positive electrode active material is generally a particle (powder). As the lower limit of the average particle size of the positive electrode active material, it is preferably 0.1 μm, more preferably 1 μm, and further preferably 3 μm. On the other hand, as the upper limit of the average particle size of the positive electrode active material, it is preferably 20 μm, more preferably 16 μm, and further preferably 12 μm. By making the average particle size of the positive electrode active material above the above lower limit, it is easy to manufacture or handle the positive electrode active material. By making the average particle size of the positive electrode active material below the above upper limit, the electronic conductivity of the positive electrode mixture is improved. In addition, the average particle size of the positive electrode active material can be above any of the above lower limits and below any of the above upper limits. It should be noted that when a composite of the positive electrode active material and other materials 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 particle size distribution measured using the laser diffraction / scattering method based on a solution of particles diluted in a solvent in accordance with JIS-Z-8825 (2013), and the 50% value (D50) of the volume standard cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001). The average particle size based on this measurement has been confirmed to be substantially consistent with the average particle size measured by extracting 100 positive electrode active material particles from a scanning electron microscope (SEM) image of the positive electrode mixture, avoiding both very large and very small positive electrode active material particles. It should be noted that the particle size of each positive electrode active material particle measured in this SEM image is the Feret diameter, and the volume of each positive electrode active material particle is calculated based on a sphere with the Feret diameter as its diameter.

[0041] In order to obtain the positive electrode active material with a specified particle size, a pulverizer, a classifier, etc. can be used. As a pulverization method, for example, a method using a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter-current mill (Counter Jet Mill), a rotary airflow jet mill or a sieve can be mentioned. During pulverization, wet pulverization coexisting with an organic solvent such as water or hexane can also be used. As a classification method, a sieve, an air classifier, etc. can be used. As needed, both dry and wet methods can be used.

[0042] The content of the positive electrode active material in the positive electrode mixture is preferably 95.0% to 99.0% by mass, more preferably 96.0% to 99.0% by mass, and even more preferably 97.0% to 99.0% 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 mixture can be achieved.

[0043] (Conductive additive)

[0044] In one embodiment of the present invention, the conductive additive includes carbon nanotubes (CNTs). Examples of CNTs include single-walled carbon nanotubes (SWCNTs) formed from one layer of graphene, multi-walled carbon nanotubes (MWCNTs) formed from two or more layers of graphene (e.g., 2 to 20 layers, typically 2 to 60 layers), and the like. Alternatively, CNTs may be formed by containing SWCNTs and MWCNTs in any ratio (the mass ratio of SWCNT:MWCNT is, for example, 100:0 to 0:100, preferably 100:0 to 80:20). The structure of CNTs is not particularly limited and may be any of a chiral (helical) type, a zigzag type, and an armchair type. Furthermore, catalyst metals used in the synthesis of CNTs (e.g., Fe, Co, and platinum group elements (Ru, Rh, Pd, Os, Ir, Pt)) may also be included.

[0045] The conductive additive may also include materials other than CNTs. Examples of such materials include carbonaceous materials other than CNTs, metals, conductive ceramics, and the like. Examples of carbonaceous materials other than CNTs include graphite, non-graphite carbon, and graphene-based carbon. Examples of non-graphite 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 and fullerene. Examples of the shapes of these materials include powdered and fibrous forms. Materials other than CNTs may be contained alone or in a mixture of two or more. In addition, CNTs may be used in combination with these materials. For example, a material composed of a composite of CNTs and carbon black may be used. Among materials other than CNTs, carbon black is preferred from the perspective of electronic conductivity and coating properties, and acetylene black is preferred.

[0046] As the lower limit of the content of the conductive auxiliary agent in the positive electrode mixture, it is preferably 0.1 mass %, more preferably 0.3 mass %, and further preferably 0.5 mass %. On the other hand, as the upper limit of the content of the conductive auxiliary agent in the positive electrode mixture, it is preferably 3.0 mass %, more preferably 2.5 mass %, further preferably less than 2.0 mass %, and further preferably 1.5 mass %. By making the content of the conductive auxiliary agent above the above lower limit, the electronic conductivity of the positive electrode mixture is improved. In addition, by making the content of the conductive auxiliary agent below the above upper limit, the energy density of the storage element can be increased. As the content of the conductive auxiliary agent, it can be above any of the above lower limits and below any of the above upper limits.

[0047] As the lower limit of the content of carbon nanotubes (CNTs) in the positive electrode mixture, it is preferably 0.1 mass %, more preferably 0.2 mass %, and further preferably 0.3 mass %. On the other hand, as the upper limit of the content of CNTs in the positive electrode mixture, it is preferably 2.0 mass %, more preferably 1.5 mass %, and further preferably 1.0 mass %. By making the content of CNTs above the above lower limit, the electronic conductivity of the positive electrode mixture is improved. In addition, if the content of CNTs is below the above upper limit, it is easy to appropriately control the later-described Log differential pore volume distribution of the positive electrode mixture. As the content of CNTs, it can be above any of the above lower limits and below any of the above upper limits.

[0048] As adhesives, for example, there can be mentioned thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic acid, polyimide, etc.; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, etc.; polysaccharide polymers, etc.

[0049] The content of the binder in the positive electrode mixture is preferably 1% to 10% by mass, more preferably 1.5% to 9% by mass. When the content of the binder is within the above range, the positive electrode active material can be stably retained.

[0050] As thickeners, for example, polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose can be mentioned. In the case where the thickener has a functional group that reacts with lithium or the like, the functional group can be inactivated in advance by methylation or the like. When a thickener is used, the content of the thickener in the positive electrode mixture can be set to 0.1% by mass to 8% by mass, generally preferably 5% by mass or less, more preferably 2% by mass or less. The technology disclosed herein is preferably implemented in a manner such that the positive electrode mixture does not contain a thickener.

[0051] The filler is not particularly limited. As fillers, there can be mentioned polyolefins such as polypropylene and polyethylene, inorganic oxides such as silica, aluminum oxide, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide and aluminosilicate, hydroxides such as magnesium hydroxide, calcium hydroxide, aluminum hydroxide, carbonates such as calcium carbonate, insoluble ionic crystals such as calcium fluoride, barium fluoride, barium sulfate, nitrides such as aluminum nitride and silicon nitride, talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica and other substances from mineral resources or their artificial products. When a filler is used, the content of the filler in the positive electrode mixture can be set to 0.1% by mass to 8% by mass, usually preferably 5% by mass or less, more preferably 2% by mass or less. The technology disclosed herein is preferably implemented in a manner where the positive electrode mixture does not contain a filler.

[0052] The positive electrode mixture may also contain typical non-metallic elements such as B, N, P, F, Cl, Br, I, typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as ingredients other than the positive electrode active material, conductive additive, binder, thickener, and filler.

[0053] In the Log differential pore volume distribution of the positive electrode mixture, the maximum value B [cm 3 / g] and the maximum value A of the differential pore volume in the range of pore diameter 10nm to 100nm [cm 3 / g] The lower limit of the ratio B / A is 4.50, preferably 5.00, more preferably 5.50, further preferably 6.00, and further preferably 6.50. On the other hand, the upper limit of the above-mentioned ratio B / A is preferably 14.00, more preferably 12.00, further preferably 10.00, and further preferably 8.00. If the above-mentioned ratio B / A is set to be above the above-mentioned lower limit, the electrolyte of the storage element can easily penetrate into the positive electrode active material particles, and the conductive auxiliary agent can easily be evenly dispersed. In addition, if the above-mentioned ratio B / A is set to be below the above-mentioned upper limit, the conductive auxiliary agent can easily form a conductive path between the positive electrode active material particles. The above-mentioned ratio B / A can be above any of the above-mentioned lower limits and below any of the above-mentioned upper limits. It should be noted that the Log differential pore volume distribution of the positive electrode mixture can be controlled by adjusting the content ratio of the conductive auxiliary agent, the mixing method when preparing the positive electrode mixture, the rotation speed and mixing time of the mixer, the pressing pressure when forming the positive electrode mixture on the positive electrode substrate, etc.

[0054] The positive electrode mixture preferably has a peak in differential pore volume (hereinafter referred to as the "first peak") within the pore diameter range of 10 nm to 100 nm in the Log differential pore volume distribution. Furthermore, the first peak in the Log differential pore volume distribution is preferably located within a pore diameter range of 20 nm to 95 nm, more preferably within a pore diameter range of 30 nm to 90 nm, and even more preferably within a pore diameter range of 40 nm to 85 nm. By locating the first peak within this pore diameter range, the resistance of the energy storage device can be further reduced.

[0055] In the Log differential pore volume distribution of the positive electrode mixture, the maximum value A [cm 3 / g], preferably 0.010 cm 3 / g~0.070cm 3 / g, more preferably 0.015cm 3 / g~0.060cm 3 / g, more preferably 0.020cm 3 / g~0.050cm 3 By setting the maximum value A within the above range, the resistance of the energy storage device can be further reduced. In addition, the maximum value A may also be the differential pore volume of the first peak.

[0056] The positive electrode mixture preferably has a peak in differential pore volume (hereinafter also referred to as the "second peak") within the pore diameter range of 100 nm to 3000 nm in the Log differential pore volume distribution. Furthermore, the position of the second peak in the Log differential pore volume distribution is preferably between 200 nm and 2500 nm in pore diameter, more preferably between 300 nm and 2000 nm in pore diameter, and even more preferably between 400 nm and 1500 nm in pore diameter. By locating the second peak within the above pore diameter range, the resistance of the battery cell can be further reduced.

[0057] In the Log differential pore volume distribution of the positive electrode mixture, the maximum value B [cm 3 / g], preferably 0.050cm 3 / g~0.400cm 3 / g, more preferably 0.080cm 3 / g~0.300cm 3 / g, more preferably 0.100cm 3 / g~0.250cm 3 By setting the maximum value B within the above range, the resistance of the energy storage device can be further reduced. In addition, the maximum value B may also be the differential pore volume at the second peak.

[0058] [Positive electrode for energy storage device]

[0059] A positive electrode for an energy storage device according to one embodiment of the present invention comprises a positive electrode substrate and a positive electrode active material layer disposed directly on the positive electrode substrate or via an intermediate layer. The positive electrode active material layer is composed of the positive electrode mixture for an energy storage device. The composition of the positive electrode mixture for an energy storage device has been described above, and therefore, a detailed description thereof will be omitted.

[0060] The positive electrode substrate has electrical conductivity. Whether it has "electrical conductivity" is determined by the volume resistivity 10 measured in accordance with JIS-H-0505 (1975). -2Ω·cm is the threshold value for judgment. As the material of the positive electrode substrate, metals such as aluminum, titanium, tantalum, stainless steel, or their alloys can be used. Among them, from the viewpoints of potential resistance, high conductivity and cost, aluminum or aluminum alloys are preferred. As the positive electrode substrate, foil, vapor-deposited film, mesh, porous material, etc. can be mentioned. From the viewpoint of cost, foil is preferred. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. As aluminum or aluminum alloy, A1085, A3003, A1N30, etc. specified in JIS-H-4000 (2014) or JIS-H-4160 (2006) can be mentioned.

[0061] 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 this range, the strength of the positive electrode substrate can be increased while also increasing the energy density per unit volume of the storage device.

[0062] The intermediate layer is positioned between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive additive, such as carbon particles, to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The structure of the intermediate layer is not particularly limited; for example, it may contain a binder and a conductive additive. This conductive additive may be the same as that used in the positive electrode mixture described above.

[0063] [Electrical storage element]

[0064] The storage element involved in one embodiment of the present invention comprises an electrode body having a positive electrode for the storage element (hereinafter also referred to as a "positive electrode"), a negative electrode and a separator, an electrolyte, and a container for accommodating the above-mentioned electrode body and electrolyte. The electrode body is generally a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked via a separator, or a wound type in which a positive electrode and a negative electrode are stacked via a separator. The electrolyte exists in a state of being impregnated in the positive electrode, the negative electrode and the separator. As an example of a storage element, a non-aqueous electrolyte secondary battery (hereinafter referred to as a "secondary battery") is described. In addition, the structure of the positive electrode for the storage element is as described above, so its description is omitted.

[0065] <Negative electrode>

[0066] The negative electrode comprises a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The structure of the intermediate layer is not particularly limited and can be selected from the structures exemplified for the positive electrode described above.

[0067] The negative electrode substrate has electrical conductivity. As the material of the negative electrode substrate, metals such as copper, nickel, stainless steel, nickel-plated steel, aluminum, or their alloys, carbon materials, etc. can be used. Among them, copper or copper alloys are preferred. As the negative electrode substrate, foil, vapor-deposited film, mesh, porous material, etc. can be mentioned. From the perspective of cost, foil is preferred. Therefore, as the negative electrode substrate, copper foil or copper alloy foil is preferred. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0068] 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 this range, the strength of the negative electrode substrate can be increased while also increasing the energy density per unit volume of the storage element.

[0069] The negative electrode active material layer contains a negative electrode active material. Optionally, the negative electrode active material layer may contain any components such as a conductive additive, a binder, a thickener, and a filler. These components may be selected from the materials exemplified above for the positive electrode.

[0070] The negative electrode active material layer may also contain typical non-metallic elements such as B, N, P, F, Cl, Br, I, typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, 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 additive, binder, thickener, and filler.

[0071] The negative electrode active material can be appropriately selected from known negative electrode active materials. Generally, materials that can absorb and release lithium ions can be used as negative electrode active materials for lithium ion secondary batteries. Examples of negative electrode active materials include metal Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; Li4Ti5O 12 Titanium-containing oxides such as LiTiO2, TiNb2O7, and others; polyphosphate compounds; silicon carbide; carbon materials such as graphite and non-graphitic carbon (easily graphitizable carbon or non-graphitizable carbon). Of these materials, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, any one of these materials may be used alone, or a mixture of two or more may be used.

[0072] “Graphite” refers to the average lattice spacing (d) of the (002) plane determined by X-ray diffraction before charge or discharge or in the discharged state. 002) is a carbon material having a diameter of 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. From the perspective of obtaining a material with stable physical properties, artificial graphite is preferred.

[0073] “Non-graphite carbon” refers to the average lattice spacing (d) of the (002) plane determined by X-ray diffraction before charge and discharge or in the discharged state. 002 ) is a carbon material having a diameter of 0.34 nm to 0.42 nm. Examples of non-graphite carbon include hard-graphite carbon and easy-graphite carbon. Examples of non-graphite carbon include resin-derived materials, petroleum pitch or materials derived from petroleum pitch, petroleum coke or materials derived from petroleum coke, plant-derived materials, and alcohol-derived materials.

[0074] Here, the "discharge state" of a carbonaceous material refers to a state in which lithium ions, which can be stored and released, are fully released from the carbonaceous material, which serves as the negative electrode active material, during charge and discharge. For example, in a half-cell comprising a negative electrode containing a carbonaceous material as the negative electrode active material as the working electrode and metallic lithium as the counter electrode, the open circuit voltage is 0.7 V or higher.

[0075] “Non-graphitizable carbon” refers to the above-mentioned 002 It is a carbon material with a diameter of 0.36nm to 0.42nm.

[0076] “Graphitizable carbon” refers to the above-mentioned 002 A carbon material having a diameter of 0.34 nm or more and less than 0.36 nm.

[0077] The negative electrode active material is generally in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm to 100 μm. When the negative electrode active material is a carbon material, a titanium oxide or a polyphosphate compound, its average particle size can also be 1 μm to 100 μm. When the negative electrode active material is Si, Sn, Si oxide or Sn oxide, etc., its average particle size can also be 1 nm to 1 μm. By setting the average particle size of the negative electrode active material to be above the above lower limit, it is easy to manufacture or handle the negative electrode active material. By setting the average particle size of the negative electrode active material to be below the above upper limit, the electronic conductivity of the negative electrode active material layer is improved. In order to obtain powder of a specified particle size, a pulverizer, a classifier, etc. can be used. The pulverization method and the classification method can be selected from the methods exemplified in the above-mentioned positive electrode. When the negative electrode active material is a metal such as metal Li, the negative electrode active material layer can also be in the form of a foil.

[0078] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% to 99% by mass, more preferably 90% to 98% by mass. By setting the content of the negative electrode active material to the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer. When the negative electrode active material is metallic Li, the content of the negative electrode active material in the negative electrode active material layer may be 99% by mass or more, or 100% by mass.

[0079] <Isolators>

[0080] The separator can be appropriately selected from known separators. As the separator, for example, a separator consisting only of a substrate layer, a separator in which a heat-resistant layer containing heat-resistant particles and an adhesive is formed on one or both surfaces of the substrate layer, etc. can be used. As the shape of the substrate layer of the separator, woven fabrics, non-woven fabrics, and porous resin films can be cited. Among these shapes, from the viewpoint of strength, porous resin films are preferred, and from the viewpoint of liquid retention of non-aqueous electrolytes, non-woven fabrics are preferred. As the material of the substrate layer of the separator, from the viewpoint of the cutting function, for example, polyolefins such as polyethylene and polypropylene are preferred, and from the viewpoint of resistance to oxidative decomposition, polyimides, aromatic polyamides, etc. are preferred. As the substrate layer of the separator, a material composited with these resins can also be used.

[0081] 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. Materials that exhibit a mass loss below the specified value 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; covalent crystals such as silicon and diamond; and mineral-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. Inorganic compounds may be used alone or as a composite, or as a mixture of two or more. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of safety of the energy storage device.

[0082] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value and is measured using a mercury porosimeter.

[0083] As a separator, a polymer gel composed of a polymer and an electrolyte can be used. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinyl pyrrolidone, and polyvinylidene fluoride. Using a polymer gel can effectively suppress liquid leakage. As a separator, a porous resin film or nonwoven fabric as described above can be used in combination with a polymer gel.

[0084] <Non-aqueous electrolyte>

[0085] As the non-aqueous electrolyte, a non-aqueous electrolyte solution may be used. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0086] As the non-aqueous solvent, it is possible to suitably select from known non-aqueous solvents. The non-aqueous solvent includes cyclic carbonates, chain carbonates, carboxylates, phosphoric acid esters, sulfonic acid esters, ethers, amides, nitrile, etc. As the non-aqueous solvent, it is possible to use a solvent in which a part of the hydrogen atoms contained in these compounds is substituted with a halogen atom.

[0087] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, fluorinated ethylene carbonate (FEC), difluorinated ethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. Among them, EC is preferred.

[0088] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. Among them, EMC is preferred.

[0089] As the non-aqueous solvent, preferably a cyclic carbonate or a chain carbonate is used, and more preferably a cyclic carbonate and a chain carbonate are used in combination. By using a cyclic carbonate, the dissociation of the electrolyte salt can be promoted, and the ion conductivity of the non-aqueous electrolyte can be improved. By using a chain carbonate, the viscosity of the non-aqueous electrolyte can be controlled to be low. 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 5:95 to 50:50, for example.

[0090] As the electrolyte salt, it can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, Among them, lithium salts are preferred.

[0091] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2; lithium oxalates such as lithium di(oxalato)borate (LiBOB), lithium difluorooxalatoborate (LiFOB), and lithium difluorobis(oxalato)phosphate (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.

[0092] The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / dm at 20°C and 1 atmosphere. 3 ~2.5mol / dm 3 , more preferably 0.3 mol / dm 3 ~2.0mol / dm 3 , more preferably 0.5 mol / dm 3 ~1.7mol / dm 3 , particularly preferably 0.7 mol / dm 3 ~1.5mol / dm 3 By setting the content of the electrolyte salt to be within the above range, the ion conductivity of the non-aqueous electrolyte solution can be improved.

[0093] In addition to the non-aqueous solvent and the electrolyte salt, the non-aqueous electrolyte may also contain additives. Examples of additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); lithium oxalates such as lithium bis(oxalato)borate (LiBOB), lithium difluorooxalatoborate (LiFOB), and lithium difluorobis(oxalato)phosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI); biphenyl, alkylbiphenyl, terphenyl, partial hydride of terphenyl, cyclohexylbenzene, Aromatic compounds such as tert-butylbenzene, tert-amylbenzene, diphenyl ether, dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole; vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, succinic anhydride, glutaric anhydride, Maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; vinyl sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, vinyl sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiapentane), 4-Methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridyl disulfide, 1,3-propylene 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.

[0094] The content of the additive in the non-aqueous electrolyte is preferably 0.01% to 10% by mass relative to the mass of the entire non-aqueous electrolyte, more preferably 0.1% to 7% by mass, further preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass. By making the content of the additive within the above range, the capacity retention performance or charge-discharge cycle performance after high-temperature storage can be improved, thereby further improving safety.

[0095] A solid electrolyte may be used as the non-aqueous electrolyte, or a non-aqueous electrolyte solution and a solid electrolyte may be used in combination.

[0096] The solid electrolyte can be selected from any material that has ion conductivity and is solid at room temperature (e.g., 15° C. to 25° C.), such as lithium, sodium, and calcium. Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and polymer solid electrolytes.

[0097] As sulfide solid electrolytes, in the case of lithium ion secondary batteries, for example, Li2S-P2S5, LiI-Li2S-P2S5, Li 10 Ge-P2S 12 wait.

[0098] The shape of the electric storage element of the present embodiment is not particularly limited, and examples thereof include cylindrical batteries, rectangular batteries, flat batteries, coin batteries, and button batteries.

[0099] Figure 1 This figure shows an energy storage element 1, which is an example of a rectangular battery. Note that this figure shows the interior of the container. An electrode assembly 2, comprising a positive electrode and a negative electrode wound with a separator interposed therebetween, is housed in a rectangular container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0100] [Electricity Storage Device]

[0101] The energy storage element of this embodiment can be installed as an energy storage unit (battery module) composed of a plurality of energy storage elements, such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), as a power supply for vehicles such as personal computers and communication terminals, or as a power supply for power storage. In this case, the technology of the present invention can be applied to at least one energy storage element included in the energy storage unit.

[0102] An energy storage device according to one embodiment of the present invention includes two or more energy storage elements, including one or more energy storage elements according to the above-described embodiment of the present invention (hereinafter referred to as the "second embodiment"). The at least one energy storage element included in the energy storage device of the second embodiment may be a single energy storage element according to the above-described embodiment of the present invention, one or more energy storage elements other than the above-described embodiment of the present invention, or two or more energy storage elements according to the above-described embodiment of the present invention, as long as the technology of the above-described embodiment of the present invention is applied.

[0103] Figure 2shows an example of an electrical storage device 30 according to the second embodiment, which is formed by further assembling electrical storage units 20, each comprising two or more electrically connected electrical storage elements 1. The electrical storage device 30 may also include a busbar (not shown) electrically connecting the two or more electrical storage elements 1, a busbar (not shown) electrically connecting the two or more electrical storage units 20, and the like. The electrical storage units 20 or the electrical storage device 30 may further include a status monitoring device (not shown) that monitors the status of one or more electrical storage elements.

[0104] [Method for Manufacturing Electricity Storage Element]

[0105] The method for manufacturing the energy storage element of this embodiment can be appropriately selected from known methods. This method includes, for example, the following steps: 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 the following steps: preparing a positive electrode and a negative electrode, and then stacking or winding the positive and negative electrodes with a separator to form the electrode assembly.

[0106] The method for storing 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 can be injected from an injection port formed on the container and then sealed.

[0107] [Other embodiments]

[0108] It should be noted that the positive electrode mixture for an energy storage element, the positive electrode for an energy storage element, and the energy storage element of the present invention are not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the present invention. For example, the configuration of one embodiment may be supplemented with the configuration of another embodiment, or a portion of the configuration of one embodiment may be replaced with the configuration of another embodiment or with known technology. Furthermore, a portion of the configuration of one embodiment may be deleted. Furthermore, known technology may be added to the configuration of one embodiment.

[0109] In the above embodiment, the case where the positive electrode mixture for an electric storage element and the positive electrode for an electric storage element are used in a rechargeable non-aqueous electrolyte secondary battery (e.g., a lithium-ion secondary battery) is described. However, the type, shape, size, capacity, etc. of the electric storage element in which the positive electrode mixture for an electric storage element and the positive electrode for an electric storage element are used are arbitrary. The present invention is also applicable to various secondary batteries, capacitors such as electric double-layer capacitors and lithium-ion capacitors, and electric storage elements using electrolytes other than non-aqueous electrolytes.

[0110] Example

[0111] Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following Examples.

[0112] [Example 1]

[0113] (Production of positive electrode)

[0114] As the positive electrode active material, prepare LiNi 0.8 Mn 0.1 Co 0.1 The lithium transition metal composite oxide (NCM811) represented by O2 had an average particle size (D50) of 12 μm as measured by the above method.

[0115] Using N-methylpyrrolidone (NMP) as a dispersion medium, the above-mentioned positive electrode active material, carbon nanotubes (CNTs) as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder are mixed in a mass ratio of 97.9:0.6:1.5 in terms of solid content to prepare a mixture. It should be noted that the above-mentioned carbon nanotubes use multi-walled carbon nanotubes (MWCNTs). The above-mentioned mixture is kneaded using a high-speed mixer (manufactured by PRIMIX Co., Ltd., "Filmix" (registered trademark)) to obtain a positive electrode mixture slurry. The positive electrode mixture slurry is applied to both sides of an aluminum foil serving as a positive electrode substrate. It is then dried and rolled to obtain a positive electrode active material layer consisting of the positive electrode mixture of Example 1. In addition, the positive electrode of Example 1 on which the above-mentioned positive electrode active material layer is formed is obtained.

[0116] (Fabrication of negative electrode)

[0117] A negative electrode mixture slurry was prepared by mixing graphite (Gr) as the negative electrode active material, styrene-butadiene rubber (SBR) as the binder, carboxymethyl cellulose (CMC) as the thickener, and water as the dispersion medium. The mass ratio of Gr, SBR, and CMC, calculated on a solids basis, was 96:2:2. This negative electrode mixture slurry was applied to both sides of a copper foil serving as the negative electrode substrate, dried, and roll-pressed to form a negative electrode active material layer, thus producing a negative electrode.

[0118] (Preparation of non-aqueous electrolyte)

[0119] In a solvent composed of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:35:35, LiPF6 as an electrolyte salt was added at a concentration of 1.2 mol / dm 3 The concentration of 2-hydroxy-2-nitropropene is dissolved to obtain a non-aqueous electrolyte.

[0120] (Production of Energy Storage Elements)

[0121] The positive electrode and negative electrode are stacked via a separator made of a polyolefin microporous film to produce an electrode assembly. This electrode assembly is housed in a container made of a metal-resin composite film, the nonaqueous electrolyte is injected into the container, and the container is sealed by heat welding to produce a storage element.

[0122] [Comparative Example 1]

[0123] The mass ratio of the positive electrode active material, carbon black (CB) as a conductive aid and the binder in the above mixture is set to 94.5:4.0:1.5 in terms of solid content. The rotation speed and mixing time of the high-speed mixer are changed. Except for this, the same steps as in Example 1 are followed to obtain a positive electrode and a storage element having a positive electrode active material layer formed by the positive electrode mixture of Comparative Example 1.

[0124] It should be noted that in the present embodiment and the comparative example, the total content of the positive electrode active material and the conductive additive in the positive electrode mixture and the positive electrode active material layer was adjusted to 98.5% by mass, and the content of the binder was 1.5% by mass, which did not change. In addition, in the present embodiment and the comparative example, acetylene black (AB) was used as the carbon black.

[0125] [Example 2, Comparative Example 2 and Comparative Example 3]

[0126] The average particle size (D50) of the positive electrode active material and the type and content of the conductive additive are set as shown in Table 1. The speed and mixing time of the high-speed mixer are changed. In addition, the same steps as in Example 1 are followed to obtain a positive electrode and a storage element having a positive electrode active material layer composed of the positive electrode mixtures of Example 2, Comparative Example 2 and Comparative Example 3.

[0127] [Comparative Examples 4 to 6]

[0128] As the positive electrode active material, prepare LiNi 0.6 Mn 0.2 Co 0.2 O2 represents a lithium transition metal composite oxide (NCM622). The average particle size (D50) of the positive electrode active material measured by the above method was 12 μm. In addition, the type and content of the conductive additive were set as shown in Table 2, the speed and mixing time of the high-speed mixer were changed, and the pressing pressure when the positive electrode mixture was rolled was changed. Otherwise, the same procedures as in Example 1 were followed to obtain positive electrodes and storage elements having positive electrode active material layers formed from the positive electrode mixtures of Comparative Examples 4 to Comparative Examples 6.

[0129] The Log differential pore volume distribution of the positive electrode mixture was determined for each of the obtained energy storage devices by the above method. The pore diameter (first peak position) [nm] and the differential pore volume (first peak height, maximum value A) [cm] at which the differential pore volume is maximum in the pore diameter range of 10 nm to 100 nm in the Log differential pore volume distribution were calculated. 3 / g], and the pore diameter (second peak position) [nm] where the differential pore volume is the largest in the pore diameter range of 100 nm to 3000 nm, and its differential pore volume (second peak height, maximum value B) [cm3 / g] are shown in Tables 1 and 2. In addition, the ratio of the maximum value B to the maximum value A (peak height ratio, B / A) is shown in Tables 1 and 2.

[0130] [evaluate]

[0131] (Initial charge and discharge)

[0132] Each energy storage element produced using each positive electrode was initially charged and discharged under the following conditions.

[0133] In a thermostatic chamber at 25°C, constant current charging was performed at a charging current of 1.0C and a charge end voltage of 4.20V, followed by constant voltage charging at 4.20V. The charging was terminated when the charging current reached 0.01C. A rest period of 10 minutes was then set. Constant current discharge was then performed at a current of 0.2C and a discharge end voltage of 2.50V. This charge and discharge cycle was repeated twice. Based on the second discharge, the initial discharge capacity per unit mass of the storage element [mAh / g] was measured.

[0134] (DC resistance test)

[0135] The direct current resistance (DCR) of each energy storage element after the initial charge and discharge was evaluated by the following procedure.

[0136] In a thermostatic chamber at 25°C, a constant current charge of 10% of the initial discharge capacity was performed at a charging current of 1C. After the SOC (State of Charge) of each storage element was set to 10%, each storage element was kept in a thermostatic chamber at 25°C for 4 hours. Then, the elements were discharged at currents of 0.1C, 0.2C, and 0.3C for 30 seconds. A curve was drawn with the voltage 10 seconds after the start of each discharge as the vertical axis and the discharge current as the horizontal axis, and the value corresponding to the gradient, that is, the DC resistance [mΩ], was calculated from the obtained current-voltage characteristic diagram as the 25°C DCR. The DC resistance (DCR) of each storage element is shown in Tables 1 and 2. The DC resistance (DCR) in Table 1 is a relative value based on the DCR of the storage element obtained from Comparative Example 1 for Example 1 and Comparative Example 1, and a relative value based on the DCR of the storage element obtained from Comparative Example 3 for Example 2 and Comparative Example 3. Note that, in Comparative Example 2, DCR was too large to be measured, so DCR is indicated by "-" in Table 1. The DC resistance (DCR) in Table 2 is a relative value based on the DCR of the storage element obtained in Comparative Example 4.

[0137] [Table 1]

[0138] [Table 2]

[0139] As shown in Table 1, the energy storage device of Example 1, in which the conductive additive contained CNTs and had a peak height ratio of 4.50 or greater, exhibited lower resistance than the energy storage device of Comparative Example 1, in which the conductive additive contained no CNTs and had a peak height ratio of less than 4.50. Furthermore, the energy storage device of Example 2, in which the conductive additive contained CNTs and had a peak height ratio of 4.50 or greater, exhibited lower resistance than the energy storage device of Comparative Example 3, which contained no conductive additive and had a peak height ratio of less than 4.50. Furthermore, the energy storage device of Comparative Example 2, in which the conductive additive contained no CNTs and had a peak height ratio of 4.50 or greater, exhibited significantly higher resistance.

[0140] As shown in Table 2, the energy storage element of Comparative Example 6, in which the conductive additive contained CNTs and the peak height ratio was less than 4.50, had a higher resistance than the energy storage elements of Comparative Examples 4 and 5, in which the conductive additive did not contain CNTs and the peak height ratio was less than 4.50.

[0141] From the above, it is considered that the resistance is reduced by satisfying both the conductive agent containing CNTs and the peak height ratio being 4.50 or greater. However, it is difficult to reduce the resistance by controlling only the composition of the conductive agent or the peak height ratio.

[0142] In Examples 1 and 2, the content of the conductive additive in the positive electrode mixture is 1.5% by mass or less. This reduces the resistance while allowing the content of the conductive additive to be reduced, thereby increasing the capacity of the energy storage device.

[0143] Industrial applicability

[0144] The present invention is applicable to power storage devices used as power sources for electronic devices such as personal computers and communication terminals, and automobiles.

[0145] Explanation of symbols

[0146] 1 Storage element

[0147] 2 Electrode body

[0148] 3 Containers

[0149] 4 Positive terminal

[0150] 41 positive wire

[0151] 5 Negative terminal

[0152] 51 negative wire

[0153] 20 power storage units

[0154] 30 Power storage device

Claims

1. A positive electrode mixture for a storage element, comprising a positive electrode active material and a conductive additive, The conductive additive comprises carbon nanotubes, In the Log differential pore volume distribution, the ratio B / A of the maximum differential pore volume B in the pore diameter range of 100 nm to 3000 nm to the maximum differential pore volume A in the pore diameter range of 10 nm to 100 nm is 4.50 or more, wherein The unit of A and B is cm 3 / g.

2. The positive electrode mixture for an electric storage device according to claim 1, wherein The content of the conductive auxiliary agent is 0.1% by mass to 3.0% by mass. 3 . A positive electrode for an energy storage device, comprising the positive electrode mixture for an energy storage device according to claim 1 . 4 . An electric storage device comprising the positive electrode for an electric storage device according to claim 3 . 5 . A power storage device comprising two or more power storage elements, and comprising one or more power storage elements according to claim 4 .

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