Positive electrode for non-aqueous electrolyte power storage element, and non-aqueous

Abstract

A positive electrode for a non-aqueous electrolyte electricity storage element according to one aspect of the present invention has a positive electrode active material layer containing: first positive electrode active material particles having a Feret diameter of 5 [mu] m or less in a projected image observed by a scanning electron microscope (SEM); second positive electrode active material particles having a Feret diameter greater than 5 [mu] m in a projected image observed by SEM; and a conductive agent. The content of the conductive agent in the positive electrode active material layer is less than 1.1 mass%, and the first positive electrode active material particles are secondary particles having a ratio of an average secondary particle diameter to an average primary particle diameter of 3 or less or are substantially non-agglomerated primary particles.

Description

Technical Field

[0001] The present invention relates to a positive electrode for a nonaqueous electrolyte power storage device and a nonaqueous electrolyte power storage device having the positive electrode. Background Art

[0002] Non-aqueous electrolyte secondary batteries represented by lithium-ion secondary batteries are mostly used in electronic devices such as personal computers, communication terminals, and automobiles due to their high energy density. Non-aqueous electrolyte secondary batteries generally have a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte between the electrodes, and are configured to charge and discharge by receiving and receiving charge transfer ions between the two electrodes. In addition, as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and double-layer capacitors have also been widely popularized.

[0003] A positive electrode used in a non-aqueous electrolyte storage device generally has a positive electrode active material layer formed of a positive electrode mixture containing a positive electrode active material, a conductive agent, a binder, and the like (see Patent Documents 1 and 2).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2014 / 156116

[0007] Patent Document 2: International Publication No. 2010 / 106768 Summary of the invention

[0008] In order to improve the energy density of the non-aqueous electrolyte storage element, for example, it is possible to reduce the content of the conductive agent in the positive electrode active material layer and increase the content of the positive electrode active material. However, when the content of the conductive agent is reduced, the capacity retention rate of the non-aqueous electrolyte storage element after the charge and discharge cycle is sometimes greatly reduced.

[0009] An object of the present invention is to provide a positive electrode for a non-aqueous electrolyte storage element and a non-aqueous electrolyte storage element having such a positive electrode, wherein the positive electrode for the non-aqueous electrolyte storage element can suppress the decrease in the capacity retention rate of the non-aqueous electrolyte storage element after charge and discharge cycles that occurs when the content of the conductive agent in the positive electrode active material layer is reduced.

[0010] A positive electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention has a positive electrode active material layer, which includes: a first positive electrode active material particle having a Feret diameter of less than 5 μm according to a projection image observed by a scanning electron microscope (SEM), a second positive electrode active material particle having a Feret diameter of greater than 5 μm according to a projection image observed by the SEM, and a conductive agent; the content of the conductive agent in the positive electrode active material layer is less than 1.1% by mass, and the first positive electrode active material particles are secondary particles having a ratio of an average secondary particle size to an average primary particle size of less than 3 or are substantially unagglomerated primary particles.

[0011] A nonaqueous electrolyte electricity storage device according to one aspect of the present invention includes a positive electrode for a nonaqueous electrolyte electricity storage device according to one aspect of the present invention.

[0012] According to one aspect of the present invention, there can be provided a positive electrode for a non-aqueous electrolyte storage element and a non-aqueous electrolyte storage element having such a positive electrode, wherein the positive electrode for the non-aqueous electrolyte storage element can suppress a decrease in the capacity retention rate of the non-aqueous electrolyte storage element after charge and discharge cycles that occurs when the content of the conductive agent in the positive electrode active material layer is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a perspective view showing one embodiment of a non-aqueous electrolyte electricity storage element.

[0014] Figure 2 This is a schematic diagram showing one embodiment of an electricity storage device constituted by assembling a plurality of nonaqueous electrolyte electricity storage elements. DETAILED DESCRIPTION

[0015] First, the outlines of the positive electrode for the nonaqueous electrolyte electricity storage device and the nonaqueous electrolyte electricity storage device disclosed in this specification are described.

[0016] [1]: A positive electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention comprises a positive electrode active material layer, wherein the positive electrode active material layer comprises: a first positive electrode active material particle having a Feret diameter of less than 5 μm according to a projection image observed by a scanning electron microscope (SEM), a second positive electrode active material particle having a Feret diameter of greater than 5 μm according to a projection image observed by the SEM, and a conductive agent; the conductive agent content of the positive electrode active material layer is less than 1.1% by weight, and the first positive electrode active material particles are secondary particles having a ratio of an average secondary particle size to an average primary particle size of less than 3 or are substantially non-agglomerated primary particles.

[0017] According to the positive electrode described in [1] above, it is possible to suppress the reduction in the capacity retention rate of the non-aqueous electrolyte storage element after the charge and discharge cycle that occurs when the content of the conductive agent in the positive electrode active material layer is reduced. The reason is unclear, but it is speculated to be the following reason. The inventors found that when the content of the conductive agent in the positive electrode active material layer is less than 1.1% by mass, particle breakage starting from the grain boundary of the positive electrode active material particles composed of secondary particles with a small particle size and micronization caused by the particle breakage occur at the beginning of the charge and discharge cycle, thereby causing a reduction in the capacity retention rate. In contrast, secondary particles having an average secondary particle size of less than 3 relative to the average primary particle size or substantially unagglomerated primary particles (hereinafter, these particles are also referred to as "single particle system particles") have fewer grain boundaries than general secondary particles formed by agglomeration of multiple primary particles, so it is difficult to produce particle breakage starting from the grain boundary and micronization caused by the particle breakage at the beginning of the charge and discharge cycle. In the positive electrode described in [1] above, the first positive electrode active material particles having a small particle size (Ferret diameter) of less than 5 μm are such single-particle particles, which can suppress the pulverization of the positive electrode active material particles, thereby suppressing the reduction in the capacity retention rate of the non-aqueous electrolyte storage element after charge and discharge cycles.

[0018] The Feret diameter of the positive electrode active material particles (the first positive electrode active material particles and the second positive electrode active material particles) contained in the positive electrode active material layer and the average primary particle size and the average secondary particle size of the first positive electrode active material particles are measured values ​​of the projection images of 50 randomly selected positive electrode active material particles observed in the SEM image obtained by using the SEM of the positive electrode active material particles. Specifically, they are obtained as follows.

[0019] (1) Preparation of test samples

[0020] The positive electrode to be measured is fixed with a thermosetting resin. For the positive electrode fixed with the resin, the cross section is exposed by using a cross-section polisher to prepare a sample for measurement. It should be noted that the positive electrode to be measured is prepared by the following steps. The non-aqueous electrolyte storage element is discharged at a constant current of 0.1C to the discharge end voltage during normal use, as a discharged state. It should be noted that normal use refers to the case where the non-aqueous electrolyte storage element is used under the recommended or specified charging and discharging conditions of the non-aqueous electrolyte storage element. The non-aqueous electrolyte storage element in the discharged state is disassembled, the positive electrode is taken out, and after being fully cleaned with dimethyl carbonate, it is dried under reduced pressure at room temperature. The operation from disassembly of the non-aqueous electrolyte storage element to preparation of the positive electrode to be measured is carried out in a dry air atmosphere with a dew point below -40°C. It should be noted that in the case where the positive electrode before assembling the non-aqueous electrolyte storage element can be prepared, the positive electrode before assembly can be used as the measurement object.

[0021] (2) Acquisition of SEM images

[0022] In obtaining the SEM image, a JSM-7001F (manufactured by JEOL Ltd.) was used as a scanning electron microscope. The SEM was used to observe secondary electron images. The accelerating voltage was set to 15 kV. The observation magnification was set to a magnification at which the number of positive electrode active material particles appearing in one field of view was between 3 and 15. The obtained SEM image was saved as an image file. In addition, the conditions such as the spot diameter, working distance, irradiation current, brightness, and focus were appropriately set in a manner that made the outline of the positive electrode active material particles clear and distinct.

[0023] (3) Calculation of Feret diameter of positive electrode active material particles

[0024] 50 positive electrode active material particles are randomly selected from the obtained SEM image, and the Feret diameter (oriented diameter) of the projection image (area surrounded by the outer contour line) of each positive electrode active material particle is measured. Particles with a measured Feret diameter of 5 μm or less are the first positive electrode active material particles, and particles with a measured Feret diameter greater than 5 μm are the second positive electrode active material particles. That is, each positive electrode active material particle is classified as one of the first positive electrode active material particle and the second positive electrode active material particle based on whether the Feret diameter is 5 μm or less.

[0025] (4) Calculation of the average primary particle size and average secondary particle size of the first positive electrode active material particles

[0026] For each positive electrode active material particle classified as the first positive electrode active material particle in (3) above, the Feret diameter (primary particle size) of the primary particles constituting each first positive electrode active material particle is determined. The primary particle refers to a particle in which no grain boundary is observed in appearance in the above SEM image. The average value of the measured primary particle diameters (Feret diameters of primary particles) is taken as the average primary particle diameter.

[0027] It should be noted that the average value of the Feret diameters of the first positive electrode active material particles obtained in (3) above is taken as the average secondary particle size of the first positive electrode active material particles. When the first positive electrode active material particles include positive electrode active material particles consisting only of primary particles, the average secondary particle size is calculated by also including the Feret diameter of the positive electrode active material particles.

[0028] It should be noted that the average primary particle size and the average secondary particle size of the second positive electrode active material particles can also be determined by the same procedure as that of the first positive electrode active material particles.

[0029] The “substantially non-aggregated primary particles” refer to primary particles in which a plurality of primary particles are not aggregated but exist independently, or primary particles in a state in which primary particles are substantially not directly bonded to other primary particles in the above-mentioned SEM image.

[0030] [2]: In the positive electrode described in [1], the conductive agent may be fibrous carbon. By using fibrous carbon as the conductive agent, good conductivity can be ensured regardless of the amount of the conductive agent, thereby improving the discharge capacity and energy density of the non-aqueous electrolyte storage element.

[0031] "Fibrous carbon" refers to a deformable, elongated carbonaceous material. The ratio of the average length of the fibrous carbon to the average diameter is 10 or more. The average diameter and average length of the fibrous carbon are measured values ​​of any 10 fibrous carbons in the SEM image obtained by the same method as the Feret diameter of the positive electrode active material particles.

[0032] [3]: In the positive electrode described in [1] or [2] above, the average primary particle size of the first positive electrode active material particles may be greater than 2.8 μm. In this case, the large average primary particle size of the first positive electrode active material particles means that each first positive electrode active material particle is composed of a smaller number of primary particles. In this case, the first positive electrode active material particles are less likely to be micronized, thereby further suppressing the reduction in the capacity retention rate of the non-aqueous electrolyte storage element after charge and discharge cycles.

[0033] [4]: In the positive electrode described in any one of [1] to [3] above, the first positive electrode active material particle may include a transition metal composite oxide containing a nickel element. In this case, it is possible to effectively suppress a decrease in the capacity retention rate of the non-aqueous electrolyte storage element after charge and discharge cycles, which is particularly likely to occur when the content of the conductive agent in the positive electrode active material layer is reduced.

[0034] [5]: A nonaqueous electrolyte storage device according to one aspect of the present invention comprises the positive electrode according to any one of [1] to [4]. The nonaqueous electrolyte storage device according to [5] suppresses the decrease in capacity retention after charge and discharge cycles that occurs when the content of the conductive agent in the positive electrode active material layer is reduced.

[0035] A positive electrode for a non-aqueous electrolyte storage element according to an embodiment of the present invention, a method for manufacturing the same, a non-aqueous electrolyte storage element, a storage device, a method for manufacturing a non-aqueous electrolyte storage element, and other embodiments are described in detail. It should be noted that the names of the components (components) used in each embodiment are sometimes different from the names of the components (components) used in the background art.

[0036] <Positive electrode for non-aqueous electrolyte storage device>

[0037] A positive electrode for a nonaqueous electrolyte storage device according to one embodiment of the present invention (hereinafter also simply referred to as “positive electrode”) includes a positive electrode substrate and a positive electrode active material layer provided directly on the positive electrode substrate or via an intermediate layer.

[0038] 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). 7 Ω·cm is used as 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 these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity and cost. As the positive electrode substrate, foil, vapor-deposited film, mesh, porous material, etc. can be cited. 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-H4160 (2006) can be exemplified.

[0039] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, further preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By making the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be improved, and the energy density per unit volume of the non-aqueous electrolyte storage element can be improved.

[0040] The intermediate layer is a layer provided between the positive electrode substrate and the positive electrode active material layer. The intermediate layer reduces the contact resistance between the positive electrode substrate and the positive electrode active material layer by including a conductive agent such as carbon particles. The composition of the intermediate layer is not particularly limited, and for example, includes a binder and a conductive agent.

[0041] The positive electrode active material layer includes a first positive electrode active material particle with a Feret diameter of 5 μm or less, a second positive electrode active material particle with a Feret diameter of more than 5 μm, and a conductive agent. The content of the conductive agent in the positive electrode active material layer is less than 1.1% by mass, and the first positive electrode active material particle is a secondary particle with a ratio of an average secondary particle size to an average primary particle size of less than 3 or a substantially non-agglomerated primary particle. In this way, by combining the first positive electrode active material particle with a small particle size of less than 5 μm and the second positive electrode active material particle with a Feret diameter of more than 5 μm, the filling rate of the positive electrode active material particles (the first positive electrode active material particle and the second positive electrode active material particle) in the positive electrode active material layer is increased, thereby improving the energy density of the obtained non-aqueous electrolyte storage element. In addition, the content of the conductive agent in the positive electrode active material layer is less than 1.1% by mass, and the amount is small, so the content of the positive electrode active material in the positive electrode active material layer corresponding to the amount thereof can be increased, thereby further improving the energy density of the non-aqueous electrolyte storage element. Moreover, when the content of the conductive agent in the positive electrode active material layer is less than 1.1 mass %, although the particle fracture starting from the grain boundary of the positive electrode active material particles composed of secondary particles with a small particle size and the micronization caused by the particle fracture occur at the initial stage of the charge and discharge cycle, thereby causing a decrease in the capacity retention rate, according to the above-mentioned structure, the second positive electrode active material particles with a large particle size and a Feret diameter greater than 5 μm are secondary particles with multiple grain boundaries. In this case, even if the particle fracture starting from the grain boundary occurs at the initial stage of the charge and discharge cycle, the particle size after the particle fracture remains relatively large, and micronization is difficult to occur, so the impact on the capacity retention rate of the non-aqueous electrolyte storage element is small. On the other hand, the first positive electrode active material particles with a small particle size and a Feret diameter of 5 μm or less are single-particle particles with fewer grain boundaries than general secondary particles, so the micronization of the positive electrode active material particles is suppressed, thereby suppressing the reduction in the capacity retention rate of the non-aqueous electrolyte storage element after the charge and discharge cycle. Therefore, according to this configuration, the filling rate of the positive electrode active material particles of the positive electrode active material layer is increased and the content of the conductive agent in the positive electrode active material layer is reduced, while the micronization of the positive electrode active material particles can be suppressed, and a high-performance non-aqueous electrolyte storage element that takes into account both high energy density and durability for charge and discharge cycles at a high level can be realized. The positive electrode active material layer may contain any component such as a binder, a thickener, and a filler as required.

[0042] The first positive electrode active material particle is a positive electrode active material particle having a Feret diameter of 5 μm or less. The first positive electrode active material particle is a single-particle particle, that is, a secondary particle having a ratio of an average secondary particle size to an average primary particle size of 3 or less or a substantially non-agglomerated primary particle. The first positive electrode active material particle, which is a so-called small particle, is a single-particle particle that is difficult to be micronized, and thus can suppress a decrease in the capacity retention rate of the non-aqueous electrolyte storage element after charge and discharge cycles that is easily caused when the content of the conductive agent in the positive electrode active material layer is reduced.

[0043] The ratio of the average secondary particle size of the first positive electrode active material particles to the average primary particle size may be less than 2.5, less than 2.0, or less than 1.8 (for example, less than 1.6). In this case, each of the first positive electrode active material particles is composed of a smaller number of primary particles, so the micronization of the first positive electrode active material particles becomes more difficult to produce. The ratio of the average secondary particle size of the first positive electrode active material particles to the average primary particle size may be greater than 1, and may be greater than 1.2. In the case where the first positive electrode active material particles are composed only of substantially unagglomerated primary particles, the ratio of the average secondary particle size of the first positive electrode active material particles to the average primary particle size is 1. The ratio of the average secondary particle size of the first positive electrode active material particles to the average primary particle size may be greater than any of the above lower limits and less than any of the above upper limits.

[0044] As the lower limit of the average primary particle size of the first positive electrode active material particles, for example, it can be 2.0 μm, but preferably 2.5 μm (for example, 2.8 μm). When the average primary particle size of the first positive electrode active material particles is above the above lower limit, the micronization of the first positive electrode active material particles becomes more difficult to occur, thereby further suppressing the reduction in the capacity retention rate of the non-aqueous electrolyte storage element after the charge and discharge cycle. As the upper limit of the average primary particle size of the first positive electrode active material particles, for example, it can be 4.0 μm, or it can be 3.5 μm (for example, 3.0 μm). The average primary particle size of the first positive electrode active material particles can be above any of the above lower limits and below any of the above upper limits.

[0045] The average secondary particle size of the first positive electrode active material particles is, for example, preferably 1.0 μm to 5.0 μm, and more preferably 2.0 μm to 4.8 μm. In several forms, the average secondary particle size of the first positive electrode active material particles may be greater than 3.0 μm, or greater than 3.5 μm. In addition, the average secondary particle size of the first positive electrode active material particles may be less than 4.6 μm, or less than 4.4 μm. The average secondary particle size of the first positive electrode active material particles may be greater than any of the above lower limits and less than any of the above upper limits. By making the average secondary particle size of the first positive electrode active material particles within the above range, the filling rate of the positive electrode active material particles (the first positive electrode active material particles and the second positive electrode active material particles) of the positive electrode active material layer is increased, and the energy density of the obtained non-aqueous electrolyte storage element can be increased.

[0046] The first positive electrode active material particles belonging to the single particle system particles can be manufactured by a known method. The average primary particle size and the like can be controlled by the manufacturing conditions. For example, in the manufacturing process of the positive electrode active material, if the firing temperature is set to a high temperature or the firing time is extended, the crystals of the primary particles will grow and the average primary particle size will increase. Alternatively, the secondary particles can be crushed as primary particles. The first positive electrode active material particles can use commercially available products.

[0047] The second positive electrode active material particles are positive electrode active material particles having a Feret diameter greater than 5 μm. The second positive electrode active material particles may be substantially non-agglomerated primary particles, but are preferably secondary particles from the perspective of manufacturability. The second positive electrode active material particles are relatively large particles, so even if the secondary particles with many grain boundaries cause particle breakage starting from the grain boundaries at the beginning of the charge and discharge cycle, the particle size after the particle breakage remains large, and it is difficult to produce micronization, so the effect on the capacity retention rate is small. The ratio of the average secondary particle size of the second positive electrode active material particles to the average primary particle size can be 2 to 100, or 3 to 20. In several forms, the ratio of the average secondary particle size of the second positive electrode active material particles to the average primary particle size can be 5 or more, or 8 or more (for example, 10 or more). In several forms, the ratio of the average secondary particle size of the second positive electrode active material particles to the average primary particle size can be 18 or less, or 16 or less (for example, 14 or less). The ratio of the average secondary particle size to the average primary particle size of the second positive electrode active material particles may be greater than or equal to the above-described lower limit and less than or equal to the above-described upper limit.

[0048] The lower limit of the average primary particle size of the second positive electrode active material particles may be, for example, 0.2 μm, preferably 0.5 μm (for example, 0.8 μm). The upper limit of the average primary particle size of the second positive electrode active material particles may be, for example, 3.0 μm, or 2.5 μm (for example, 2.0 μm). The average primary particle size of the second positive electrode active material particles may be above any of the lower limits and below any of the upper limits. In a preferred form, the average primary particle size of the second positive electrode active material particles is smaller than the average primary particle size of the first positive electrode active material particles. The ratio of the average primary particle size of the second positive electrode active material particles to the average primary particle size of the first positive electrode active material particles (second positive electrode active material particles / first positive electrode active material particles) is preferably greater than 0.1 and less than 1, and more preferably 0.2 to 0.6 (for example, 0.25 to 0.5). The ratio of the average primary particle size of the second positive electrode active material particles to the average primary particle size of the first positive electrode active material particles (second positive electrode active material particles / first positive electrode active material particles) may be greater than or equal to the above-described lower limit and less than or equal to the above-described upper limit.

[0049] As the average secondary particle size of the second positive electrode active material particles, from the perspective of manufacturability, operability, etc., it is preferably 6.0μm to 20.0μm, and more preferably 8.0μm to 15.0μm. In several forms, the average secondary particle size of the second positive electrode active material particles can be greater than 10.0μm, or greater than 10.5μm. In several forms, the average secondary particle size of the second positive electrode active material particles can be less than 14.0μm, or less than 13.0μm. The average secondary particle size of the second positive electrode active material particles is greater than any lower limit described above and less than any upper limit described above.

[0050] The ratio of the average secondary particle size of the second positive electrode active material particles to the average secondary particle size of the first positive electrode active material particles (second positive electrode active material particles / first positive electrode active material particles) is preferably 1.5 to 10, and more preferably 2 to 6 (for example, 2.5 to 5). The ratio of the average secondary particle size of the second positive electrode active material particles to the average secondary particle size of the first positive electrode active material particles (second positive electrode active material particles / first positive electrode active material particles) can be above any of the lower limits and below any of the upper limits. In addition, the mass ratio of the first positive electrode active material particles and the second positive electrode active material particles contained in the positive electrode active material layer (first positive electrode active material particles: second positive electrode active material particles) is preferably in the range of 1:9 to 9:1, and more preferably in the range of 1.5:8.5 to 7:3. In some forms, the mass ratio of the first positive electrode active material particles to the second positive electrode active material particles (first positive electrode active material particles: second positive electrode active material particles) can be in the range of 1.8:8.2 to 5:5, or in the range of 2:8 to 4:6 (e.g., in the range of 2:8 to 3:7, e.g., 2:8). By making the ratio of the average secondary particle diameters and the mass ratio of the first positive electrode active material particles to the second positive electrode active material particles in the above range, the filling rate of the positive electrode active material particles (first positive electrode active material particles and second positive electrode active material particles) of the positive electrode active material layer is increased, thereby increasing the energy density of the obtained non-aqueous electrolyte storage element.

[0051] In order to obtain the first positive electrode active material particles and the second positive electrode active material particles of 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 reverse jet mill, a rotating airflow jet mill or a sieve can be cited. During pulverization, wet pulverization in which organic solvents such as water or hexane coexist can also be used. As a classification method, a sieve, a wind classifier, etc. can be used in a dry method or a wet method as needed.

[0052] The positive electrode active material constituting the first positive electrode active material particles and the second positive electrode active material particles can be appropriately selected from known positive electrode active materials. As the positive electrode active material for lithium ion secondary batteries, materials that can embed and de-embed lithium ions are generally used. As the positive electrode active material, for example, transition metal composite oxides having an α-NaFeO2 type crystal structure, transition metal composite oxides having a spinel type crystal structure, polyanion compounds, oxygen group element compounds, sulfur, etc. can be cited. As transition metal composite oxides having an α-NaFeO2 type crystal structure, lithium transition metal composite oxides having an α-NaFeO2 type crystal structure, etc. can be cited. As transition metal composite oxides having a spinel type crystal structure, lithium transition metal composite oxides having a spinel type crystal structure, etc. can be cited. As lithium transition metal composite oxides 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. As polyanion compounds, LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. can be mentioned. As oxygen group element compounds, titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. can be mentioned. A part of the atoms or polyanions in these materials can be replaced by atoms or ionic species composed of other elements. The surfaces of these materials can be covered with other materials. One of these materials can be used alone, or two or more can be mixed and used. The first positive electrode active material particles and the second positive electrode active material particles refer to particles that can be composed of the same positive electrode active material or different positive electrode active materials, but are preferably composed of the same positive electrode active material.

[0053] As the positive electrode active material constituting the first positive electrode active material particle and the second positive electrode active material particle, among these, a transition metal composite oxide is also preferred, a transition metal composite oxide containing a nickel element is more preferred, a lithium transition metal composite oxide containing a nickel element is further preferred, and a lithium transition metal composite oxide containing a nickel element, a cobalt element, a manganese element or an aluminum element is further preferred, and a lithium transition metal composite oxide containing a nickel element, a cobalt element, and a manganese element is particularly preferred. The lithium transition metal composite oxide is preferably a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure. By using such a lithium transition metal composite oxide, the energy density can be improved. In addition, these positive electrode active materials are generally manufactured and used in the form of secondary particles formed by the aggregation of a plurality of primary particles. When the content of the conductive agent in the positive electrode active material layer is reduced, micronization occurs through charge and discharge cycles, which easily leads to a phenomenon of reduced capacity retention rate. Therefore, in one embodiment of the present invention, by using these positive electrode active materials for the positive electrode active material particles, especially the first positive electrode active material particles, and the positive electrode active materials have advantages such as high energy density, it is possible to effectively suppress the reduction in the capacity retention rate of the non-aqueous electrolyte storage element after charge and discharge cycles, which is particularly likely to be caused when the content of the conductive agent in the positive electrode active material layer is reduced.

[0054] As the lithium transition metal composite oxide having an α-NaFeO 2 type crystal structure, a compound represented by the following formula (1) is preferred.

[0055] Li 1+α Me 1-α O2…(1)

[0056] In formula (1), Me is a metal element including Ni (excluding Li).

[0057] Me in formula (1) preferably contains Co and Mn or Al in addition to Ni. Me is more preferably substantially composed of three elements of Ni, Co and Mn or three elements of Ni, Co and Al, and further preferably composed of three elements of Ni, Co and Mn. Me may contain other metal elements.

[0058] From the viewpoint of increasing the electric capacity, etc., the preferred content (composition ratio) of each constituent element in the compound represented by formula (1) is as follows: The molar ratio is equivalent to the atomic ratio.

[0059] In formula (1), the lower limit of the molar ratio (Ni / Me) of Ni to Me is preferably 0.3, and sometimes more preferably 0.5 or 0.7. On the other hand, the upper limit of the molar ratio (Ni / Me) is preferably 0.9, and more preferably 0.8. By using these positive electrode active materials for the first positive electrode active material particles, and the positive electrode active materials have advantages such as high energy density, it is possible to effectively suppress the reduction in the capacity retention rate of the non-aqueous electrolyte storage element after the charge and discharge cycle, which is particularly easy to cause when reducing the content of the conductive agent in the positive electrode active material layer.

[0060] In formula (1), the lower limit of the molar ratio (Co / Me) of Co to Me is preferably 0.01, and more preferably 0.05. On the other hand, the upper limit of the molar ratio (Co / Me) is preferably 0.5, and more preferably 0.4 or 0.2.

[0061] In formula (1), the lower limit of the molar ratio of Mn to Me (Mn / Me) is preferably 0.01, and more preferably 0.05. On the other hand, the upper limit of the molar ratio (Co / Me) is preferably 0.5, and more preferably 0.4 or 0.2.

[0062] In formula (1), the lower limit of the molar ratio of Al to Me (Al / Me) may be 0, preferably 0.01, more preferably 0.02 or 0.03. On the other hand, the upper limit of the molar ratio (Al / Me) is preferably 0.3, more preferably 0.2 or 0.1.

[0063] In formula (1), the molar ratio of Li to Me (Li / Me), that is, (1+α) / (1-α), may be 1. On the other hand, the upper limit of the molar ratio (Li / Me) is preferably 1.6, and more preferably 1.4 or 1.2.

[0064] It should be noted that the composition ratio of the lithium transition metal composite oxide is the composition ratio when it is in a fully discharged state by the following method. First, the non-aqueous electrolyte storage element is charged with a constant current at a current of 0.05C with the charging termination voltage during normal use as the end point to make it fully charged. After resting for 30 minutes, constant current discharge is performed at a current of 0.05C with the lower limit voltage during normal use as the end point. After disassembly, the positive electrode is taken out, and a test battery with a metal lithium electrode as the counter electrode is assembled, and a constant current discharge is performed with a current value of 10mA per 1g of positive electrode active material until the positive electrode potential becomes 2.0Vvs.Li / Li + , adjust the positive electrode to a fully discharged state. Disassemble again and take out the positive electrode. Use dimethyl carbonate to thoroughly clean the non-aqueous electrolyte attached to the taken out positive electrode. After drying at room temperature for a day and a night, take the lithium transition metal composite oxide of the positive electrode active material. The taken lithium transition metal composite oxide is provided for measurement. The operations from disassembly of the non-aqueous electrolyte storage element to taking out the lithium transition metal composite oxide are carried out in an argon environment atmosphere with a dew point below -60°C.

[0065] Preferred lithium transition metal composite oxides include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 3 / 5Co 1 / 5 Mn 1 / 5 O2, LiNi 1 / 2 Co 1 / 5 Mn 3 / 10 O2, LiNi 1 / 2 Co 3 / 10 Mn 1 / 5 O2, LiNi 8 / 10 Co 1 / 10 Mn 1 / 10 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, etc.

[0066] The positive electrode active material preferably contains lithium transition metal composite oxide in a ratio of 50 mass % or more (preferably 70 to 100 mass %, more preferably 80 to 100 mass %) in the total positive electrode active material of the positive electrode active material layer. In fact, it is more preferable to use a positive electrode active material consisting only of lithium transition metal composite oxide.

[0067] The content of the positive electrode active material particles (the total of the first positive electrode active material particles and the second positive electrode active material particles) of the positive electrode active material layer is preferably 80% to 99% by mass, and more preferably 85% to 98.5% by mass. The lower limit of the content of the positive electrode active material particles of the positive electrode active material layer is sometimes more preferably 90% by mass, 93% by mass, 95% by mass, 96% by mass, 97% by mass, 98% by mass or 98.0% by mass. By making the content of the positive electrode active material particles of the positive electrode active material layer within the above range, the conductivity and energy density of the positive electrode active material layer can be improved in a balanced manner.

[0068] The conductive agent is not particularly limited if it is a material having conductivity. As such a conductive agent, for example, carbonaceous materials, metals, conductive ceramics, etc. can be cited. As carbonaceous materials, graphite, carbon black (acetylene black, etc.), fibrous carbon, etc. can be cited. As the conductive agent, one of these materials can be used alone, or two or more can be mixed and used. As the conductive agent, from the point of being able to exert conductivity well even in a small amount, among these, a carbonaceous material is preferred, and fibrous carbon is more preferred.

[0069] Examples of fibrous carbon include carbon nanofibers, pitch-based carbon fibers, carbon nanotubes (CNTs), etc. Among these, CNTs, which are graphene-based carbons, can be preferably used.

[0070] As the average diameter of the fibrous carbon, for example, it is preferably 1nm to 300nm, more preferably 3nm to 100nm, further preferably 5nm to 50nm, and further preferably 8nm to 30nm. In several forms, the average diameter of the fibrous carbon can be 9nm or more, and can also be 10nm or more. In several forms, the average diameter of the fibrous carbon can be 20nm or less, and can also be 15nm or less. The average diameter of the fibrous carbon can be above any lower limit mentioned above and below any upper limit mentioned above. By making the average diameter of the fibrous carbon within the above range, even if the content of the conductive agent is small, the conductivity of the positive electrode active material layer can be better, and the discharge capacity, energy density, etc. of the non-aqueous electrolyte storage element can be improved. The "average diameter" of the fibrous carbon refers to the average value of the diameters of any 10 fibrous carbons in the SEM image.

[0071] The average aspect ratio (ratio of average length to average diameter) of the fibrous carbon is, for example, preferably 10 to 10,000, more preferably 100 or more, and further preferably 1,000 or more. In several forms, the average aspect ratio of the fibrous carbon may be 1,500 or more, or 2,000 or more. In several forms, the average aspect ratio of the fibrous carbon may be 6,000 or less, or 3,000 or less. The average aspect ratio of the fibrous carbon may be above any lower limit and below any upper limit. By using fibrous carbon having an average aspect ratio in the above range, better conductivity of the positive electrode active material layer can be achieved, and the discharge capacity and energy density of the non-aqueous electrolyte storage element can be improved. It should be noted that the "average length" of the fibrous carbon refers to the average value of the lengths of any 10 fibrous carbons in the SEM image. When calculating the average aspect ratio, it is preferred that the 10 fibrous carbons used to determine the average diameter and the 10 fibrous carbons used to determine the average length are the same fibrous carbons, but the average diameter and the average length may be determined for 10 different fibrous carbons, respectively, and the ratio thereof may be used as the average aspect ratio. That is, the average aspect ratio refers to the average value of the aspect ratios (length to diameter) of any 10 fibrous carbons in the SEM image, or may be the ratio of the average lengths of any 10 identical or different fibrous carbons to the average diameter of any 10 fibrous carbons in the SEM image.

[0072] The average lattice spacing (d 002 ), preferably less than 0.340 nm. Thus, the average lattice plane spacing (d 002 ) is small and the degree of crystallization is high, the conductivity of the positive electrode active material layer is further improved. It should be noted that the average lattice plane spacing (d 002 ), for example, can be set to 0.330 nm. In addition, the half-value width of the peak corresponding to the (002) plane of the fibrous carbon by the X-ray diffraction method based on the CuKα line is, for example, 0.5° or more. The half-value width of the peak corresponding to the (002) plane of the fibrous carbon is preferably less than 0.7°.

[0073] For example, fibrous carbon can be obtained by spinning a polymer into fibers and heat-treating it in an inert atmosphere, or by vapor growth method in which an organic compound reacts in the presence of a catalyst at a high temperature. As the fibrous carbon, fibrous carbon obtained by vapor growth method (vapor growth method fibrous carbon) is preferred. Fibrous carbon can be obtained by commercial products.

[0074] The content of the conductive agent in the positive electrode active material layer is less than 1.1% by mass, preferably less than 1.0% by mass, and sometimes more preferably less than 0.8% by mass or less than 0.6% by mass. By making the content of the conductive agent in the positive electrode active material layer less than the above upper limit, the content of the positive electrode active material particles can be increased, and as a result, the energy density of the non-aqueous electrolyte storage element can be improved. The lower limit of the content of the conductive agent in the positive electrode active material layer is preferably 0.1% by mass, more preferably 0.3% by mass, and further preferably 0.4% by mass. By making the content of the conductive agent in the positive electrode active material layer more than the above lower limit, sufficient conductivity can be ensured in the positive electrode active material layer. The content of the conductive agent in the positive electrode active material layer can be made to be above the above arbitrary lower limit and less than the above arbitrary upper limit or less than the above arbitrary upper limit.

[0075] As adhesives, for example, there can be mentioned thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylate, polyimide, etc.; elastomers such as ethylene propylene diene monomer rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, etc.; polysaccharide polymers, etc.

[0076] The content of the binder of the positive electrode active material layer is preferably 0.3% to 10% by mass, more preferably 0.5% to 8% by mass, and sometimes more preferably 5% by mass or less, 4% by mass or less, 3% by mass or less, or 2% by mass or less. By making the content of the binder above the lower limit, the positive electrode active material can be stably maintained. In addition, by making the content of the binder below the upper limit, the content of the positive electrode active material particles can be increased, and the energy density can be improved.

[0077] As thickeners, for example, polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose can be cited. In the case where the thickener has a functional group that reacts with lithium or the like, the functional group can be deactivated in advance by methylation or the like. When a thickener is used, the content of the thickener in the positive electrode active material layer is preferably set to 5% by mass or less, and more preferably set to 1% by mass or less. The technology disclosed herein can be well implemented in a form where the positive electrode active material layer does not contain a thickener.

[0078] The filler is not particularly limited. As fillers, polyolefins such as polypropylene and polyethylene can be cited; inorganic oxides such as silicon dioxide, aluminum oxide, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, aluminum silicate, etc.; hydroxides such as magnesium hydroxide, calcium hydroxide, aluminum hydroxide; carbon dioxide salts such as calcium carbonate; insoluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate; nitrides such as aluminum nitride and silicon nitride, insoluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate; talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica, etc. Mineral resource-derived materials or these artificial products, etc. When a filler is used, the content of the filler in the positive electrode active material layer is preferably set to 5% by mass or less, and more preferably set to 1% by mass or less. The technology disclosed here can also be well implemented in the form where the positive electrode active material layer does not contain a filler.

[0079] The positive 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, Nb, and W as components other than conductive agents, binders, thickeners, and fillers.

[0080] <Method for producing positive electrode for non-aqueous electrolyte storage device>

[0081] The preparation of the above-mentioned positive electrode can be carried out, for example, by directly coating the positive electrode mixture paste on the positive electrode substrate or coating the positive electrode mixture paste via an intermediate layer and drying it. The positive electrode mixture paste can include the first positive electrode active material particles, the second positive electrode active material particles, the conductive agent, and the binder of any component, etc., which constitute the positive electrode active material layer. The positive electrode mixture paste usually also includes a dispersant. As a dispersant for modulating the positive electrode mixture paste, N-methylpyrrolidone (NMP), toluene, etc. can be cited.

[0082] <Non-aqueous electrolyte energy storage device>

[0083] A nonaqueous electrolyte storage element (hereinafter, also referred to as "storage element") according to one embodiment of the present invention comprises: an electrode body having a positive electrode, a negative electrode and a separator, a nonaqueous electrolyte, and a container for accommodating the electrode body and the nonaqueous electrolyte. The electrode body is usually 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 wound in a state in which they are stacked via a separator. The nonaqueous electrolyte exists in a state impregnated in the positive electrode, the negative electrode and the separator. As an example of a nonaqueous electrolyte storage element, a nonaqueous electrolyte secondary battery (hereinafter, also referred to as "secondary battery") is described.

[0084] (positive electrode)

[0085] The positive electrode used in the nonaqueous electrolyte energy storage device according to one embodiment of the present invention is the positive electrode for the nonaqueous electrolyte energy storage device according to one embodiment of the present invention described above.

[0086] (negative electrode)

[0087] The negative electrode comprises a negative electrode substrate and a negative electrode active material layer provided directly on the negative electrode substrate 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.

[0088] The negative electrode substrate has conductivity. As the material of the negative electrode substrate, metals such as copper, nickel, stainless steel, nickel-plated steel, aluminum, or alloys of these metals, carbonaceous materials, etc. are used. Among these, copper or copper alloys are preferred. As the negative electrode substrate, foil, vapor-deposited film, net, porous material, etc. can be cited, and from the viewpoint of cost, foil is preferred. Therefore, copper foil or copper alloy foil is preferably used as the negative electrode substrate. Examples of copper foil include rolled copper foil, electrolytic copper foil, etc.

[0089] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, further preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By making the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased, and the energy density per unit volume of the non-aqueous electrolyte storage element can be increased.

[0090] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains any component such as a conductive agent, a binder, a thickener, and a filler as needed. The conductive agent, the binder, the thickener, the filler, and any component can be selected from the materials exemplified for the positive electrode.

[0091] The negative electrode active material layer may 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, transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W as ingredients other than the negative electrode active material, conductive agent, binder, thickener and filler.

[0092] As the negative electrode active material, it can be appropriately selected from known negative electrode active materials. As the negative electrode active material for lithium ion secondary batteries, materials that can embed and de-embed lithium ions are generally used. Examples of the negative electrode active material 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 , LiTiO2, TiNb2O7 and other titanium-containing oxides; polyphosphorus compounds; silicon carbide; carbon materials such as graphite (graphite), non-graphite carbon (graphitizable carbon or non-graphitizable carbon), etc. Among these materials, graphite and non-graphite carbon are preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more of them may be mixed and used.

[0093] “Graphite” refers to the average lattice spacing (d) of the (002) plane determined by X-ray diffraction before charge / 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.

[0094] “Non-graphite carbon” refers to a carbon material having an average lattice plane spacing (d002) of 0.34 nm to 0.42 nm on the (002) plane determined by X-ray diffraction before charge and discharge or in a discharged state. Examples of non-graphite carbon include difficult-graphitizable carbon and easily-graphitizable carbon. Examples of non-graphite carbon include materials derived from resins, petroleum asphalt or materials derived from petroleum asphalt, petroleum coke or materials derived from petroleum coke, materials derived from plants, materials derived from alcohols, and the like.

[0095] Here, the "discharge state" refers to a discharge state in which lithium ions that can be inserted and removed during charging and discharging are fully removed from the carbon material as the negative electrode active material. For example, it is a state in which the open circuit voltage is 0.7V or more in a half-cell using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metal Li as a counter electrode.

[0096] "Non-graphitizable carbon" refers to the above-mentioned 002 It is a carbon material with a diameter of 0.36nm to 0.42nm.

[0097] "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.

[0098] The negative electrode active material is usually a particle (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-containing oxide or a polyphosphate compound, the average particle size can be 1 μm to 100 μm. When the negative electrode active material is Si, Sn, Si oxide or Sn oxide, etc., the average particle size can also be 1 nm to 1 μm. By making the average particle size of the negative electrode active material above the above lower limit, the manufacture or handling of the negative electrode active material becomes easy. By making the average particle size of the negative electrode active material below the above upper limit, the electronic conductivity of the negative electrode active material layer is improved. In order to obtain a specified powder particle size, a pulverizer, a classifier, etc. are 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.

[0099] The negative electrode active material content of the negative electrode active material layer is preferably 60 to 99 mass %, more preferably 90 to 98 mass %. By setting the negative electrode active material content within the above range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0100] (Isolator)

[0101] The separator can be appropriately selected from known separators. As the separator, for example, a separator consisting only of a substrate layer can be used, and a separator in which a heat-resistant layer containing heat-resistant particles and an adhesive is formed on one surface or both surfaces of the substrate layer can be used. As the shape of the substrate layer of the separator, for example, woven fabrics, non-woven fabrics, porous resin films, etc. 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, polyolefins such as polyethylene and polypropylene are preferred, and from the viewpoint of anti-oxidative decomposition, polyimides, aromatic polyamides, etc. are preferred. As the substrate layer of the separator, a material obtained by compounding these resins can also be used.

[0102] The heat-resistant particles contained in the heat-resistant layer are preferably heat-resistant particles whose mass reduction is 5% or less when the temperature is increased from room temperature to 500°C in an air atmosphere at 1 atmosphere pressure, and more preferably heat-resistant particles whose mass reduction is 5% or less when the temperature is increased from room temperature to 800°C. Inorganic compounds can be cited as materials whose mass reduction is less than a specified amount. As inorganic compounds, for example, oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, aluminum silicate, etc.; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; insoluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; substances derived from mineral resources such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. As the inorganic compound, a single substance or a composite of these substances may be used alone, or two or more of them may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide or aluminum silicate is preferred from the viewpoint of safety of the non-aqueous electrolyte storage element.

[0103] 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, the "porosity" refers to a value based on volume, and is a value measured using a mercury porosimeter.

[0104] As a separator, a polymer gel composed of a polymer and a non-aqueous electrolyte can be used. As polymers, for example, polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinyl pyrrolidone, polyvinylidene fluoride, etc. can be cited. If a polymer gel is used, it has the effect of suppressing leakage. As a separator, the above-mentioned porous resin film or non-woven fabric can be used together with the polymer gel.

[0105] (Non-aqueous electrolyte)

[0106] The non-aqueous electrolyte may be appropriately selected from known non-aqueous electrolytes. Among the non-aqueous electrolytes, a non-aqueous electrolyte solution may be used. The non-aqueous electrolyte solution includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0107] As the non-aqueous solvent, it is possible to appropriately select from known non-aqueous solvents. As the non-aqueous solvent, cyclic carbonate, chain carbonate, carboxylate, phosphoric acid ester, sulfonic acid ester, ether, amide, acrylonitrile-butadiene rubber etc. can be used. As the non-aqueous solvent, it is possible to use a solvent in which a part of the hydrogen atoms included in these compounds is replaced by halogen.

[0108] Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene 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.

[0109] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethylmethyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, EMC is preferred.

[0110] 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 kept low. When a cyclic carbonate and a chain carbonate are used, the volume ratio of the cyclic carbonate and the chain carbonate (cyclic carbonate: chain carbonate) is preferably in the range of 5:95 to 50:50, for example.

[0111] The electrolyte salt may be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Among these, lithium salts are preferred.

[0112] As lithium salts, inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2 can be cited; lithium oxalate salts such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); lithium salts having halogenated hydrocarbon groups such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3 can be cited. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0113] The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / dm 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 / dm3 ~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 can be improved.

[0114] In addition to the non-aqueous solvent and the electrolyte salt, the non-aqueous electrolyte may also contain additives. Examples of the additives include aromatic compounds such as biphenyl, alkylbiphenyl, triphenyl, partially hydrogenated triphenyl, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl ether, and diphenylfuran; 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, methyl vinylene carbonate, ethyl vinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutamic anhydride, itaconic anhydride, and cyclohexanedicarbonic anhydride; vinyl sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, butyl dimethanesulfonate Ester (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-dioxa-1,3,2-dioxatetrahydrothiophene), 4-methylsulfonyloxymethyl-2,2-dioxa-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, bispyridine disulfide, 1,3-propylene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl borate, tetratrimethylsilyl borate, monofluoro lithium phosphate, difluoro lithium phosphate, etc. These additives may be used alone or in combination of two or more.

[0115] The content of the additive contained 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 cycle performance after high temperature storage can be improved, and the safety can be further improved.

[0116] 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.

[0117] The solid electrolyte can be selected from any material that is ion conductive and 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.

[0118] In the case of lithium ion secondary batteries, examples of sulfide solid electrolytes include Li2S-P2S5, LiI-Li2S-P2S5, Li 10 Ge-P2S 12 wait.

[0119] The shape of the nonaqueous electrolyte storage element of the present embodiment is not particularly limited, and examples thereof include cylindrical batteries, square batteries, flat batteries, coin batteries, button batteries, and the like.

[0120] Figure 1 , a storage element 1 as an example of a square battery is shown. It should be noted that this figure is a perspective view of the inside of a container. An electrode body 2 having a positive electrode and a negative electrode wound with a separator interposed therebetween is housed in a square container 3. The positive electrode is electrically connected to a positive terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative terminal 5 via a negative electrode lead 51.

[0121] <Electricity storage device>

[0122] The non-aqueous electrolyte storage element of the present embodiment is a storage device of a storage unit (battery module) composed of a plurality of non-aqueous electrolyte storage elements, and can be mounted on a power source for vehicles such as electric vehicles (EV), hybrid vehicles (HEV), plug-in hybrid electric vehicles (PHEV), a power source for electronic devices such as personal computers and communication terminals, or a power source for power storage, etc. In this case, the technology of the present invention can be applied to at least one storage element included in the storage unit.

[0123] Figure 2 The figure shows an example in which the storage unit 20 formed by collecting two or more electrically connected non-aqueous electrolyte storage elements 1 is further collected to form a storage device 30. The storage device 30 may include a bus bar (not shown) that electrically connects the two or more non-aqueous electrolyte storage elements 1, a bus bar (not shown) that electrically connects the two or more storage units 20, etc. The storage unit 20 or the storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more non-aqueous electrolyte storage elements.

[0124] <Method for manufacturing energy storage device>

[0125] The manufacturing method of the non-aqueous electrolyte storage element of the present embodiment can be appropriately selected from known methods. The manufacturing method, for example, comprises: a process of preparing an electrode body and a non-aqueous electrolyte and a process of storing the electrode body and the non-aqueous electrolyte in a container. The process of preparing the electrode body includes: a process of preparing a positive electrode and a negative electrode and a process of forming an electrode body by stacking or winding the positive electrode and the negative electrode via a separator.

[0126] The step of 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 in the container and then the injection port can be sealed.

[0127] <Other embodiments>

[0128] It should be noted that the non-aqueous electrolyte storage element of the present invention is not limited to the above-mentioned embodiment, and various changes can be added within the scope of the gist of the present invention. For example, the structure of other embodiments can be added to the structure of a certain embodiment, and a part of the structure of a certain embodiment can be replaced with the structure of other embodiments or known technology. And a part of the structure of a certain embodiment can be removed. In addition, a known technology can be added to a certain embodiment.

[0129] In the above-mentioned embodiment, the case where the nonaqueous electrolyte storage element is used as a rechargeable nonaqueous electrolyte secondary battery (e.g., a lithium ion secondary battery) is described, but the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The present invention is also applicable to capacitors such as various secondary batteries, double-layer capacitors, or lithium ion capacitors.

[0130] In the above embodiment, the positive electrode and the negative electrode are stacked with a separator, but the electrode body may not have a separator. For example, the positive electrode and the negative electrode may be directly connected to the active material layer of the positive electrode or the negative electrode by forming a non-conductive layer on the active material layer of the positive electrode or the negative electrode.

[0131] Example

[0132] The present invention will be described in more detail below based on examples. However, the present invention is not limited to the following examples.

[0133] [Example 1]

[0134] (Production of positive electrode)

[0135] As the positive electrode active material particles, LiNi 0.8 Co 0.1 Mn 0.1 O2 single particle system particle A and LiNi 0.8 Co 0.1 Mn0.1 Secondary particles B of O2. In addition, CNT (average diameter of 10nm, average length of 25μm) belonging to fibrous carbon was used as a conductive agent, and polyvinylidene fluoride (PVDF) was used as a binder. A positive electrode mixture paste was prepared by adding an appropriate amount of N-methyl-pyrrolidone (NMP) belonging to a dispersant to a mixture of positive electrode active material particles (the total of single-particle system particles A and secondary particles B) and a conductive agent and a binder in a mass ratio of 98.3:0.5:1.2 converted to solid content. The positive electrode mixture paste was applied to the surface of the aluminum foil of the positive electrode substrate and dried to prepare a positive electrode active material layer. Then roll pressing was performed to obtain a positive electrode. The average primary particle size and average secondary particle size of the first positive electrode active material particles (positive electrode active material particles with a Feret diameter of less than 5μm) and the second positive electrode active material particles (positive electrode active material particles with a Feret diameter greater than 5μm) contained in the above-mentioned positive electrode active material layer are shown in Table 1.

[0136] (Production of negative electrode)

[0137] A negative electrode mixture paste is prepared by adding an appropriate amount of water as a dispersant to a mixture of graphite, a negative electrode active material, styrene butadiene rubber (SBR), a binder, and carboxymethyl cellulose (CMC), a thickener, in a mass ratio of 98.0:1.0:1.0 in terms of solid content. The negative electrode mixture paste is applied to the surface of the copper foil of the negative electrode substrate and dried to prepare a negative electrode active material layer. Then, roll pressing is performed to obtain a negative electrode.

[0138] (Assembly of non-aqueous electrolyte storage element)

[0139] An electrode body was prepared using the positive electrode, the negative electrode, and a polyolefin microporous membrane as a separator. The electrode body was placed in a container and injected with a non-aqueous electrolyte, thereby assembling the non-aqueous electrolyte storage element of Example 1. It should be noted that as a non-aqueous electrolyte, lithium hexafluorophosphate (LiPF6) as an electrolyte salt was used in a non-aqueous solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 30:35:35. 3 The concentration of the dissolved solution.

[0140] [Comparative Example 1 and Reference Examples 1 to 4]

[0141] The types of the first positive electrode active material particles and the second positive electrode active material particles, the average primary particle size and the average secondary particle size, the type of the conductive agent, and the content of the conductive agent in the solid component of the positive electrode mixture paste (i.e., the content of the conductive agent in the formed positive electrode active material layer) are shown in Table 1. In addition, the content of the binder was made the same as in Example 1, and the content of the conductive agent and the content of the positive electrode active material particles were adjusted. Except for these points, each non-aqueous electrolyte storage element of Comparative Example 1 and Reference Examples 1 to 4 was prepared in the same manner as Example 1. It should be noted that the second positive electrode active material particles contained in the positive electrode active material layer of each non-aqueous electrolyte storage element of Reference Examples 3 and 4 are particles of the same size, but these average primary particle sizes and average secondary particle sizes were not measured. In addition, "AB" in Table 1 represents acetylene black.

[0142] [evaluate]

[0143] (Initial discharge capacity)

[0144] For each non-aqueous electrolyte storage element, a discharge capacity confirmation test was performed under the following conditions. After constant current charging at 4.25V at 25°C with a charging current of 0.1C, constant voltage charging was performed at 4.25V. The end condition of charging was when the charging current reached 0.05C. After a 10-minute rest after charging, constant current discharge was performed at 25°C with a discharge current of 0.2C until 2.75V was reached. The discharge capacity at this time was referred to as the "initial discharge capacity".

[0145] (Charge and discharge cycle test)

[0146] The following charge and discharge cycle test was carried out for each non-aqueous electrolyte storage element obtained. After being stored in a thermostatic chamber at 45°C for 2 hours, constant current charging was performed at a charging current of 1.0C until 4.25V, and then constant voltage charging was performed at 4.25V. The end condition of charging is to make the total charging time reach 3 hours. Then a 10-minute rest period was set. Constant current discharge was performed until the discharge current of 1.0C reached 2.75V, and then a 10-minute rest period was set. These charging and discharging processes were regarded as 1 cycle, and the cycle was implemented 1000 times. These charging, discharging and resting were carried out in a thermostatic chamber at 45°C.

[0147] (Capacity maintenance rate)

[0148] After the above-mentioned charge and discharge cycle test, the discharge capacity after the charge and discharge cycle test was measured for each non-aqueous electrolyte storage element under the same conditions as the above-mentioned initial discharge capacity. The percentage of the discharge capacity after the charge and discharge cycle test relative to the initial discharge capacity was calculated as the capacity retention rate. For the capacity retention rate, non-aqueous electrolyte storage elements with the same type and average particle size of each positive electrode active material particle constituting the positive electrode active material layer were compared. Specifically, among the non-aqueous electrolyte storage elements with the same type and average particle size of each positive electrode active material particle constituting the positive electrode active material layer, the capacity retention rate of the non-aqueous electrolyte storage element with a conductive agent content of 4.0% was used as a reference (100.0%), and the ratio of the capacity retention rates of other non-aqueous electrolyte storage elements was calculated as the capacity retention rate ratio (%). More specifically, the capacity retention rate ratio of Comparative Example 1 is a value based on Reference Example 1 as a reference (100.0%). The capacity retention rate ratio of Example 1 is a value based on Reference Example 2 as a reference (100.0%). The capacity maintenance ratio of Reference Example 4 is a value based on Reference Example 3 (100.0%).

[0149] The results are shown in Table 1.

[0150]

[0151] If the non-aqueous electrolyte storage element of Reference Example 1 in which the so-called small-particle first positive electrode active material particle is not a single-particle particle is compared with the non-aqueous electrolyte storage element of Comparative Example 1, it can be seen that the capacity retention rate of the non-aqueous electrolyte storage element of Comparative Example 1 with a small content of the conductive agent in the positive electrode active material layer after the charge-discharge cycle test is greatly reduced (the capacity retention rate ratio is small). In contrast, if the non-aqueous electrolyte storage element of Reference Example 2 in which the first positive electrode active material particle is a single-particle particle is compared with the non-aqueous electrolyte storage element of Example 1, it can be seen that the reduction in the capacity retention rate after the charge-discharge cycle test of the non-aqueous electrolyte storage element of Example 1, which occurs when the content of the conductive agent in the positive electrode active material layer is reduced, is suppressed compared with Comparative Example 1 in which the first positive electrode active material particle is not a single-particle particle.

[0152] In addition, it can be seen that, for the non-aqueous electrolyte storage element of Reference Example 4, when the content of the conductive agent in the positive electrode active material layer is 1.1 mass %, the phenomenon of reduced capacity retention rate after charge and discharge cycles will not occur, while for the non-aqueous electrolyte storage element of Comparative Example 1, when the content of the conductive agent in the positive electrode active material layer is less than 1.1 mass %, the phenomenon of reduced capacity retention rate after charge and discharge cycles will occur.

[0153] Explanation of symbols

[0154] 1Non-aqueous electrolyte storage element

[0155] 2-electrode body

[0156] 3 Containers

[0157] 4 Positive terminal

[0158] 41 positive lead

[0159] 5 Negative terminal

[0160] 51 negative lead

[0161] 20 Storage Unit

[0162] 30 Power storage device

Claims

1. A positive electrode for a non-aqueous electrolyte storage element, comprising a positive electrode active material layer, The positive electrode active material layer contains: first positive electrode active material particles having a Feret diameter of 5 μm or less according to a projection image observed by a scanning electron microscope (SEM), second positive electrode active material particles having a Feret diameter of more than 5 μm according to a projection image observed by the SEM, and a conductive agent; The content of the conductive agent in the positive electrode active material layer is less than 1.1% by mass. The first positive electrode active material particles are secondary particles having a ratio of an average secondary particle size to an average primary particle size of 3 or less, or primary particles that are substantially not aggregated.

2. The positive electrode according to claim 1, wherein The conductive agent is fibrous carbon.

3. The positive electrode according to claim 1 or 2, wherein The first positive electrode active material particles have an average primary particle size of 2.8 μm or more.

4. The positive electrode according to claim 1 or 2, wherein The first positive electrode active material particles include a transition metal composite oxide containing nickel.

5. A non-aqueous electrolyte storage element, wherein: A positive electrode according to claim 1 or 2.

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