Positive electrode for nonaqueous electrolyte power storage element, nonaqueous electrolyte power storage element, and power storage device

Abstract

A positive electrode for a nonaqueous electrolyte power storage element according to one embodiment of the present invention is provided with a positive electrode base material and a positive electrode active material layer that is directly laminated on the positive electrode base material. The positive electrode active material layer contains a conductive agent and a polyanion compound including elemental iron. The average particle size of the polyanion compound is 2.5 µm or less. In the surface of the positive electrode active material layer facing the positive electrode base material, the existence ratio of the conductive agent with respect to all components in the positive electrode active material layer is 30-90%.

Description

Positive electrode for non-aqueous electrolyte energy storage element, non-aqueous electrolyte energy storage element, and energy storage device

[0001] The present invention relates to a positive electrode for a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte energy storage element, and an energy storage device.

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, are widely used in electronic devices like personal computers and communication terminals, as well as in automobiles, due to their high energy density. Generally, non-aqueous electrolyte secondary batteries consist of a pair of electrodes electrically isolated by a separator, with a non-aqueous electrolyte interposed between these electrodes. They are configured to charge and discharge by transferring charge-transporting ions between the two electrodes. In addition to non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double-layer capacitors are also widely used as non-aqueous electrolyte energy storage elements.

[0003] Polyanionic compounds containing iron elements, such as lithium iron phosphate, are known as one of the positive electrode active materials used in non-aqueous electrolyte energy storage devices (Patent Document 1).

[0004] International Publication No. 2023 / 090453

[0005] The positive electrode of a non-aqueous electrolyte energy storage element is typically fabricated by laminating a positive electrode active material layer containing a positive electrode active material onto a positive electrode substrate. When using a polyanionic compound containing iron as the positive electrode active material, an intermediate layer containing a conductive material or the like may be provided on the positive electrode substrate to reduce contact resistance between the positive electrode substrate and the positive electrode active material layer and improve output performance.

[0006] However, adding such an intermediate layer can increase the manufacturing cost of non-aqueous electrolyte energy storage elements. Even if the positive electrode active material layer is laminated on the positive electrode substrate without an intermediate layer, one way to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer is to increase the average particle size of the polyanionic compound containing iron. However, increasing the average particle size of the polyanionic compound containing iron tends to decrease the pressability of the positive electrode active material layer (how easily the positive electrode active material layer can be made denser by pressing). If the pressability of the positive electrode active material layer is low, the energy density of the non-aqueous electrolyte energy storage element may decrease.

[0007] The object of the present invention is to provide a positive electrode for a non-aqueous electrolyte energy storage element that uses a polyanion compound containing an iron element, facilitates high density of the positive electrode active material layer, and reduces the resistance of the non-aqueous electrolyte energy storage element, as well as a non-aqueous electrolyte energy storage element and an energy storage device equipped with such a positive electrode for a non-aqueous electrolyte energy storage element.

[0008] A positive electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a positive electrode substrate and a positive electrode active material layer directly laminated on the positive electrode substrate, wherein the positive electrode active material layer contains a polyanionic compound containing an iron element and a conductive agent, the average particle size of the polyanionic compound is 2.5 μm or less, and on the surface of the positive electrode active material layer facing the positive electrode substrate, the ratio of the conductive agent to the total components in the positive electrode active material layer is 30% to 90%.

[0009] A non-aqueous electrolyte energy storage element according to another aspect of the present invention comprises a positive electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention.

[0010] A further embodiment of the present invention comprises two or more energy storage elements and one or more non-aqueous electrolyte energy storage elements according to one aspect of the present invention.

[0011] According to one aspect of the present invention, a positive electrode for a non-aqueous electrolyte energy storage element is provided, which uses a polyanion compound containing an iron element, facilitates high-density formation of the positive electrode active material layer, and reduces the resistance of the non-aqueous electrolyte energy storage element. A non-aqueous electrolyte energy storage element and an energy storage device equipped with such a positive electrode for a non-aqueous electrolyte energy storage element can be provided.

[0012] Figure 1 is a perspective view showing a non-aqueous electrolyte energy storage element equipped with a positive electrode for a non-aqueous electrolyte energy storage element according to one embodiment of the present invention. Figure 2 is a schematic diagram showing an energy storage device equipped with multiple non-aqueous electrolyte energy storage elements according to one embodiment of the present invention.

[0013] First, an overview of the positive electrode for a non-aqueous electrolyte energy storage element and the non-aqueous electrolyte energy storage element disclosed herein will be described.

[0014] [1] A positive electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a positive electrode substrate and a positive electrode active material layer directly laminated on the positive electrode substrate, wherein the positive electrode active material layer contains a polyanionic compound containing an iron element and a conductive agent, the average particle size of the polyanionic compound is 2.5 μm or less, and on the surface of the positive electrode active material layer facing the positive electrode substrate, the ratio of the conductive agent to the total components in the positive electrode active material layer is 30% or more and 90% or less.

[0015] The positive electrode for the non-aqueous electrolyte energy storage element described in [1] above (hereinafter also simply referred to as "positive electrode") uses a polyanionic compound containing iron, making it easy to increase the density of the positive electrode active material layer and reduce the resistance of the non-aqueous electrolyte energy storage element. The reason for this is not clear, but the following reasons are speculated. The positive electrode active material layer is usually formed by applying a positive electrode mixture to a positive electrode substrate and then pressing it. Increasing the pressure used to press the positive electrode mixture can increase the density of the positive electrode active material layer, but it may also cause the positive electrode active material layer to rupture. Conversely, lowering the pressure used to press the positive electrode mixture can suppress the rupture of the positive electrode active material layer, but it may also result in a lower density of the positive electrode active material layer. In contrast, in the positive electrode described in [1] above, since the average particle size of the polyanionic compound containing iron is 2.5 μm or less, a high-density positive electrode active material layer can be formed even when pressed at a relatively low pressure. In other words, the positive electrode active material layer of the positive electrode described in [1] above has high pressability. In the positive electrode described in [1] above, no intermediate layer is provided between the positive electrode substrate and the positive electrode active material layer, and the positive electrode active material layer is directly laminated to the positive electrode substrate. In conventional positive electrodes using polyanionic compounds containing iron, when the positive electrode active material layer is directly laminated to the positive electrode substrate, the contact resistance between the positive electrode substrate and the positive electrode active material layer may not be sufficiently low, especially when the average particle size of the polyanionic compound containing iron is small. In contrast, in the positive electrode described in [1] above, the ratio of conductive agent to the total components in the positive electrode active material layer is 30% to 90% on the surface of the positive electrode active material layer facing the positive electrode substrate, so the contact resistance between the positive electrode substrate and the positive electrode active material layer can be reduced. Therefore, the positive electrode described in [1] above allows for easy densification of the positive electrode active material layer and can reduce the resistance of the non-aqueous electrolyte energy storage element.

[0016] The ratio of the conductive agent to the total components in the positive electrode active material layer on the surface of the positive electrode active material layer facing the positive electrode substrate is calculated by the following procedure: The positive electrode is processed by ion milling to expose cross-sections of the parts where the positive electrode substrate and the positive electrode active material layer face each other at five arbitrary locations. These cross-sections are observed with an EPMA (Electron Probe Micro Analyzer), and the contact length of each component in the positive electrode active material layer on the surface facing the positive electrode substrate is measured. For each cross-section, the ratio of the contact length of the conductive agent to the sum of the contact lengths of each component in the positive electrode active material layer is calculated. The average value of the ratio of the contact length of the conductive agent to the sum of the contact lengths of each component in the positive electrode active material layer at the five cross-sections is calculated and taken as the ratio of the conductive agent to the total components in the positive electrode active material layer on the surface of the positive electrode active material layer facing the positive electrode substrate. Note that the carbon material coating the positive electrode active material, as described later, is not included in the conductive agent here, but is included in the positive electrode active material. Furthermore, according to the inventors' knowledge, the contact resistance between the positive electrode substrate and the positive electrode active material layer is not easily reduced by the carbon material coating the positive electrode active material. Moreover, when observing the cross-section of the portion where the positive electrode substrate and the positive electrode active material layer face each other using EPMA, it is difficult to observe the carbon material coating the positive electrode active material at a nano-order thickness. In other words, the proportion of the conductive agent calculated by the procedure for observing the cross-section using EPMA does not include the proportion of the carbon material coating the positive electrode active material. Processing by ion milling is performed on the positive electrode before it is incorporated into the non-aqueous electrolyte energy storage element, or, for positive electrodes incorporated into the non-aqueous electrolyte energy storage element, it is performed on those processed using the following procedure. First, the non-aqueous electrolyte energy storage element is charged with a charging current of 0.05C until it reaches the charging termination voltage for normal use, and is brought to a fully charged state. After a 30-minute pause, the device is discharged at a constant current of 0.05C until it reaches the discharge termination voltage for normal use. "Normal use" refers to using the non-aqueous electrolyte energy storage element under the recommended or specified charge / discharge conditions, and, if equipment for using the non-aqueous electrolyte energy storage element is available, using that equipment.A non-aqueous electrolyte energy storage element is disassembled, the positive electrode is removed, and a test battery is assembled using the removed positive electrode as the working electrode and a metallic lithium electrode as the counter electrode. Pure metallic lithium is used for the metallic lithium electrode. For the test battery, with a current of 10 mA per gram of positive electrode active material, the positive electrode potential is 2.0 V (vs. Li / Li). ＋ Constant current discharge is performed until the positive electrode is fully discharged. The device is disassembled again, and the positive electrode is removed. The removed positive electrode is washed with dimethyl carbonate. This positive electrode is then subjected to processing by the ion milling method. The disassembly of the non-aqueous electrolyte energy storage element and the washing with dimethyl carbonate are carried out in an argon atmosphere with a dew point of -60°C or lower.

[0017] The "average particle size" of a polyanionic compound containing iron is defined in accordance with JIS-Z-8825 (2013), based on the particle size distribution measured by laser diffraction / scattering on a dilution of the polyanionic compound diluted in a solvent. The value at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001) reaches 50% (D50: median diameter). It has been confirmed that the average particle size based on the above measurement is in close agreement with the average secondary particle diameter, which is the average value of the particle diameters of each secondary particle measured by extracting 50 particles from an image observed using a scanning electron microscope (SEM) of the polyanionic compound (hereinafter also referred to as "SEM image"), while avoiding extremely large and extremely small particles. The particle diameter of each secondary particle based on the measurement from this SEM image is determined as follows. The shortest diameter passing through the center of the smallest circumscribed circle of each secondary particle is defined as the minor axis, and the diameter passing through the same center and perpendicular to the minor axis is defined as the major axis. The average value of the major axis and minor axis is defined as the particle diameter of each secondary particle. If there are two or more shortest diameters, the longest perpendicular diameter is defined as the minor axis.

[0018] The average particle size is measured on the polyanion compound extracted from a positive electrode before it is incorporated into a non-aqueous electrolyte energy storage element, or a positive electrode incorporated into a non-aqueous electrolyte energy storage element, processed according to the procedure described in the ion milling method described above. The positive electrode active material layer is peeled off from the positive electrode substrate, and the positive electrode active material layer is washed with a solvent capable of dissolving the binder to remove the binder. Then, it is washed with water and dried under reduced pressure at room temperature for 24 hours to obtain the polyanion compound. The obtained polyanion compound is then subjected to measurement. The process from peeling off the positive electrode active material layer to obtaining the polyanion compound is carried out in an argon atmosphere with a dew point of -60°C or lower. The average particle size of the polyanion compound measured in this way is the average particle size in the state in which it is contained in the positive electrode active material layer. In other words, the average particle size of the polyanion compound is usually the average particle size of the polyanion compound contained in the positive electrode active material layer formed by pressing the positive electrode mixture. For example, if the fracture strength of the polyanionic compound contained in the positive electrode mixture is low, the polyanionic compound can be pulverized by pressing the positive electrode mixture. Therefore, the average particle size of the polyanionic compound in the present invention (average particle size after pressing the positive electrode mixture) may be smaller than that at the time of preparation of the positive electrode mixture.

[0019] The statement that the positive electrode active material layer is "directly laminated to the positive electrode substrate" means that there is no intermediate layer containing a conductive material such as carbon between the positive electrode substrate and the positive electrode active material layer. In other words, for example, if a carbon-coated foil with a carbon coating layer on the positive electrode substrate is used, the positive electrode active material layer is excluded from the state of being "directly laminated to the positive electrode substrate." As mentioned above, providing an intermediate layer on the positive electrode substrate can increase the manufacturing cost of the non-aqueous electrolyte energy storage element. Note that when an intermediate layer containing a conductive agent is provided between the positive electrode substrate and the positive electrode active material layer, the ratio of the conductive agent to the total components in the intermediate layer on the surface of the intermediate layer facing the positive electrode substrate is usually more than 90%. The "ratio of conductive agent to all components in the intermediate layer on the surface of the intermediate layer facing the positive electrode substrate" is obtained by processing the positive electrode by ion milling using the same procedure as described above, exposing the cross-sections of the positive electrode substrate and the intermediate layer at five arbitrary locations, observing these cross-sections with EPMA, measuring the contact length of each component in the intermediate layer that is in contact with the positive electrode substrate, calculating the ratio of the contact length of the conductive agent to the sum of the contact lengths of each component in the intermediate layer, and calculating the average value of the ratio of the contact length of the conductive agent to the sum of the contact lengths of each component in the intermediate layer at the five cross-sections.

[0020] [2] In the positive electrode for a non-aqueous electrolyte energy storage element described in [1] above, the positive electrode substrate may be a non-roughened substrate.

[0021] The positive electrode for the non-aqueous electrolyte energy storage element described in [2] above is a non-roughened substrate that has not undergone surface roughening treatment, thus reducing manufacturing costs. Generally, using a roughened substrate tends to increase adhesion between the positive electrode substrate and the positive electrode active material layer, thus reducing contact resistance between the positive electrode substrate and the positive electrode active material layer, but this can increase manufacturing costs. In contrast, the positive electrode for the non-aqueous electrolyte energy storage element described in [2] above can easily reduce the resistance of the non-aqueous electrolyte energy storage element without using a roughened substrate as the positive electrode substrate. In other words, the positive electrode for the non-aqueous electrolyte energy storage element described in [2] above can particularly significantly achieve the effect of the present invention, which is to reduce the resistance of the non-aqueous electrolyte energy storage element, while reducing manufacturing costs.

[0022] A "non-roughened substrate" refers to a substrate in which the arithmetic mean roughness Ra on the surface facing the positive electrode active material layer is 0.1 μm or less. The arithmetic mean roughness Ra is the average value of values ​​measured at five arbitrary locations, in accordance with JIS-B-0601 (2013).

[0023] [3] In the positive electrode for a non-aqueous electrolyte energy storage element described in [1] or [2] above, the content of the conductive agent in the positive electrode active material layer may be 10.0% by mass or less.

[0024] The positive electrode for non-aqueous electrolyte energy storage elements described in [3] above has a conductive agent content of 10.0% by mass or less in the positive electrode active material layer, making it easier to ensure the flexibility of the positive electrode active material layer and providing high pressability. For this reason, the positive electrode for non-aqueous electrolyte energy storage elements described in [4] above makes it easier to increase the density of the positive electrode active material layer. In addition, the positive electrode for non-aqueous electrolyte energy storage elements described in [4] above allows for a relatively larger proportion of the positive electrode active material in the positive electrode active material layer, thus increasing the energy density.

[0025] [4] A non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a positive electrode for a non-aqueous electrolyte energy storage element as described in any of [1] to [3] above.

[0026] The non-aqueous electrolyte energy storage element described in [4] above is equipped with a positive electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention, and therefore a polyanionic compound containing an iron element is used, making it easy to increase the density of the positive electrode active material layer and reducing the resistance of the non-aqueous electrolyte energy storage element.

[0027] [5] Another embodiment of the present invention is a power storage device comprising two or more power storage elements and one or more non-aqueous electrolyte power storage elements as described in [4] above.

[0028] The energy storage device described in [5] above includes one or more non-aqueous electrolyte energy storage elements described in [4] above, thus reducing resistance.

[0029] <Positive Electrode for Non-Aqueous Electrolyte Energy Storage Element> The positive electrode (positive electrode) for a non-aqueous electrolyte energy storage element according to one embodiment of the present invention comprises a positive electrode substrate and a positive electrode active material layer directly laminated on the positive electrode substrate. Typically, the positive electrode has a portion where the positive electrode substrate is exposed. This exposed portion of the positive electrode substrate is typically connected to the positive electrode lead described above. The positive electrode may have a shape such as a sheet, plate, or strip.

[0030] The thickness of the positive electrode is set appropriately according to the application of the non-aqueous electrolyte energy storage element. The average thickness of the positive electrode may be, for example, 3 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode may be 5 μm, 10 μm, 20 μm, 30 μm, 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the positive electrode may be 500 μm, 400 μm, 300 μm, 200 μm, 150 μm, 100 μm, or 50 μm. The average thickness of the positive electrode is the average thickness of the portion on which the positive electrode active material layer is laminated on the positive electrode substrate. If there are portions on which the positive electrode active material layer is laminated on both sides of the positive electrode substrate and portions on which the positive electrode active material layer is laminated on only one side of the positive electrode substrate, then the average thickness of the portion on which the positive electrode active material layer is laminated on both sides of the positive electrode substrate shall be used. In this specification, "average thickness" means the average value of the thickness measured at any five locations.

[0031] The positive electrode substrate is conductive. In this specification, "having conductivity" means that the volume resistivity is 10 －２ This means that it is Ω·cm or less. The volume resistivity shall be the value measured in accordance with JIS-H-0505 (1975). On the other hand, in this specification, "not conductive" or "having (electrical) insulating properties" means that the above volume resistivity is 10 ７ This means it is greater than or equal to Ω·cm.

[0032] Examples of materials for the positive electrode substrate include metals such as aluminum, titanium, iron, and their alloys (stainless steel, etc.). Among these, pure aluminum or aluminum alloys are preferred from the viewpoint of high potential resistance, high electronic conductivity, and cost.

[0033] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples of positive electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The positive electrode substrate is preferably made of aluminum, and may be pure aluminum foil or aluminum alloy foil. Here, "made of aluminum" means that the aluminum content is 50% or more on a molar basis. By making the positive electrode substrate of aluminum, the adhesion between the positive electrode substrate and the positive electrode active material layer can be easily improved. This makes it easier to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. Examples of pure aluminum or aluminum alloys include A1085, A3003, and A1N30 as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0034] The positive electrode substrate is preferably a non-roughened substrate. By using a non-roughened substrate, the effect of the present invention, which is to reduce the resistance of the non-aqueous electrolyte energy storage element, can be obtained particularly significantly while reducing manufacturing costs. The arithmetic mean roughness Ra on the surface of the positive electrode substrate facing the positive electrode active material layer is 0.1 μm or less, preferably 0.08 μm or less, and more preferably 0.05 μm or less.

[0035] It is preferable that the positive electrode substrate does not have through holes. Generally, when the positive electrode substrate has through holes, the adhesion between the positive electrode substrate and the positive electrode active material layer tends to increase, and the contact resistance between the positive electrode substrate and the positive electrode active material layer tends to decrease. In contrast, by having a positive electrode substrate that does not have through holes, the effect of the present invention, which is to reduce the resistance of the non-aqueous electrolyte energy storage element, can be obtained particularly significantly while reducing manufacturing costs.

[0036] The average thickness of the positive electrode substrate may be, for example, 1 μm or more and 50 μm or less. The lower limit of the average thickness of the positive electrode substrate may be 3 μm, 5 μm, 8 μm, 10 μm, or 15 μm. The upper limit of the average thickness of the positive electrode substrate may be 40 μm, 30 μm, 20 μm, 15 μm, or 10 μm.

[0037] The positive electrode active material layer contains a polyanion compound containing iron element and a conductive agent. The positive electrode active material layer may contain optional components such as a binder, a thickener, a filler, etc. as required. The positive electrode active material layer may be formed from a positive electrode mixture containing a polyanion compound containing iron element, a conductive agent, and other optional components. The positive electrode active material layer may be provided only on one side of a positive electrode substrate having a shape such as a sheet shape, or may be provided on both sides respectively.

[0038] The polyanion compound containing iron element is a component that functions as a positive electrode active material. The polyanion compound containing iron element is composed of a polyanion (that is, a polyvalent oxoacid anion) and a cation, and usually contains an iron cation as the above cation. Further, the polyanion compound usually further contains a lithium cation as the above cation. The polyanion compound containing iron element may be composed of a polyanion, an iron cation, and a lithium cation. As the polyanion, PO ４ ３－ , SO ４ ２－ , SiO ４ ４－ , BO ３ ３－ , VO ４ ３－ etc. may be mentioned, and PO ４ ３－ (phosphate anion) is preferred. The polyanion compound containing iron element may further contain a halogen element or the like.

[0039] The polyanion compound containing iron element is preferably represented by the following formula (1). Li ａ M <00000​​​​​​... (1) In formula (1), M is one or more transition metal elements, including at least iron (Fe). A is at least one selected from B, Al, Si, P, S, Cl, Ti, V, Cr, Mo, and W. X is at least one halogen element. a, b, c, d, and e are numbers satisfying 0 < a ≤ 3, 0 < b ≤ 2, 2 ≤ c ≤ 4, 1 ≤ d ≤ 3, and 0 ≤ e ≤ 1. a, b, c, d, and e may all be integers or decimals.

[0040] The Fe content relative to the M content in formula (1) is preferably 50 mol% or more, and more preferably 70 mol% or more, 90 mol% or more, or 99 mol% or more. P is preferred as A. F is preferred as X. In one embodiment, a=1, b=1, c=4, d=1, e=0 may be preferred.

[0041] A specific example of a polyanionic compound containing iron is LiFePO4. ４ LiFe ｘ Co １－ｘ PO ４ (0<x<1), LiFe ｘ Mn １－ｘ PO ４ (0<x<1), LiFeVO ４ Li ２ FeSiO ４ Li ２ Fe ２ (SO ４ ) ３ LiFeBO ３ LiFePO ３．９ F ０．２ Examples include the following. Some atoms or polyanions in these compounds may be partially substituted with other atoms or anion species. Examples of polyanion compounds containing iron include lithium iron phosphate (LiFePO4). ４ ) is preferred. Lithium iron phosphate may be a compound in which some of the atoms or polyanions constituting lithium iron phosphate are substituted with other atoms or anion species. The polyanion compound containing iron may be used alone or in a mixture of two or more types.

[0042] Polyanionic compounds containing iron may have an olivine-type crystal structure. Compounds having an olivine-type crystal structure have a crystal structure that can be assigned to the space group Pnm. A crystal structure that can be assigned to the space group Pnm means that, in an X-ray diffraction pattern, it has a diffraction pattern that can be assigned to the space group Pnm.

[0043] The polyanionic compound containing iron may exist in the form of primary particles or secondary particles. Preferably, at least a portion of the surface of the iron-containing polyanionic compound particles is coated with a carbon material. The carbon material may be present inside (between primary particles) the secondary particles of the iron-containing polyanionic compound. The coating of the surface of the iron-containing polyanionic compound particles with a carbon material allows for good electronic conductivity.

[0044] A carbon material is a material whose main constituent element is carbon. The main constituent element is the element that is present in the largest quantity by mass. For example, the carbon content in a carbon material may be 80% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass or more, or 99.9% by mass or more. It is preferable that the carbon material is a carbon material other than a non-carbonized polymer compound. Other elements that may be included in the carbon material include oxygen, hydrogen, nitrogen, etc. Examples of carbon materials include graphite and non-graphitic carbon.

[0045] The upper limit of the average particle size of the iron-containing polyanion compound is 2.5 μm, preferably 2.0 μm, more preferably 1.8 μm, even more preferably 1.6 μm, and may also be 1.4 μm. Having an average particle size of the iron-containing polyanion compound below the above upper limit allows for higher pressability of the positive electrode active material layer and facilitates high-density construction of the positive electrode active material layer. The lower limit of the average particle size of the iron-containing polyanion compound may be 0.5 μm, 0.8 μm, or 1.0 μm. In the case of a composite in which the iron-containing polyanion compound is coated with a carbon material, the particle size of the composite is used as the average particle size of the iron-containing polyanion compound. Known methods, such as those using a pulverizer or classifier, can be employed to obtain particles with a predetermined particle size.

[0046] The average particle size of the iron-containing polyanion compound in the positive electrode active material layer can be easily adjusted to 2.5 μm or less by using an iron-containing polyanion compound (disintegrated material) with a pre-controlled (disintegrated) average particle size when preparing the positive electrode mixture. Alternatively, the average particle size of the iron-containing polyanion compound in the positive electrode active material layer may be adjusted to 2.5 μm or less by using an iron-containing polyanion compound (granulated material) with a relatively large average particle size (undisintegrated) when preparing the positive electrode mixture, and then pulverizing the granules during pressing of the positive electrode mixture. When granulated material is used as the iron-containing polyanion compound, the upper limit of the fracture strength of this polyanion compound is preferably 20 MPa, more preferably 16 MPa, and even more preferably 12 MPa. Having the fracture strength of the iron-containing polyanion compound below the above upper limit facilitates the pulverization of this polyanion compound when pressing the positive electrode mixture. In other words, the pressability of the positive electrode active material layer can be increased, and the density of the positive electrode active material layer can be easily increased. When using granules as the polyanionic compound containing iron, the lower limit of the fracture strength of this polyanionic compound may be 1 MPa, 5 MPa, or 10 MPa. The fracture strength of the polyanionic compound containing iron can be controlled by the composition of the polyanionic compound containing iron and the type of carbon material coating its surface, as well as by the manufacturing conditions such as the manufacturing method (hydrothermal method, solid-phase method, etc.) and firing conditions. Here, "fracture strength" is measured in accordance with JIS-Z-8844 (2019). The fracture strength of the granule-type polyanionic compound containing iron is measured on the particles of the iron-containing polyanionic compound before the preparation of the positive electrode mixture (undisintegrated). The fracture strength is measured on five of the above-mentioned granule-type polyanionic compound particles containing iron, and the average value is adopted.

[0047] The positive electrode active material layer may contain positive electrode active materials other than polyanionic compounds containing iron. These other positive electrode active materials can be appropriately selected from known positive electrode active materials. However, the content of the polyanionic compound containing iron relative to all positive electrode active materials in the positive electrode active material layer may be 90% to 100% by mass, or 99% to 100% by mass. The positive electrode active material layer may contain substantially only polyanionic compounds containing iron as positive electrode active materials.

[0048] The content of the iron-containing polyanion compound in the positive electrode active material layer is preferably 70% to 95% by mass, more preferably 80% to 92% by mass, and even more preferably 85% to 90% by mass. By setting the content of the iron-containing polyanion compound within the above range, it becomes easier to increase the density of the positive electrode active material layer and to further reduce the resistance of the non-aqueous electrolyte energy storage element.

[0049] The content of the positive electrode active material (total of polyanionic compounds containing iron and other positive electrode active materials) in the positive electrode active material layer is preferably 70% to 95% by mass, more preferably 80% to 92% by mass, and even more preferably 85% to 90% by mass. By setting the content of the positive electrode active material within the above range, it is easier to increase the density of the positive electrode active material layer and to further reduce the resistance of the non-aqueous electrolyte energy storage element.

[0050] Conductive agents are typically components made of conductive materials. Even if the volume resistivity of a conductive agent cannot be directly measured, the volume resistivity is 10 －２Materials whose conductivity is known to be Ω·cm or less are classified as conductive agents. Examples of conductive agents include carbon materials, metals, and conductive ceramics. However, carbon materials used to coat the particle surface of polyanionic compounds containing iron are not classified as conductive agents. A carbon material is a material whose main constituent element is carbon. The main constituent element is the element with the highest mass content. For example, the carbon content in a carbon material may be 80% by mass or more, 90% by mass or more, 95% by mass, 99% by mass, or 99.9% by mass or more. It is preferable that the carbon material is a carbon material other than a non-carbonized polymer compound. Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbons include graphene, carbon nanotubes (CNTs), and fullerenes. Conductive agents can take the form of powder or fibers. One or more conductive agents can be used. These materials may also be used in composite form as conductive agents. For example, a composite material of carbon black and CNTs may be used. Among these, carbon black is preferred, and furnace black is more preferred.

[0051] The lower limit of the conductive agent content in the positive electrode active material layer is preferably 2.5% by mass, more preferably 3.0% by mass, and may be 4.0% by mass or 5.0% by mass. When the conductive agent content in the positive electrode active material layer is above the above lower limit, sufficient conductive paths are formed within the positive electrode active material layer, further reducing the resistance of the non-aqueous electrolyte energy storage element. The upper limit of the conductive agent content in the positive electrode active material layer is preferably 10.0% by mass, more preferably 8.0% by mass, and may be 7.0% by mass, from the viewpoint of facilitating high-density construction of the positive electrode active material layer. When the conductive agent content in the positive electrode active material layer is below the above upper limit, the pressability of the positive electrode active material layer can be increased, and high-density construction of the positive electrode active material layer becomes easier.

[0052] When the conductive agent is a carbon material, the upper limit of the average length of the conductive agent may be 50 nm or 40 nm, but less than 35 nm is preferred. By keeping the average length of the conductive agent below the above upper limit, the dispersibility of the conductive agent within the positive electrode active material layer can be improved. This makes it easy to increase the ratio of the conductive agent to the total components in the positive electrode active material layer on the surface of the positive electrode active material layer facing the positive electrode substrate. The "average length of the conductive agent" refers to the average value of the major axis of each conductive agent particle, measured by extracting 50 conductive agent particles from the image (TEM image) observed using a transmission electron microscope (TEM), while avoiding extremely large and extremely small conductive agent particles. This major axis is the longest diameter passing through the center of the smallest circumscribed circle of each conductive agent particle. The average length of conductive material can be adjusted by controlling the firing temperature during the manufacturing process, changing the raw materials of the conductive material, adjusting the reaction time between the raw materials, and selecting a commercially available conductive material with the desired average length.

[0053] When the conductive agent is a carbon material, it is preferable that the conductive agent has functional groups. Examples of functional groups include hydroxyl groups, carboxyl groups, carboxylate groups, and ether groups. Having functional groups in the conductive agent can improve the dispersibility of the conductive agent within the positive electrode active material layer. This makes it easy to increase the ratio of the conductive agent to the total components in the positive electrode active material layer on the surface of the positive electrode active material layer facing the positive electrode substrate.

[0054] Examples of binders include water-based binders and organic solvent-based binders.

[0055] A water-based binder is a binder that dissolves or disperses in water. A water-based binder may be one in mass or more that dissolves or disperses in 100 parts by mass of water at 20°C. When forming a positive electrode active material layer using a positive electrode mixture paste in which the dispersion medium is water or a mixed solvent mainly composed of water, a water-based binder (a water-soluble or water-dispersible polymer material) can be used. Examples of water-based binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, and cellulose.

[0056] An organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). An organic solvent-based binder may be a binder that dissolves or disperses at 1 part by mass or more per 100 parts by mass of an organic solvent (e.g., N-methylpyrrolidone) at 20°C. When forming a positive electrode active material layer using a positive electrode mixture paste in which the dispersion medium is an organic solvent or a mixed solvent mainly composed of an organic solvent, an organic solvent-based binder (a polymer material having solubility or dispersibility in an organic solvent) can be used. Examples of organic solvent-based binders include polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide, polyimide, polyamideimide, crosslinked polymers of cellulose and chitosan pyrrolidone carboxylate, and derivatives of chitosan.

[0057] The binder content in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 9% by mass or less, and even more preferably 3% by mass or more and 8% by mass or less. The upper limit of the binder content may be 5% by mass, 4% by mass, or 3% by mass. By setting the binder content within the above range, the positive electrode active material can be stably maintained.

[0058] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose and methylcellulose. If the thickening agent has a functional group that reacts with lithium, etc., this functional group may be deactivated beforehand by methylation or the like. The thickening agent may also function as a binder. One or more types of thickening agents can be used. When the positive electrode active material layer contains a thickening agent, the content of the thickening agent in the positive electrode active material layer is preferably 0.1% by mass or more and 8% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the positive electrode active material layer does not contain a thickening agent.

[0059] The filler is not particularly limited. The filler is a component other than the positive electrode active material (polyanionic compounds containing iron elements and other positive electrode active materials), conductive agents, binders, and thickeners, and may be a component that is intentionally included. The filler may be included as a component that fills gaps in the positive electrode active material layer, or it may be included for other purposes. The filler may be an organic substance such as a polyolefin, or an inorganic substance such as an inorganic oxide, hydroxide, or carbonate. One or more types of fillers can be used. When the positive electrode active material layer contains a filler, the filler content in the positive electrode active material layer can be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the positive electrode active material layer does not contain a filler.

[0060] The positive electrode active material layer may further contain other components besides the positive electrode active material (polyanionic compounds containing iron elements and other positive electrode active materials), conductive agent, binder, thickener, and filler. These other components may include those unintentionally present in the positive electrode active material layer. Furthermore, the positive electrode active material layer may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these other components in the positive electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit of the content of unintentionally present components in the positive electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit for the amount of impurities unintentionally included in the positive electrode active material layer may be 10% by mass, or it may be 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass.

[0061] The average thickness of the positive electrode active material layer laminated on one side of the positive electrode substrate may be, for example, 1 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode active material layer may be 2 μm, 3 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm.

[0062] The upper limit of the average thickness of the positive electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, 40 μm, 20 μm, 15 μm, or 10 μm. The mass per unit area of ​​the positive electrode active material layer laminated on one side of the positive electrode substrate may be, for example, 4 mg / cm². ２ 100mg / cm or more ２ The following is also acceptable: The lower limit of the mass per unit area of ​​the positive electrode active material layer is 2 mg / cm². ２ 3 mg / cm ２ , 4 mg / cm ２ or 6 mg / cm ２ Preferably, 8 mg / cm ２ More preferably, 10 mg / cm² ２ This is even more preferable. The upper limit of the mass per unit area of ​​the positive electrode active material layer is 50 mg / cm². ２ , 20 mg / cm２ , 15 mg / cm ２ , 12 mg / cm ２ , 10 mg / cm ２ or 8 mg / cm ２ That's fine.

[0063] The porosity of the positive electrode active material layer may be, for example, 20% or more and 50% or less. The lower limit of the porosity of the positive electrode active material layer may be 25%, 30%, or 35%. The upper limit of the porosity of the positive electrode active material layer may be 45%, 40%, or 35%. The "porosity (%)" of the positive electrode active material layer and the negative electrode active material layer described later is calculated by taking the apparent volume (volume including voids) of the positive (negative) electrode active material layer as V １ Let V be the sum of the actual volumes of each material constituting the positive (negative) electrode active material layer. ２ In that case, (1-V ２ / V １ It is calculated using the formula ) × 100. The sum of the actual volumes of each material constituting the positive (negative) electrode active material layer V ２ This can be calculated from the content of each material in the positive (negative) electrode active material layer and the true density of each material.

[0064] On the surface of the positive electrode active material layer facing the positive electrode substrate, the ratio of the conductive agent to the total components in the positive electrode active material layer (hereinafter also simply referred to as "conductive agent ratio") is 30% or more. The lower limit of the conductive agent ratio is preferably 40%, more preferably 50%, even more preferably 60%, even more preferably 70%, and particularly preferably 75%. By having a conductive agent ratio above the above lower limit, the resistance of the non-aqueous electrolyte energy storage element can be reduced. The upper limit of the conductive agent ratio is 90%, and may also be 80%. By having a conductive agent ratio below the above upper limit, it can be kept within an appropriate range in the present invention, and an increase in manufacturing costs can be suppressed. From the viewpoint of facilitating high-density formation of the positive electrode active material layer, the upper limit of the conductive agent ratio may be 70%, 60%, or 50%. The proportion of the conductive agent can be adjusted by changing the stirring conditions of the positive electrode mixture paste when forming the positive electrode active material layer, changing the drying conditions of the positive electrode mixture paste, and, if the conductive agent is a carbon material, by adjusting the average length of the conductive agent and the functional groups it possesses.

[0065] (Method for Manufacturing a Positive Electrode) A positive electrode according to one embodiment of the present invention can be manufactured by known methods. The positive electrode can be manufactured, for example, by directly applying a paste-like positive electrode mixture (positive electrode mixture paste) to a positive electrode substrate and drying it to form a positive electrode active material layer. The positive electrode mixture paste usually contains positive electrode active material (polyanionic compounds containing iron elements and other positive electrode active materials), a conductive agent, other optional components, and a dispersion medium. From the viewpoint of increasing the density of the positive electrode active material layer, it is preferable to press the positive electrode mixture after drying.

[0066] In the manufacture of a positive electrode, it is preferable to apply the positive electrode mixture paste to the positive electrode substrate after stirring. For stirring conditions, using a disperser, which is a stirring device with high-speed rotating blades, or a film-film swirling stirring device such as the Filmix® manufactured by Primix Corporation, can improve the dispersibility of the conductive agent. Furthermore, when using a stirring device, the dispersion state of the positive electrode active material and conductive agent can be controlled by adjusting the stirring speed and stirring time. The lower limit of the stirring speed (peripheral speed) of the stirring device is preferably 3 m / sec, more preferably 6 m / sec, and even more preferably 10 m / sec. By setting the peripheral speed of the stirring device above the above lower limit, the positive electrode active material and conductive agent can be effectively dispersed. The upper limit of the peripheral speed of the stirring device is preferably 30 m / sec, more preferably 25 m / sec, and even more preferably 20 m / sec. By setting the peripheral speed of the stirring device below the above upper limit, aggregation of the positive electrode active material and conductive agent due to overdispersion can be suppressed.

[0067] <Non-aqueous electrolyte energy storage element> A non-aqueous electrolyte energy storage element according to one embodiment of the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte, and a container for housing them. The non-aqueous electrolyte energy storage element may further include a separator interposed between the positive electrode and the negative electrode to electrically insulate them. The positive electrode, the negative electrode, and any separator typically constitute an electrode body. At least a portion of the non-aqueous electrolyte is usually present in a state of being impregnated into the electrode body. The non-aqueous electrolyte energy storage element according to one embodiment of the present invention may further include other components.

[0068] For example, the non-aqueous electrolyte energy storage element 1 shown in Figure 1, according to one embodiment of the present invention, comprises an electrode body 2, a non-aqueous electrolyte (not shown), and a rectangular parallelepiped container 3 that houses them. The non-aqueous electrolyte energy storage element 1 in Figure 1 further comprises a positive electrode lead 4, a positive electrode external terminal 5, a negative electrode lead 6, and a negative electrode external terminal 7. The positive electrode lead 4 and the negative electrode lead 6 are housed together with the electrode body 2, etc., inside the container 3. The positive electrode external terminal 5 and the negative electrode external terminal 7 are provided outside the container 3. The positive electrode constituting the electrode body 2 is electrically connected to the positive electrode external terminal 5 via the positive electrode lead 4. The negative electrode constituting the electrode body 2 is electrically connected to the negative electrode external terminal 7 via the negative electrode lead 6.

[0069] The non-aqueous electrolyte energy storage element of the present invention may also be a non-aqueous electrolyte secondary battery. The following will describe in detail the main components constituting the non-aqueous electrolyte energy storage element according to one embodiment of the present invention, focusing on the case where the non-aqueous electrolyte energy storage element is a non-aqueous electrolyte secondary battery (particularly a lithium-ion secondary battery), but this is not intended to limit the scope of application of the present invention.

[0070] (Positive electrode) The positive electrode is a positive electrode for a non-aqueous electrolyte energy storage element according to the embodiment of the present invention described above.

[0071] (Negative electrode) The negative electrode comprises a negative electrode substrate and a negative electrode active material layer laminated directly to the negative electrode substrate or via an intermediate layer. Typically, the negative electrode has a portion where the negative electrode substrate is exposed. This exposed portion of the negative electrode substrate is usually connected to the negative electrode lead described above. The negative electrode may have a shape such as a sheet, plate, or strip.

[0072] The thickness of the negative electrode is set appropriately according to the application of the non-aqueous electrolyte energy storage element. The average thickness of the negative electrode may be, for example, 3 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode may be 4 μm, 5 μm, 10 μm, 20 μm, 30 μm, 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the negative electrode may be 500 μm, 400 μm, 300 μm, 250 μm, 200 μm, 150 μm, 100 μm, or 50 μm. The average thickness of the negative electrode is the average thickness of the portion in which the negative electrode active material layer is laminated directly to the negative electrode substrate or via an intermediate layer. If there are portions in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate and portions in which the negative electrode active material layer is laminated on only one side of the negative electrode substrate, then the average thickness of the portion in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate shall be used.

[0073] The negative electrode substrate is electrically conductive. Examples of materials for the negative electrode substrate include metals such as copper, nickel, titanium, iron, and their alloys (such as stainless steel), as well as carbon materials. Among these, copper or copper alloys are preferred.

[0074] The negative electrode substrate has a shape such as a sheet, plate, or strip. Examples of negative electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The negative electrode substrate may also be, for example, copper foil or copper alloy foil.

[0075] The average thickness of the negative electrode substrate may be, for example, 1 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 2 μm, 3 μm, 4 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the negative electrode substrate may be 30 μm, 20 μm, 15 μm, 10 μm, or 5 μm.

[0076] The intermediate layer is a layer placed between the negative electrode substrate and the negative electrode active material layer. The intermediate layer includes, for example, a conductive agent and a binder. When the intermediate layer includes a conductive agent, the contact resistance between the negative electrode substrate and the negative electrode active material layer can be reduced. Examples of conductive agents and binders used in the intermediate layer are the same as those used in the positive electrode active material layer described above.

[0077] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer optionally contains conductive agents, binders, thickeners, fillers, and other optional components. These optional components can be selected from the materials exemplified for the positive electrode. The negative electrode active material layer may be formed from a negative electrode mixture containing the negative electrode active material and other optional components. The negative electrode active material layer may be provided on only one side of a negative electrode substrate having a shape such as a sheet, or on both sides.

[0078] For the negative electrode active material, known negative electrode active materials can be used. For lithium-ion secondary batteries, materials that can intercept and release lithium ions are usually used as negative electrode active materials. Examples of negative electrode active materials include metallic lithium; metals or metalloids such as silicon and tin; metal oxides or metalloid oxides such as silicon oxide, titanium oxide, and tin oxide; Li ４ Ti ５ O １２ LiTio ２ TiNb ２ O ７ Examples include titanium-containing oxides; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitic carbon. Among these materials, carbon materials are preferred, and graphite or non-graphitic carbon is more preferred. Graphite may have its surface coated with other materials such as non-graphitic carbon. One or more types of negative electrode active materials can be used.

[0079] "Graphite" refers to the average lattice plane spacing (d) of the (002) plane, determined by X-ray diffraction before charging or discharging or during the discharge state. ００２ This refers to carbon materials with a n-scale of 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite.

[0080] "Non-graphite carbon" refers to the average lattice plane spacing (d) of the (002) plane, which is determined by X-ray diffraction before charging / discharging or during the discharge state. ００２ ) refers to carbon materials with a nautical index of 0.34 nm or more and 0.42 nm or less. Non-graphitic carbons include poorly graphitizable carbons and easily graphitizable carbons. "Poorly graphitizable carbon" refers to the above d ００２This refers to carbon materials with a nautical radius of 0.36 nm or more and 0.42 nm or less. "Easily graphitizable carbon" refers to the above d ００２ This refers to carbon materials with a nautical radius of 0.34 nm or more and less than 0.36 nm.

[0081] Here, the "discharge state" of the carbon material refers to a state in which the carbon material, which is the negative electrode active material, is discharged in such a way that charge transport ions such as lithium ions that can be intercepted and released during charging and discharging are sufficiently released. For example, in a half-cell using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic lithium as the counter electrode, this is a state in which the open-circuit voltage is 0.7V or higher.

[0082] The negative electrode active material may be in particulate form. The average particle size of the negative electrode active material can be, for example, 1 nm to 100 μm. If the negative electrode active material is a carbon material, titanium-containing oxide, or polyphosphate compound, its average particle size may be 1 μm to 100 μm. If the negative electrode active material is Si, Sn, Si oxide, or Sn oxide, its average particle size may be 1 nm to 15 μm, or 1 nm to 1 μm. Setting the average particle size of the negative electrode active material above the lower limit makes it easier to manufacture or handle. Setting the average particle size of the negative electrode active material below the upper limit improves the electronic conductivity of the negative electrode active material layer.

[0083] The content of the negative electrode active material in the negative electrode active material layer is preferably, for example, 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the negative electrode active material layer.

[0084] When the negative electrode active material is a metal such as metallic lithium, the negative electrode active material layer may be in the form of foil. The metallic lithium may exist as pure metallic lithium consisting substantially of the element lithium alone, or as a lithium alloy containing other metallic elements. When the negative electrode active material is a metal such as metallic lithium, the lithium element content in the negative electrode active material layer may be 90% by mass or more, 99% by mass or more, or 100% by mass.

[0085] When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. The content of the conductive agent in the negative electrode active material layer may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a conductive agent.

[0086] When the negative electrode active material layer contains a binder, the binder content in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The binder content in the negative electrode active material layer may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a binder.

[0087] When the negative electrode active material layer contains a thickening agent, the content of the thickening agent in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The content of the thickening agent in the negative electrode active material layer may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a thickening agent.

[0088] The filler in the negative electrode active material layer is a component other than the negative electrode active material, conductive agent, binder, and thickener, and may be a component that is intentionally included. The filler may be included as a component that fills gaps in the negative electrode active material layer, or it may be included for other purposes. When the negative electrode active material layer contains a filler, the filler content in the negative electrode active material layer can be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a filler.

[0089] The negative electrode active material layer may further contain other components besides the negative electrode active material, conductive agent, binder, thickener, and filler. These other components may include those unintentionally present in the negative electrode active material layer. Furthermore, the negative electrode active material layer may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these other components in the negative electrode active material layer may be 10% by mass, or 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of unintentionally present components in the negative electrode active material layer may be 10% by mass, or 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of unintentionally present impurities in the negative electrode active material layer may be 10% by mass, or 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0090] The thickness of the negative electrode active material layer is set appropriately according to the type of negative electrode active material, the application of the non-aqueous electrolyte energy storage element, etc. The average thickness of the negative electrode active material layer laminated on one side of the negative electrode substrate may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode active material layer may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of the negative electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​the negative electrode active material layer laminated on one side of the negative electrode substrate may be, for example, 2 mg / cm². ２ 50mg / cm or more ２ The following is also acceptable: The lower limit of the mass per unit area of ​​the negative electrode active material layer is 3 mg / cm². ２ , 4 mg / cm ２ 5 mg / cm ２ or 6 mg / cm ２ It may also be the case that the upper limit of the mass per unit area of ​​the negative electrode active material layer is 30 mg / cm². ２ , 20 mg / cm ２ , 15 mg / cm ２ , 12 mg / cm ２ or 10 mg / cm² ２ That's fine.

[0091] The porosity of the negative electrode active material layer may be, for example, 30% to 70%. The lower limit of the porosity of the negative electrode active material layer may be 35%, 40%, or 45%. The upper limit of the porosity of the negative electrode active material layer may be 60%, 50%, or 40%. In cases where the negative electrode active material layer is foil-like, the porosity of the negative electrode active material layer may be 0%.

[0092] (Method for Manufacturing the Negative Electrode) The negative electrode can be manufactured by known methods. The negative electrode can be manufactured, for example, in the same way as the method for manufacturing the positive electrode described above, by applying a paste-like negative electrode mixture (negative electrode mixture paste) directly to the negative electrode substrate or via an intermediate layer, and drying it to form a negative electrode active material layer. After drying, the negative electrode active material layer may be pressed or otherwise subjected to the process. If the negative electrode active material is a metal such as metallic lithium, it can also be manufactured by laminating metal foil directly to the negative electrode substrate or via an intermediate layer, and then pressing it (e.g., roll rolling).

[0093] (Separator) A known separator can be used. Examples of separators include a separator consisting only of a substrate layer, or a separator in which an inorganic layer containing inorganic particles and a binder is formed on one or both sides of the substrate layer.

[0094] Examples of the substrate layer form of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these forms, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of liquid retention of non-aqueous electrolytes. The material of the substrate layer of the separator is not particularly limited as long as it has insulating properties, but resins such as polyolefins (polyethylene, polypropylene, etc.), polyimide, and aramid are preferred.

[0095] Examples of inorganic compounds constituting the inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, and magnesium oxide; 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; mineral resource-derived materials such as talc, zeolite, kaolin, bentonite, and mica, or their artificial counterparts. One or more types of inorganic particles can be used. The average particle size of the inorganic particles is preferably, for example, 0.5 μm to 10 μm. The inorganic particle content in the inorganic layer is preferably 50% to 99% by mass, and more preferably 80% to 98% by mass.

[0096] Examples of binders used in the inorganic layer include those similar to those exemplified in the positive electrode active material layer.

[0097] The porosity of the separator may be, for example, 20% or more and 80% or less. The lower limit of the separator's porosity may be 30%, 40%, or 50% from the viewpoint of discharge performance, etc. The upper limit of the separator's porosity may be 70%, 60%, or 50% from the viewpoint of strength, etc. In this specification, "porosity" refers to a volume-based value and means a measurement value obtained using a mercury porosimeter.

[0098] The average thickness of the separator may be, for example, 10 μm or more and 40 μm or less, or 15 μm or more and 30 μm or less.

[0099] A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as a separator. A polymer gel may also be used in combination with a porous resin film, nonwoven fabric, etc., as described above, as a separator.

[0100] (Electrode Body) As the electrode body, known structures such as wound electrode bodies and laminated electrode bodies can be used.

[0101] A wound electrode has a structure in which the positive electrode and negative electrode are wound together while being insulated. The wound electrode may be cylindrical or flattened. The electrode 2 of the non-aqueous electrolyte energy storage element 1 in Figure 1 is a flattened wound electrode. A wound electrode can be manufactured, for example, by the following procedure. First, a laminate is obtained by stacking a positive electrode, a separator, and a negative electrode, each formed in a strip shape. A wound electrode is obtained by winding this laminate.

[0102] A laminated electrode body has a structure in which one or more positive electrodes and one or more negative electrodes are stacked in an insulated state. For example, a laminated electrode body can be obtained by stacking a positive electrode, a separator, and a negative electrode, each formed in a rectangular shape.

[0103] Other electrode structures can also be used, such as those in which at least one of the positive and negative electrodes is folded in a bellows-like manner and stacked.

[0104] (Non-aqueous electrolyte) Known non-aqueous electrolytes can be used as the non-aqueous electrolyte. A non-aqueous electrolyte is a medium that is responsible for transporting charge transport ions (e.g., lithium ions) between the positive electrode and the negative electrode, and which is substantially free of water. The water content in the non-aqueous electrolyte may be, for example, 10,000 ppm or less, 5,000 ppm or less, 1,000 ppm or less, 500 ppm or less, 100 ppm or less, preferably 50 ppm or less, and more preferably 20 ppm or less. Examples of non-aqueous electrolytes include non-aqueous electrolyte solutions and solid electrolytes. A non-aqueous electrolyte may be a combination of a non-aqueous electrolyte solution and a solid electrolyte, but one consisting of a non-aqueous electrolyte solution is preferred.

[0105] (Non-aqueous electrolyte) A non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0106] Any known non-aqueous solvent can be used. Examples of non-aqueous solvents include carbonates, esters, ethers, amides, and nitriles. Examples of carbonates include cyclic carbonates and linear carbonates. Examples of esters include carboxylic acid esters, phosphate esters, and sulfonic acid esters. As non-aqueous solvents, compounds in which some of the hydrogen atoms contained in these compounds are substituted with halogen atoms may also be used. One or more non-aqueous solvents can be used.

[0107] A cyclic carbonate is a carbonate having a ring structure containing a carbonate group (-O-C(=O)-O-). Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, styrene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. A cyclic carbonate may be a saturated cyclic carbonate such as ethylene carbonate, or an unsaturated cyclic carbonate such as vinylene carbonate. "Saturated" means not having carbon-carbon unsaturated bonds (carbon-carbon double bonds and carbon-carbon triple bonds). "Unsaturated" means having carbon-carbon unsaturated bonds. As the cyclic carbonate, saturated cyclic carbonates are preferred, and ethylene carbonates are more preferred.

[0108] A chain-like carbonate refers to a carbonate that does not have a ring structure containing a carbonate group. Examples of chain-like carbonates include diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. The chain-like carbonate may be a saturated chain-like carbonate such as dimethyl carbonate, or an unsaturated chain-like carbonate such as diphenyl carbonate. A saturated chain-like carbonate is preferred as the chain-like carbonate, and ethyl methyl carbonate is more preferred.

[0109] The non-aqueous solvent preferably contains carbonate, more preferably contains cyclic carbonate and chain carbonate. The content of carbonate in the non-aqueous solvent is preferably 80% by volume or more and 100% by volume or less, may be 99% by volume or more and 100% by volume, or may be 100% by volume. By using cyclic carbonate, the dissociation of the electrolyte salt can be promoted and the ionic conductivity of the non-aqueous electrolyte can be increased. By using chain carbonate, the viscosity of the non-aqueous electrolyte can be kept low. When cyclic carbonate and chain carbonate are used in combination, the volume ratio of cyclic carbonate to chain carbonate (cyclic carbonate: chain carbonate) is preferably, for example, in the range of 5:95 to 50:50.

[0110] The electrolyte salt refers to an ionic compound in which the cation is a charge-transporting ion and which is solid at room temperature (20°C) under 1 atm. Known electrolyte salts can be used as the electrolyte salt. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, etc. Among these, lithium salts are preferred. One or more kinds of electrolyte salts can be used.

[0111] Examples of the lithium salt include inorganic lithium salts such as LiPF ６ , LiPO ２ F ２ , LiBF ４ , LiClO ４ , etc., imide salts such as LiN(SO ２ F) ２ (LiFSI), LiN(SO ２ CF ３ ) ２ (LiTFSI), LiN(SO ２ C ２ F ５ ) ２ , LiN(SO ２ CF ３ )(SO ２ C ４ F ９ , etc., and LiB(C ２ O ４ ) ２ , LiBF ２ (C ２ O ４), LiPF ２ (C ２ O ４ ) ２ Examples include lithium oxalate salts such as LiN(SO4). ２ F) ２ This also applies to inorganic lithium salts. Among these, inorganic lithium salts and imide salts are preferred. LiPF is an example of an inorganic lithium salt. ６ This is preferable. As imide salts, LiFSI and LiTFSI are preferred, with LiFSI being more preferred. In some cases, it is also preferable to use an inorganic lithium salt and an imide salt in combination.

[0112] The electrolyte salt content in the non-aqueous electrolyte is 0.1 mol / dm³ at room temperature (20°C) at 1 atmosphere. ３ 2.5mol / dm or more ３ The following is preferred: 0.3 mol / dm ３ 2.0mol / dm or more ３ The following is more preferable: 0.5 mol / dm ３ More than 1.7mol / dm ３ The following is even more preferable: 0.7 mol / dm ３ 1.5mol / dm or more ３ The following is particularly preferable. By setting the electrolyte salt content within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0113] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and electrolyte salt. One or more types of additives may be used. When additives are used in the non-aqueous electrolyte, the additive content in the non-aqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, even more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less.

[0114] (Solid Electrolyte) The solid electrolyte can be selected from any material that has ionic conductivity, such as lithium, sodium, and calcium, and is solid at room temperature (20°C) at 1 atmosphere. Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, and polymer solid electrolytes. One or more types of solid electrolytes can be used.

[0115] (Container) The container houses the electrode body and non-aqueous electrolyte in its internal space. The container material can be a metal material such as aluminum or stainless steel, or a resin material, with metal materials being preferred from the viewpoint of strength, etc. A composite material of metal and resin materials can also be used.

[0116] The shape of the container is not particularly limited, but it can be cylindrical, rectangular (square), disc-shaped, etc. The container may also be in the form of a sheet or other shape formed from a metal-resin composite film.

[0117] (Shape and application of non-aqueous electrolyte energy storage element) The shape of the non-aqueous electrolyte energy storage element according to one embodiment of the present invention is not particularly limited. The non-aqueous electrolyte energy storage element may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin cell battery, a button cell battery, etc.

[0118] The applications of the non-aqueous electrolyte energy storage element according to one embodiment of the present invention are not particularly limited. The non-aqueous electrolyte energy storage element can be used, for example, as a power source for automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, as a power source for electronic devices such as personal computers and communication terminals, and as a power storage power source.

[0119] The non-aqueous electrolyte energy storage element of the present invention can be used individually or in combination. The non-aqueous electrolyte energy storage element may be used individually when the required output and voltage are small. On the other hand, when at least one of the required output and voltage is large, the non-aqueous electrolyte energy storage element may be used as part of an energy storage device combined with other non-aqueous electrolyte energy storage elements. In an energy storage device composed of multiple non-aqueous electrolyte energy storage elements, at least one of the non-aqueous electrolyte energy storage elements included in the energy storage device may be a non-aqueous electrolyte energy storage element according to one embodiment of the present invention. The energy storage device will be described in detail later.

[0120] In the non-aqueous electrolyte energy storage element according to one embodiment of the present invention, the container may be restrained to maintain a certain thickness, or it may not be restrained in such a way. Alternatively, the container may be restrained to have a certain load applied to it. When the container is restrained, expansion of the container due to charge-discharge cycles, etc., may be suppressed, and a decrease in charge-discharge performance may be suppressed. When the container is restrained, the electrode body inside the container may or may not have a load applied to it. For example, the non-aqueous electrolyte energy storage element or energy storage device may be provided with a restraining member that performs such restraint.

[0121] <Method for Manufacturing a Non-Aqueous Electrolyte Energy Storage Element> A non-aqueous electrolyte energy storage element according to one embodiment of the present invention can be manufactured by a known method. The method for manufacturing the non-aqueous electrolyte energy storage element includes, for example, preparing a positive electrode, preparing a negative electrode, preparing a non-aqueous electrolyte, and housing the positive electrode, negative electrode, and non-aqueous electrolyte in a container. The manufacturing method may also include preparing a separator, and manufacturing an electrode body using the positive electrode, negative electrode, and separator. Housing the positive electrode, negative electrode, and non-aqueous electrolyte in a container may be equivalent to housing the electrode body and non-aqueous electrolyte in a container.

[0122] Preparing the positive electrode may also mean manufacturing the positive electrode. The positive electrode can be manufactured by the method described above. Preparing the negative electrode may also mean manufacturing the negative electrode. The negative electrode can be manufactured by the method described above. Preparing the non-aqueous electrolyte may also mean preparing the non-aqueous electrolyte. The non-aqueous electrolyte can be prepared, for example, by dissolving an electrolyte salt in a non-aqueous solvent. The positive electrode, negative electrode, separator, non-aqueous electrolyte, etc., may be prepared by purchase or other means.

[0123] The electrode body (or positive and negative electrode) and the non-aqueous electrolyte can be housed in a container by known methods. If the non-aqueous electrolyte is a non-aqueous electrolyte solution, for example, the electrode body (or positive and negative electrode) can be housed in the container first, and then the non-aqueous electrolyte solution can be injected through an inlet provided in the container. The inlet is sealed after the non-aqueous electrolyte solution is injected. The method for manufacturing the non-aqueous electrolyte energy storage element may further include initial charging and discharging of the assembled uncharged / discharged energy storage element.

[0124] The non-aqueous electrolyte energy storage element according to one embodiment of the present invention may be manufactured by other methods. For example, if the non-aqueous electrolyte energy storage element according to one embodiment of the present invention is an all-solid-state battery, it may be manufactured by pressing the forming materials of the positive electrode, separator, and negative electrode individually or collectively.

[0125] <Energy Storage Device> An energy storage device according to one embodiment of the present invention comprises two or more energy storage elements and one or more non-aqueous electrolyte energy storage elements according to the above embodiment of the present invention (hereinafter referred to as the "second embodiment"). The energy storage device according to the second embodiment only needs to have the technology according to one embodiment of the present invention applied to at least one energy storage element included in the energy storage device, and may comprise one non-aqueous electrolyte energy storage element according to the above embodiment of the present invention and one or more energy storage elements not relating to the above embodiment of the present invention, or may comprise two or more non-aqueous electrolyte energy storage elements according to the above embodiment of the present invention.

[0126] The energy storage device 30 according to the second embodiment in Figure 2 comprises a plurality of energy storage units 20. Each energy storage unit 20 comprises a plurality of electrically connected non-aqueous electrolyte energy storage elements 1. The energy storage device 30 may also include busbars (not shown) for electrically connecting the plurality of non-aqueous electrolyte energy storage elements 1, busbars (not shown) for electrically connecting the plurality of energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may also include a condition monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte energy storage elements 1.

[0127] <Other Embodiments> The non-aqueous electrolyte energy storage element of the present invention is not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. Furthermore, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0128] In the above embodiment, a case in which a non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery was described, but the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, lithium-ion capacitors, and other capacitors.

[0129] In the above embodiment, an electrode body in which a separator is interposed between the positive electrode and the negative electrode was described, but the electrode body does not need to have a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other, with a non-conductive layer formed on the active material layer of either the positive electrode or the negative electrode. Thus, the positive electrode and the negative electrode may further have layers other than the base material, intermediate layer, and active material layer. Furthermore, the positive electrode and the negative electrode do not need to have a layered structure.

[0130] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0131] [Example 1] (Preparation of positive electrode) A positive electrode mixture paste was prepared using lithium iron phosphate (LFP) as the positive electrode active material, furnace black (FB) as the conductive agent, polyvinylidene fluoride (PVDF) as the binder, and N-methylpyrrolidone (NMP) as the dispersion medium. The mass ratio of LFP, FB, and PVDF was 93.5:4.0:2.5 in terms of solid content. As LFP, secondary particles with a carbon material coating on the surface were used, and the average particle size after the formation of the positive electrode active material layer (after roll pressing of the positive electrode mixture) described later was 1.4 μm. As the conductive agent, furnace black with an average length of less than 35 nm and having hydroxyl and carboxyl groups as functional groups was used.

[0132] The above positive electrode mixture paste was stirred with Filmix (registered trademark) manufactured by Primix Corporation, then directly coated onto the positive electrode substrate, dried to form the positive electrode mixture, and then roll-pressed to form the positive electrode active material layer, thereby obtaining the positive electrode of Example 1. The positive electrode substrate was an aluminum foil that was not roughened and did not have through holes. The peripheral speed for stirring the positive electrode mixture paste was 15 m / sec.

[0133] On the surface of the positive electrode active material layer facing the positive electrode substrate, the ratio of the conductive agent to the total components in the positive electrode active material layer (hereinafter also simply referred to as the "ratio of the conductive agent") was 43%.

[0134] (Preparation of the negative electrode) A negative electrode mixture paste was prepared by mixing graphite, the negative electrode active material; styrene-butadiene rubber (SBR), the binder; carboxymethylcellulose (CMC), the thickener; and water, the dispersion medium. The mass ratio of graphite, SBR, and CMC was 97.8:1.0:1.2 in terms of solid content. The negative electrode mixture paste was applied to copper foil, which was the negative electrode substrate, dried, and roll-pressed to form a negative electrode active material layer, thereby obtaining the negative electrode.

[0135] (Preparation of non-aqueous electrolyte) A non-aqueous solvent is prepared by mixing ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 20:35:45, and LiPF is added as the electrolyte salt. ６ 0.1 mol / dm ３ LiFSI at 0.8 mol / dm ３A non-aqueous electrolyte was obtained by mixing at the specified concentrations.

[0136] (Separator) A polyethylene microporous membrane was used as the separator.

[0137] (Assembly of Non-Aqueous Electrolyte Energy Storage Element) The positive electrode, negative electrode, and separator described above were stacked to create a wound electrode body. The maximum density of the positive electrode active material layer when creating the wound electrode body of Example 1 was 2.24 g / cm³. ３ This was the result. Here, "maximum density of the positive electrode active material layer" means the maximum density at which the positive electrode active material layer does not break when fabricating the wound electrode body. The obtained wound electrode body was placed in a container, then the non-aqueous electrolyte was poured into the container, and the container was sealed to obtain the non-aqueous electrolyte energy storage element of Example 1.

[0138] [Examples 2 to 4, Comparative Examples 1 to 3] Non-aqueous electrolyte energy storage elements of Examples 2 to 4 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1, except that the average particle size of the positive electrode active material after the formation of the positive electrode active material layer and the content of the conductive agent in the positive electrode active material layer were adjusted as shown in Table 1, and the content of the positive electrode active material was adjusted so that the total content of the positive electrode active material and conductive agent in the positive electrode active material layer was the same as in Example 1. The ratio of the presence of the conductive agent and the maximum density of the positive electrode active material layer are shown in Table 1. Note that the LFP used in Example 4 was a granulated product that had not been crushed beforehand. The average particle size of the LFP used in Example 4 before roll pressing was 4.9 μm, but since the fracture strength was 10.6 MPa, it was crushed during roll pressing, and the average particle size after the formation of the positive electrode active material layer (after roll pressing of the positive electrode mixture) became 1.7 μm.

[0139] [Comparative Example 4] A non-aqueous electrolyte energy storage element of Comparative Example 4 was obtained in the same manner as in Example 1, except that the type of conductive agent in the positive electrode was changed to acetylene black with an average length of approximately 35 nm and no functional groups, and the content of the conductive agent in the positive electrode was adjusted as shown in Table 1. The ratio of conductive agent and the maximum density of the positive electrode active material layer are shown in Table 1.

[0140] [Comparative Examples 5 and 6] A positive electrode mixture paste was prepared in the same manner as in Example 1, except that the content of the conductive agent in the positive electrode was adjusted as shown in Table 1.

[0141] The above cathode mixture paste was stirred using a rotation / revolution mixer manufactured by Thinky Co., Ltd. (registered trademark), then directly coated onto the cathode substrate, dried, and roll-pressed to form a cathode active material layer, thereby obtaining the cathodes of Comparative Examples 5 and 6. The cathode substrate used was the same as in Example 1. The stirring conditions for the cathode mixture paste were 3000 rpm, and the total stirring time was 8 minutes.

[0142] Subsequently, the negative electrode was fabricated, the non-aqueous electrolyte was prepared, and the non-aqueous electrolyte energy storage element was assembled in the same manner as in Example 1 to obtain the non-aqueous electrolyte energy storage elements of Comparative Examples 5 and 6. The ratio of conductive agent and the maximum density of the positive electrode active material layer are shown in Table 1.

[0143] [Evaluation] (Initial Charge / Discharge) Initial charge and discharge were performed on each non-aqueous electrolyte energy storage element in the examples and comparative examples under the following conditions. Constant current charging was performed in a constant temperature bath at 25°C with a charging current of 1.0C and a charging termination voltage of 3.50V, followed by constant voltage charging at 3.50V. The charging termination condition was defined as when the charging current decreased to 0.01C. A 10-minute rest period was then observed. Constant current discharge was performed with a discharge current of 1.0C and a discharge termination voltage of 2.00V.

[0144] (Initial DC Resistance) Next, each non-aqueous electrolyte energy storage element was charged with a constant current of 1.0C at a temperature of 25°C to adjust the state of charge (SOC) to 50%. After being stored in a -10°C constant temperature bath for 4 hours, the non-aqueous electrolyte energy storage elements were discharged for 60 seconds each at a constant current of 0.1C, 0.2C, or 0.3C while maintaining the -10°C temperature environment. After each discharge, constant current charging was performed with a current of 0.2C to adjust the SOC to 50%. The relationship between the current in each discharge and the voltage 10 seconds after the start of discharge was plotted, and the initial DC resistance (initial DCR) was determined from the slope of the straight line obtained from the three plots. The initial DCR is shown in Table 1.

[0145]

[0146] As shown in Table 1, in Comparative Example 1, where the average particle size of the polyanion compound is greater than 2.5 μm, the maximum density of the positive electrode active material layer was 2.20 g / cm³. ３The density of the positive electrode active material layer was less than 30%, making it difficult to increase the density. In addition, in Comparative Examples 2 to 6, where the proportion of conductive agent was less than 30%, the initial DCR was greater than 3.50 Ω, indicating high resistance. In contrast, in Examples 1 to 4, where the average particle size of the polyanion compound was 2.5 μm or less and the proportion of conductive agent was 30% or more, the maximum density of the positive electrode active material layer was 2.20 g / cm³. ３ Furthermore, the initial DCR was 3.50Ω or less, indicating low resistance.

[0147] This invention can be applied to non-aqueous electrolyte energy storage elements used as power sources for electronic devices such as personal computers and communication terminals, as well as for automobiles and industrial applications.

[0148] 1. Non-aqueous electrolyte energy storage element 2. Electrode body 3. Container 4. Positive electrode lead 5. Positive electrode external terminal 6. Negative electrode lead 7. Negative electrode external terminal 20. Energy storage unit 30. Energy storage device

Claims

1. A positive electrode for a non-aqueous electrolyte energy storage element, comprising a positive electrode substrate and a positive electrode active material layer directly laminated on the positive electrode substrate, wherein the positive electrode active material layer contains a polyanionic compound containing an iron element and a conductive agent, the average particle size of the polyanionic compound is 2.5 μm or less, and the ratio of the conductive agent to the total components in the positive electrode active material layer on the surface of the positive electrode active material layer facing the positive electrode substrate is 30% to 90%.

2. The positive electrode for a non-aqueous electrolyte energy storage element according to claim 1, wherein the positive electrode substrate is a non-roughened substrate.

3. The positive electrode for a non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the content of the conductive agent in the positive electrode active material layer is 10.0% by mass or less.

4. A non-aqueous electrolyte energy storage element comprising a positive electrode for a non-aqueous electrolyte energy storage element according to claim 1 or claim 2.

5. An energy storage device comprising two or more energy storage elements, and one or more non-aqueous electrolyte energy storage elements as described in claim 4.

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