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

Abstract

The present invention provides a positive electrode for a non-aqueous electrolyte energy storage element that uses a polyanion compound containing an iron element, which can reduce the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures and suppress the increase in resistance after charge-discharge cycles, and a non-aqueous electrolyte energy storage element equipped with such a positive electrode. [Solution] A positive electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a positive electrode active material layer containing a polyanionic compound containing an iron element and a conductive agent, wherein the log differential pore volume distribution curve of the positive electrode active material layer has a first peak in the range of pore diameter 0.04 μm or less, a second peak in the range of pore diameter 0.1 μm or more and 1 μm or less, and the log differential pore volume at the second peak is 0.18 cm³. 3 The amount is less than or equal to / g, and the content of the conductive agent in the positive electrode active material layer is greater than 2.0% by mass.

Description

Technical Field

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

Background Art

[0002] Non-aqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, and automobiles because of their high energy density. A non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and is configured to charge and discharge by transferring charge-transporting ions between both electrodes. In addition, as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely popular.

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Polyanion compounds containing iron elements such as lithium iron phosphate have advantages such as being relatively inexpensive compared to lithium transition metal composite oxides. On the other hand, in non-aqueous electrolyte storage elements using such polyanion compounds as positive electrode active materials, it is desired to reduce the initial resistance at low temperatures of the non-aqueous electrolyte storage element and to suppress the increase in resistance after charge-discharge cycles.

[0006] 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, can reduce the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures, and can suppress the increase in resistance after a charge-discharge cycle, and a non-aqueous electrolyte energy storage element equipped with such a positive electrode for a non-aqueous electrolyte energy storage element. [Means for solving the problem]

[0007] A positive electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a positive electrode active material layer containing a polyanionic compound containing an iron element and a conductive agent, wherein the log differential pore volume distribution curve of the positive electrode active material layer has a first peak in the range of pore diameter 0.04 μm or less, a second peak in the range of pore diameter 0.1 μm or more and 1 μm or less, and the log differential pore volume at the second peak is 0.18 cm³. 3 The amount is less than or equal to / g, and the content of the conductive agent in the positive electrode active material layer is greater than 2.0% by mass.

[0008] 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. [Effects of the Invention]

[0009] 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, can reduce the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures, and can suppress the increase in resistance after a charge-discharge cycle, and a non-aqueous electrolyte energy storage element equipped with such a positive electrode for a non-aqueous electrolyte energy storage element is provided. [Brief explanation of the drawing]

[0010] [Figure 1] 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] Figure 2 is a schematic diagram showing an energy storage device comprising a non-aqueous electrolyte energy storage element according to multiple embodiments of the present invention. [Figure 3]Figure 3 shows the log differential pore volume distribution curve of the positive electrode active material layer of the positive electrode for the non-aqueous electrolyte energy storage element of Example 1. [Modes for carrying out the invention]

[0011] 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.

[0012] [1] A positive electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a positive electrode active material layer comprising a polyanionic compound containing an iron element and a conductive agent, wherein the log differential pore volume distribution curve of the positive electrode active material layer has a first peak in the range of pore diameter 0.04 μm or less, a second peak in the range of pore diameter 0.1 μm or more and 1 μm or less, and the log differential pore volume at the second peak is 0.18 cm³. 3 The amount is less than or equal to / g, and the content of the conductive agent in the positive electrode active material layer is greater than 2.0% by mass.

[0013] The positive electrode for the non-aqueous electrolyte energy storage element described in [1] above uses a polyanionic compound containing iron, which can reduce the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures and suppress the increase in resistance after the charge-discharge cycle. The reason for this is not clear, but the following reasons are speculated. In the positive electrode for a non-aqueous electrolyte energy storage element described in [1] above, the content of the conductive agent in the positive electrode active material layer is more than 2.0% by mass, so that conductive paths can be sufficiently formed in the positive electrode active material layer. Furthermore, the positive electrode active material layer of the positive electrode for the non-aqueous electrolyte energy storage element described in [1] above has a first peak in the log differential pore volume distribution curve, which is due to voids between primary particles of the iron-containing polyanion compound in the range of pore diameter 0.04 μm or less. The presence of a first peak in the positive electrode active material layer means that pores of an appropriate size are formed between the primary particles of the iron-containing polyanion compound to promote the penetration of the non-aqueous electrolyte. Sufficient penetration of the non-aqueous electrolyte between the primary particles of the iron-containing polyanion compound can improve the diffusivity of charge transport ions in the positive electrode active material layer. Furthermore, the positive electrode active material layer of the positive electrode for the non-aqueous electrolyte energy storage element described in [1] above has a second peak in the log differential pore volume distribution curve, which is caused by voids between secondary particles of the polyanionic compound containing iron in the range of pore diameters from 0.1 μm to 1 μm. The log differential pore volume at the second peak is 0.18 cm³. 3 A value of less than / g means that there are few voids between the secondary particles of the polyanionic compound containing iron. When there are few voids between the secondary particles of the polyanionic compound containing iron, it becomes easier to secure a contact area between the positive electrode substrate and the positive electrode active material layer, and an increase in contact resistance between the positive electrode substrate and the positive electrode active material layer can be suppressed. Furthermore, by uniformly dispersing the conductive agent in the positive electrode active material layer so as to fill the voids between the secondary particles of the polyanionic compound containing iron, the voids between the secondary particles of the polyanionic compound containing iron are reduced, and conductive paths in the positive electrode active material layer can be sufficiently formed. Therefore, the positive electrode for the non-aqueous electrolyte energy storage element described in [1] above has a conductive agent content of more than 2.0% by mass in the positive electrode active material layer, the log differential pore volume distribution curve of the positive electrode active material layer has a first peak and a second peak, and the log differential pore volume at the second peak is 0.18 cm³. 3 Combined with the fact that the value is less than / g, it is presumed that this will reduce the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures and suppress the increase in resistance after the charge-discharge cycle.

[0014] The pore volume distribution of the positive electrode active material layer is determined by the following procedure. 0.4 g of the positive electrode active material sample is placed in a sample tube and vacuum-dried at 120°C for 12 hours to thoroughly remove moisture from the sample. Next, the adsorption-side isotherms from 5 nm to 20 μm are measured using the mercury intrusion method, and the pore volume distribution is determined by calculation using the BJH method.

[0015] The sample for measuring the positive electrode active material layer is taken from the positive electrode for the non-aqueous electrolyte energy storage element (hereinafter also simply referred to as "positive electrode") before it is incorporated into the non-aqueous electrolyte energy storage element, or, in the case of a positive electrode incorporated into a non-aqueous electrolyte energy storage element, it is taken from a sample processed according to the following procedure. First, the non-aqueous electrolyte energy storage element is charged with a constant current of 0.05C until it reaches the charge termination voltage for normal use, bringing it to a fully charged state. After a 30-minute rest, it is discharged with a constant current of 0.05C until it reaches the discharge termination voltage for normal use. Note that "normal use" refers to using the non-aqueous electrolyte energy storage element under the charge and discharge conditions recommended or specified for the element, and if equipment for using the non-aqueous electrolyte energy storage element is available, it refers to using that equipment. The 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 here. For the test battery, with a current of 10mA per gram of positive electrode active material, the positive electrode potential is 2.0V (vs.Li / Li + Constant current discharge is performed until the positive electrode is fully discharged. The device is then disassembled again, and the positive electrode is removed. The removed positive electrode is washed with dimethyl carbonate. The disassembly of the non-aqueous electrolyte energy storage element and the washing with dimethyl carbonate are performed in an argon atmosphere with a dew point of -60°C or lower. Subsequently, a sample of the positive electrode active material layer is taken from the positive electrode before charging or discharging, or from the positive electrode removed from the non-aqueous electrolyte energy storage element, by peeling off the positive electrode substrate or similar method.

[0016] [2] The positive electrode for a non-aqueous electrolyte energy storage element described in [1] above comprises a positive electrode substrate and a positive electrode active material layer laminated on the positive electrode substrate, wherein the positive electrode substrate may be made of aluminum.

[0017] The positive electrode active material layer is usually formed by applying a positive electrode mixture to a positive electrode substrate and then pressing it. It is believed that the adhesion between the positive electrode substrate and the positive electrode active material layer is increased when the positive electrode mixture is pressed. In the positive electrode for a non-aqueous electrolyte energy storage element described in [2] above, the fact that the positive electrode substrate is made of aluminum makes it easy to increase the adhesion between the positive electrode substrate and the positive electrode active material layer. In other words, the contact resistance between the positive electrode substrate and the positive electrode active material layer is easily reduced, which can further reduce the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures and further suppress the increase in resistance after the charge-discharge cycle.

[0018] [3] In the positive electrode for a non-aqueous electrolyte energy storage element described in [2] above, the fracture strength of the polyanion compound may be 40 MPa or more.

[0019] In the positive electrode for a non-aqueous electrolyte energy storage element described in [3] above, the fracture strength of the polyanion compound is 40 MPa or more, so the polyanion compound has sufficient hardness. Therefore, when pressing the positive electrode mixture, the polyanion compound is less likely to deform and can easily be embedded in the positive electrode substrate, thereby improving the adhesion between the positive electrode substrate and the positive electrode active material layer. In other words, the positive electrode for a non-aqueous electrolyte energy storage element described in [3] above has reduced contact resistance between the positive electrode substrate and the positive electrode active material layer, which can further reduce the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures and further suppress the increase in resistance after the charge-discharge cycle.

[0020] "Breaking strength" is measured in accordance with JIS-Z-8844 (2019). The breaking strength is measured on the polyanion compound particles extracted from the positive electrode before it is incorporated into a non-aqueous electrolyte energy storage element, or from a positive electrode incorporated into a non-aqueous electrolyte energy storage element, which has been processed according to the procedure described above for measuring the pore volume distribution. 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. After that, it is washed with water and dried under reduced pressure at room temperature for 24 hours to obtain the polyanion compound particles. The work from peeling off the positive electrode active material layer to obtaining the polyanion compound particles is performed in an argon atmosphere with a dew point of -60°C or lower. The breaking strength is measured by taking five of the polyanion compound particles and adopting the average value.

[0021] [4] In the positive electrode for a non-aqueous electrolyte energy storage element described in any of [1] to [3] above, the log differential pore volume at the first peak is 0.2 cm³. 3 It may be more than / g.

[0022] In the positive electrode for a non-aqueous electrolyte energy storage element described in [4] above, the log differential pore volume at the first peak is 0.2 cm³. 3 Since the concentration is greater than or equal to / g, it is considered that adequately sized pores are formed between the primary particles of the polyanion compound to promote the penetration of the non-aqueous electrolyte. For this reason, the positive electrode for the non-aqueous electrolyte energy storage element described in [4] above can further reduce the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures and further suppress the increase in resistance after the charge-discharge cycle.

[0023] [5] 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 [4] above.

[0024] The non-aqueous electrolyte energy storage element described in [5] above includes a positive electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention, and uses a polyanionic compound containing an iron element, which has low initial resistance at low temperatures and can suppress resistance increase after charge-discharge cycles.

[0025] A positive electrode for a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte energy storage element, a method for manufacturing a non-aqueous electrolyte energy storage element, an energy storage device, and other embodiments according to one embodiment of the present invention will be described in detail below. Note that the lower and upper limits of each numerical range described in the embodiments of the present invention can be combined in any way.

[0026] <Positive electrode for non-aqueous electrolyte energy storage elements> A positive electrode (positive electrode) for a non-aqueous electrolyte energy storage element according to one embodiment of the present invention typically comprises a positive electrode substrate and a positive electrode active material layer laminated directly to the positive electrode substrate or via an intermediate layer. 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. From the viewpoint of particularly highlighting the effect of the present invention, which is to reduce the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures, it is preferable that the positive electrode active material layer is laminated directly to the positive electrode substrate.

[0027] 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, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode may be 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, or 100 μm. The average thickness of the positive electrode is the average thickness of the portion in which the positive electrode active material layer is laminated directly onto the positive electrode substrate or via an intermediate layer. If both portions exist in which the positive electrode active material layer is laminated on both sides of the positive electrode substrate and portions in 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 in which the positive electrode active material layer is laminated on both sides of the positive electrode substrate shall be used. Furthermore, in this specification, "average thickness" means the average value of the thickness measured at any five locations.

[0028] The positive electrode substrate is conductive. In this specification, "conductive" means that the volume resistivity is 10 -2It means that it is below Ω·cm. The volume resistivity shall be the value measured in accordance with JIS-H-0505 (1975). On the other hand, in this specification, "having no conductivity" or "(electrically) insulating" means that the above volume resistivity is 10 7 Ω·cm or more.

[0029] The positive electrode substrate is preferably made of aluminum. That the positive electrode substrate is made of aluminum means that the material of the positive electrode substrate is pure aluminum or an aluminum alloy. By making the positive electrode substrate made of aluminum, the adhesion between the positive electrode substrate and the positive electrode active material layer can be easily increased. Also, the potential resistance and electron conductivity can be enhanced, and the cost can be reduced. Examples of pure aluminum or aluminum alloys include A1085, A3003, A1N30, etc. defined in JIS-H-4000 (2014) or JIS-H-4160 (2006). Examples of other materials for the positive electrode substrate also include metals such as titanium, iron, and their alloys (such as stainless steel).

[0030] The positive electrode substrate has a shape such as a sheet shape, a plate shape, or a strip shape, for example. Examples of the form of the positive electrode substrate include a foil, a vapor deposition film, a mesh, a porous material, etc., and a foil is preferred. The positive electrode substrate may be, for example, a substrate made of a member other than aluminum provided with an aluminum layer by vapor deposition or the like, but it is preferably an aluminum foil. That is, the positive electrode substrate is preferably a pure aluminum foil or an aluminum alloy foil.

[0031] The positive electrode substrate is preferably a non-roughened substrate. By making the positive electrode substrate a non-roughened substrate, the effect of the present invention of reducing the initial resistance at low temperatures of the non-aqueous electrolyte storage element can be particularly significantly obtained. The non-roughened substrate means that 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 means the average value of the values measured at any five locations in accordance with JIS-B-0601 (2013).

[0032] 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 initial resistance of the non-aqueous electrolyte energy storage element at low temperatures, can be obtained particularly significantly.

[0033] The average thickness of the positive electrode substrate may be, for example, 3 μm or more and 50 μm or less. The lower limit of the average thickness of the positive electrode substrate may be 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, or 15 μm.

[0034] The intermediate layer is a layer placed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer includes, for example, a conductive agent and a binder. When the intermediate layer contains a conductive agent, the contact resistance between the positive electrode substrate and the positive 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, which will be described later.

[0035] The positive electrode active material layer contains a polyanionic compound containing iron and a conductive agent. The positive electrode active material layer may optionally contain other components such as a binder, thickener, and filler. The positive electrode active material layer may be formed from a positive electrode mixture containing a polyanionic compound containing iron, a conductive agent, and other optional components. The positive electrode active material layer may be provided on only one side of a positive electrode substrate having a shape such as a sheet, or on both sides.

[0036] 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 (i.e., 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, PO4 3- , SO4 2- , SiO4 4- , BO3 3- , VO4 3- etc. may be mentioned, and PO4 3- (phosphate anion) is preferable. The polyanion compound containing iron element may further contain a halogen element or the like.

[0037] The polyanion compound containing iron element is preferably represented by the following formula (1). Li a M b (AO c ) d X e ···(1) In formula (1), M is one or more transition metal elements containing at least iron element (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 may be decimals.

[0038] It is preferable that the content of Fe with respect to the content of M in formula (1) is 50 mol% or more, and more preferably 70 mol% or more, 90 mol% or more, or 99 mol% or more. As A, P is preferable. As X, F is preferable. In one embodiment, a = 1, b = 1, c = 4, d = 1, and e = 0 may be preferable in some cases.

[0039] Specific examples of polyanionic compounds containing iron include, for example, LiFePO4 and LiFe x Co 1-x PO4(0 <x<1)、LiFe x Mn 1-x PO4(0 <x<1)、LiFeVO4、Li2FeSiO4、Li2Fe2(SO4)3、LiFeBO3、LiFePO 3.9 F 0.2 Examples include the above. The atoms or polyanions in these compounds may be partially substituted with other atoms or anion species. Lithium iron phosphate (LiFePO4) is preferred as a polyanion compound containing iron. In lithium iron phosphate, some of the atoms or polyanions constituting lithium iron phosphate may be substituted with other atoms or anion species. A single polyanion compound containing iron may be used, or two or more may be used in mixture form.

[0040] 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 Pnma. A crystal structure that can be assigned to the space group Pnma means that in the X-ray diffraction pattern, it has a diffraction pattern that can be assigned to the space group Pnma.

[0041] 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. By coating the surface of the iron-containing polyanionic compound particles with a carbon material, good electronic conductivity can be achieved.

[0042] 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.

[0043] The lower limit of the average particle size of the iron-containing polyanion compound is preferably 0.5 μm, more preferably 1 μm, even more preferably 3 μm, even more preferably 5 μm, and may also be 8 μm. Setting the average particle size of the iron-containing polyanion compound to be above the above lower limit facilitates the manufacture or handling of the iron-containing polyanion compound. It also facilitates reducing the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures. The upper limit of the average particle size of the iron-containing polyanion compound is preferably 20 μm, more preferably 15 μm, even more preferably 12 μm, and may also be 10 μm. Setting the average particle size of the iron-containing polyanion compound to be below the above upper limit improves the electronic conductivity of the positive electrode active material layer. 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 using, for example, a pulverizer or classifier can be used to obtain particles of a predetermined particle size.

[0044] The lower limit of the fracture strength of the iron-containing polyanion compound is preferably 40 MPa, more preferably 45 MPa, and even more preferably 50 MPa. When the fracture strength of the iron-containing polyanion compound is above the above lower limit, the iron-containing polyanion compound is more likely to penetrate the positive electrode substrate, and the contact resistance between the positive electrode substrate and the positive electrode active material layer is easily reduced. The upper limit of the fracture strength of the iron-containing polyanion compound may be 100 MPa, 80 MPa, or 60 MPa. The fracture strength of the iron-containing polyanion compound can be controlled by the composition of the iron-containing polyanion compound and the type of carbon material coating its surface, as well as by the synthesis method of the iron-containing polyanion compound (hydrothermal method, solid-phase method, etc.) and manufacturing conditions such as firing conditions.

[0045] The positive electrode active material layer may contain other positive electrode active materials besides 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 the positive electrode active material.

[0046] The content of the iron-containing polyanion compound in the positive electrode active material layer is preferably 70% to 97% by mass, more preferably 80% to 96% by mass, and even more preferably 85% to 95% by mass. By setting the content of the iron-containing polyanion compound within the above range, it is possible to achieve both high energy density and manufacturability in the positive electrode active material layer.

[0047] 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 97% by mass, more preferably 80% to 96% by mass, and even more preferably 85% to 95% by mass. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the positive electrode active material layer.

[0048] Conductive agents are typically components made of conductive materials. Even if the volume resistivity of a conductive agent cannot be directly measured, if the volume resistivity is 10 -2 Materials 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 materials can take the form of powder or fibers. One or more conductive materials can be used. These materials may also be used in composite form as conductive materials. For example, a composite material of carbon black and CNTs may be used.

[0049] The content of the conductive agent in the positive electrode active material layer is greater than 2.0% by mass. The lower limit of the content of the conductive agent in the positive electrode active material layer is preferably 2.5% by mass, more preferably 3.0% by mass, and may be 3.5% by mass or 4.0% by mass. By having a content of the conductive agent in the positive electrode active material layer that is above the above lower limit, conductive paths are sufficiently formed in the positive electrode active material layer, which can reduce the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures and suppress the increase in resistance after the charge-discharge cycle. The upper limit of the content of the conductive agent in the positive electrode active material layer is preferably 8.0% by mass, and may be 7.0% by mass, 6.0% by mass, 5.0% by mass, or 4.5% by mass, from the viewpoint of ensuring the content of polyanionic compounds containing iron elements and increasing energy density.

[0050] Examples of binders include water-based binders and organic solvent-based binders.

[0051] A water-based binder is a binder that dissolves or disperses in water. A water-based binder may be one that dissolves or disperses in 100 parts by mass or more per 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 (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.

[0052] 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.

[0053] The binder may be a fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), a polyolefin (polyethylene, polypropylene, etc.), an elastomer (ethylene propylene diene rubber, styrene butadiene rubber, fluororubber, etc.), a polysaccharide polymer (cellulose, chitosan derivatives, etc.), etc. One or more types of binders may be used.

[0054] The binder content in the positive electrode active material layer is preferably 0.5% by mass or more and 8% by mass or less, more preferably 1% by mass or more and 6% by mass or less, and even more preferably 2% by mass or more and 5% by mass or less. The upper limit of the binder content may be 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.

[0055] 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.

[0056] The filler is not particularly limited. The filler is a component other than the positive electrode active material (polyanionic compound containing iron and other positive electrode active materials), 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 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.

[0057] 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 unintentionally included impurities 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.

[0058] The average thickness of one positive electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one positive electrode active material layer may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm.

[0059] The upper limit of the average thickness of one positive 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 ​​one positive electrode active material layer may be, for example, 4 mg / cm². 2 More than 100mg / cm 2 The following is also acceptable: The lower limit of the mass per unit area of ​​one positive electrode active material layer is 6 mg / cm². 2 Preferably, 8 mg / cm³ 2 More preferably, 10 mg / cm³ 2 This is even more preferable. The upper limit of the mass per unit area of ​​one positive electrode active material layer is 50 mg / cm². 2 , 20 mg / cm³ 2 , 15 mg / cm³ 2 , 12 mg / cm³ 2 or 10 mg / cm³ 2 That's fine.

[0060] 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 using the formula (1-V2 / V1)×100, where V1 is the apparent volume (volume including voids) of the positive (negative) electrode active material layer and V2 is the sum of the actual volumes of each material constituting the positive (negative) electrode active material layer. The sum of the actual volumes V2 of each material constituting the positive (negative) electrode active material layer can be calculated from the content of each material in the positive (negative) electrode active material layer and the true density of each material.

[0061] The log differential pore volume distribution curve of the positive electrode active material layer has a first peak in the range of pore diameters of 0.04 μm or less. The range of pore diameters in which the first peak exists is preferably 0.010 μm to 0.035 μm, more preferably 0.015 μm to 0.030 μm, and even more preferably 0.020 μm to 0.030 μm. By having the pore diameter in which the first peak exists within the above range, the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures can be reduced, and the increase in resistance after the charge-discharge cycle can be suppressed. The range of pore diameters in which the first peak exists can be adjusted by the synthesis method (hydrothermal method, solid-phase method, etc.) and synthesis conditions of the polyanion compound containing iron, the firing temperature, the type of carbon material coated on the surface of the particles of the polyanion compound containing iron, etc. In some cases, the range of pore diameters in which the first peak exists can be easily adjusted by adopting a solid-phase method as the synthesis method for the polyanion compound containing iron.

[0062] The lower limit of the log differential pore volume at the first peak is 0.2 cm. 3 / g is preferred, and 0.22cm 3 / g is more preferable, 0.25cm 3 / g is even more preferable. Having the log differential pore volume at the first peak be above the above lower limit allows for a further reduction in the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures. The upper limit of the log differential pore volume at the first peak is 1.0 cm. 3It may also be / g, 0.8cm 3 / g, 0.6cm 3 / g, 0.4cm 3 / g or 0.3cm 3 It may also be / g. The log differential pore volume at the first peak can be adjusted by the synthesis method (hydrothermal method, solid-phase method, etc.) and synthesis conditions of the iron-containing polyanionic compound, the calcination temperature, the type and amount of carbon material coated on the surface of the iron-containing polyanionic compound particles. The log differential pore volume at the first peak can sometimes be easily adjusted by adopting a solid-phase method as the synthesis method for the iron-containing polyanionic compound.

[0063] The log differential pore volume distribution curve of the positive electrode active material layer has a second peak in the range of pore diameters from 0.1 μm to 1 μm. The range of pore diameters in which the second peak exists is preferably 0.20 μm to 0.80 μm, more preferably 0.25 μm to 0.75 μm, and even more preferably 0.30 μm to 0.60 μm. By having the pore diameter in which the second peak exists within the above range, the initial resistance of the non-aqueous electrolyte energy storage element at low temperatures can be reduced, and the increase in resistance after the charge-discharge cycle can be suppressed. The range of pore diameters in which the second peak exists can be adjusted by the average particle size of the polyanionic compound containing iron, the pressing conditions (pressure, temperature, etc.) when forming the positive electrode active material layer, and the content and type of conductive agent contained in the positive electrode mixture.

[0064] The upper limit of the log differential pore volume at the second peak is 0.18 cm³. 3 It is / g and 0.17cm 3 / g, 0.15cm 3 / g or 0.10cm 3 It may also be / g. By keeping the log differential pore volume at the second peak below the above upper limit, the resistance increase after charge-discharge cycles of the non-aqueous electrolyte energy storage element can be further suppressed. The lower limit of the log differential pore volume at the second peak is 0.01 cm³. 3 It may also be / g, 0.05cm 3 / g, 0.08cm 3 / g or 0.10cm 3It may also be / g. The log differential pore volume at the second peak can be adjusted by the average particle size of the polyanionic compound containing iron, the pressing conditions (pressure, temperature, etc.) when forming the positive electrode active material layer, the content and type of conductive agent contained in the positive electrode mixture, the mixing conditions of the positive electrode mixture paste, etc.

[0065] The log differential pore volume at the first peak is preferably larger than the log differential pore volume at the second peak. The ratio of the log differential pore volume at the first peak to the log differential pore volume at the second peak is preferably 1.1 to 2.0, more preferably 1.2 to 1.9, and even more preferably 1.3 to 1.8.

[0066] The lower limit of the density of the positive electrode active material layer is 1.98 g / cm³, from the perspective of increasing energy density. 3 Preferably, 2.00 g / cm³ 3 More preferably, 2.05 g / cm³ 3 This is even more preferable. The upper limit of the density of the positive electrode active material layer is 2.50 g / cm³. 3 It may also be 2.30 g / cm³. 3 It may also be 2.20 g / cm³. 3 This may also be the case. The density of the positive electrode active material layer can be adjusted by the average particle size of the polyanionic compound containing iron, the pressing conditions (pressure, temperature, etc.) when forming the positive electrode active material layer, the drying conditions of the positive electrode mixture paste, etc.

[0067] (Method of manufacturing the positive electrode) The positive electrode can be manufactured by known methods. For example, the positive electrode can be manufactured by applying a paste-like positive electrode mixture (positive electrode mixture paste) directly to a positive electrode substrate or via an intermediate layer, and then drying it to form a positive electrode active material layer. The positive electrode mixture paste typically 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. After drying, the positive electrode active material layer may be subjected to pressing or other similar processes.

[0068] <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 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 typically present in a state of permeation into the electrode body. The non-aqueous electrolyte energy storage element according to one embodiment of the present invention may further include other components.

[0069] 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.

[0070] The non-aqueous electrolyte energy storage element of the present invention may also be a non-aqueous electrolyte secondary battery. Below, the main components constituting the non-aqueous electrolyte energy storage element according to one embodiment of the present invention will be described in detail, 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.

[0071] (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.

[0072] (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.

[0073] 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, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode may be 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, 200 μm, or 100 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.

[0074] The negative electrode substrate is electrically conductive. Examples of materials for the negative electrode substrate include metals such as copper, nickel, iron, and their alloys (such as stainless steel), as well as carbon materials. Among these, copper or copper alloys are preferred.

[0075] 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.

[0076] The average thickness of the negative electrode substrate may be, for example, 2 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 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, or 10 μm.

[0077] The configuration of the negative electrode intermediate layer is not particularly limited; for example, it can be selected from the configurations exemplified for the positive electrode intermediate layer.

[0078] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer optionally contains optional components such as a conductive agent, binder, thickener, and filler. The optional components such as the conductive agent, binder, thickener, and filler can be selected from the materials exemplified above 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.

[0079] For the negative electrode active material, known negative electrode active materials can be used. For lithium-ion secondary batteries, materials capable of intercalating and releasing lithium ions are typically 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 metalloids such as silicon oxide, titanium oxide, and tin oxide; and Li4Ti5O 12 LiTiO 2、 Examples include titanium-containing oxides such as TiNb2O7; 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 are 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.

[0080] "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 between 0.33 nm and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite.

[0081] "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 wavelength 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 wavelength of 0.34 nm or more and less than 0.36 nm.

[0082] Here, the "discharge state" of the carbon material refers to a state in which sufficient lithium ions that can be absorbed and released during charging and discharging are released from the carbon material, which is the negative electrode active material. 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.

[0083] 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 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.

[0084] The content of the negative electrode active material in the negative electrode active material layer is preferably, for example, 60% to 99% by mass, and more preferably 90% to 98% by mass. 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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, 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 negative 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 impurities in the negative 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.

[0091] 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 one negative electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one 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 one 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 ​​one negative electrode active material layer may be, for example, 2 mg / cm². 2 More than 50mg / cm 2 The following is also acceptable: The lower limit of the mass per unit area of ​​one negative electrode active material layer is 3 mg / cm². 2 , 4 mg / cm³ 2 , 5 mg / cm³ 2 or 6 mg / cm³ 2 It may also be the case that the upper limit of the mass per unit area of ​​one negative electrode active material layer is 30 mg / cm³. 2 , 20 mg / cm³ 2 , 15 mg / cm³ 2 , 12 mg / cm³ 2 or 10 mg / cm³ 2 That's fine.

[0092] 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%.

[0093] (Method of 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 positive electrode manufacturing method 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 other processes. 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 or otherwise performing other processes.

[0094] (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.

[0095] 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.

[0096] Examples of inorganic compounds constituting 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.

[0097] Examples of binders used in the inorganic layer include those similar to those exemplified in the positive electrode active material layer.

[0098] 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 of the separator" refers to a volume-based value and means a measurement value obtained using a mercury porosimeter.

[0099] The average thickness of the separator may be, for example, 10 μm to 40 μm, or 15 μm to 30 μm.

[0100] 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.

[0101] (electrode body) As the electrode body, known structures such as wound electrode bodies and laminated electrode bodies can be used.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] (Non-aqueous electrolytes) A known non-aqueous electrolyte can be used. A non-aqueous electrolyte is a medium that carries charge transport ions (e.g., lithium ions) between the positive and negative electrodes and is substantially free of water. The water content in a 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.

[0106] (Non-aqueous electrolyte) A non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0107] 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.

[0108] A cyclic carbonate refers to a carbonate having a ring structure containing a carbonate group (-OC(=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 a cyclic carbonate, a saturated cyclic carbonate is preferred, and ethylene carbonate is more preferred.

[0109] 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.

[0110] The non-aqueous solvent preferably contains carbonate, and more preferably contains both cyclic carbonate and linear carbonate. The carbonate content in the non-aqueous solvent is preferably 80% to 100% by volume, may be 99% to 100% by volume, or 100% by volume. Using cyclic carbonate can promote the dissociation of the electrolyte salt and increase the ionic conductivity of the non-aqueous electrolyte. Using linear carbonate can keep the viscosity of the non-aqueous electrolyte low. When using both cyclic carbonate and linear carbonate, the volume ratio of cyclic carbonate to linear carbonate (cyclic carbonate:linear carbonate) is preferably in the range of 5:95 to 50:50.

[0111] Any known electrolyte salt can be used. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Among these, lithium salts are preferred. One or more electrolyte salts can be used.

[0112] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, and LiClO4; imide salts such as LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, and LiN(SO2CF3)(SO2C4F9); and lithium oxalate salts such as LiB(C2O4)2, LiBF2(C2O4), and LiPF2(C2O4)2. LiN(SO2F)2 is also an inorganic lithium salt. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred. Imide salts are also sometimes preferred.

[0113] The electrolyte salt content in the non-aqueous electrolyte is 0.1 mol / dm³ at 20°C and 1 atm. 3 More than 2.5mol / dm 3 The following is preferred: 0.3 mol / dm 3 More than 2.0mol / dm 3 The following is more preferable: 0.5 mol / dm 3More than 1.7mol / dm 3 The following is even more preferable: 0.7 mol / dm 3 More than 1.5mol / dm 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.

[0114] 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.

[0115] (solid electrolyte) The solid electrolyte can be selected from any material that has ionic conductivity, such as lithium, sodium, or calcium, and is solid at room temperature (e.g., 20°C). 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.

[0116] (container) The container houses the electrode body and non-aqueous electrolyte within its internal space. The container material can be a metal material such as aluminum or stainless steel, or a resin material; metal materials are preferred from the viewpoint of strength, etc. Composite materials of metal and resin materials can also be used.

[0117] 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.

[0118] (Shape, application, etc. of non-aqueous electrolyte energy storage elements) 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] <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 known methods. The manufacturing method of 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] <Energy storage device> The energy storage device 30 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 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. [Examples]

[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] (Fabrication of the positive electrode) A positive electrode mixture paste was prepared using lithium iron phosphate (LFP) as the positive electrode active material, acetylene black (AB) as the conductive agent, polyvinylidene fluoride (PVDF) as the binder, and N-methylpyrrolidone (NMP) as the dispersion medium. The mass ratio of LFP, AB, and PVDF was 94.5:3.0:2.5 on a solid content basis. Secondary particles of LFP with a carbon material coating on the surface were used. The average particle size of the LFP was 9.5 μm.

[0132] The positive electrode active material layer was formed by coating this positive electrode mixture paste onto aluminum foil, which served as the positive electrode substrate, drying it, and then roll-pressing it, thereby obtaining the positive electrode. The obtained positive electrode active material layer, by adjusting the average particle size of the LFP (lead phosphate foam) used as the positive electrode active material layer, as well as the drying conditions of the positive electrode mixture paste and the pressing pressure used to form the positive electrode active material layer, exhibited a log differential pore volume distribution curve as shown in Figure 3. This curve had a first peak in the range of pore diameters of 0.04 μm or less, and a second peak in the range of pore diameters between 0.1 μm and 1 μm. Table 1 shows the density of the positive electrode active material layer, the content of the conductive agent, the pore diameter at the first peak of the log differential pore volume distribution curve, the log differential pore volume at the first peak (first peak log differential pore volume), the pore diameter at the second peak, and the log differential pore volume at the second peak (second peak log differential pore volume).

[0133] (Fabrication 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 98.4:0.8:0.8 in terms of solid content. The negative electrode mixture paste was applied to copper foil, the negative electrode substrate, dried, and roll-pressed to form a negative electrode active material layer, thereby obtaining the negative electrode.

[0134] (Preparation of non-aqueous electrolytes) A non-aqueous solvent was prepared by mixing ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate in a volume ratio of 20:26.5:53.5, to which 0.8 mol / dm³ of LiFSI was added as the electrolyte salt. 3 LiPF6 at 0.1 mol / dm³ 3 A non-aqueous electrolyte was obtained by mixing at the specified concentrations.

[0135] (Separator) A polyethylene microporous membrane was used as the separator.

[0136] (Assembly of non-aqueous electrolyte energy storage elements) The positive electrode, negative electrode, and separator described above were stacked to create an electrode body. The obtained 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.

[0137] [Examples 2 to 4, Comparative Examples 1 to 9] Except for the contents of the positive electrode active material, conductive agent, and binder, the density of the positive electrode active material layer, the pore diameter at the first peak of the log differential pore volume distribution curve, the log differential pore volume at the first peak (first peak log differential pore volume), the pore diameter at the second peak, and the log differential pore volume at the second peak (second peak log differential pore volume) being as shown in Table 1, non-aqueous electrolyte energy storage elements of Examples 2 to 4 and Comparative Examples 1 to 9 were obtained in the same manner as in Example 1. In Comparative Example 3, the log differential pore volume distribution curve of the positive electrode active material layer did not have a second peak.

[0138] [evaluation] (Initial charge / discharge) The initial charge and discharge of each non-aqueous electrolyte energy storage element in the examples and comparative examples was performed 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 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.

[0139] (DC resistance at low temperatures) After the initial charge and discharge described above, each non-aqueous electrolyte energy storage element was subjected to constant current charging at a charging current of 1.0C in a temperature environment of 25°C, and its state of charge (SOC) was adjusted to 50%. Subsequently, each non-aqueous electrolyte energy storage element was stored in a constant temperature bath at -10°C for 4 hours, and then 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 at a current of 0.2C, and the SOC was adjusted to 50%. The relationship between the current in each charge and the voltage 10 seconds after the start of charging was plotted, and the DC resistance (DCR) was calculated from the slope of the straight line obtained from the three plots, and this was referred to as "Low-temperature DCR (-10°C)".

[0140] (60°C charge / discharge cycle test) After measuring the DC resistance at the low temperature described above, each non-aqueous electrolyte energy storage element underwent a charge-discharge cycle test in a constant temperature bath at 60°C according to the following procedure. Constant current and constant voltage charging was performed with a charging current of 1.0C and a charging termination voltage of 3.50V. The charging termination condition was defined as when the current decreased to 0.01C. A 10-minute rest period was then observed. Furthermore, constant current discharge was performed with a discharge current of 1.0C and a discharge termination voltage of 2.00V, followed by a 10-minute rest period. This charge-discharge cycle was performed 700 times. After the first constant current discharge cycle, the AC resistance (ACR) at 1kHz at 25°C was measured and defined as the "initial ACR". The AC resistance was measured using a known method.

[0141] (ACR increase rate after 60°C charge / discharge cycle test) After the 60°C charge-discharge cycle test described above, the AC resistance (ACR) at 1 kHz was measured for each non-aqueous electrolyte energy storage element at 25°C and defined as the "ACR after charge-discharge cycle." The AC resistance was measured using a known method. The "ACR increase rate" was calculated as the percentage of the ACR after the charge-discharge cycle relative to the initial ACR. Table 1 shows the low-temperature DCR (-10°C) and ACR increase rate for each non-aqueous electrolyte energy storage element in Examples 1 to 4 and Comparative Examples 1 to 9. In Comparative Examples 4 and 5, the charge-discharge capacity decreased rapidly during the 60°C charge-discharge cycle test, so the ACR increase rate could not be measured.

[0142] [Table 1]

[0143] As shown in Table 1, Comparative Examples 1 to 3, in which the pore diameter at the first peak was greater than 0.04 μm, had a low-temperature DCR of 250 mΩ or more. Comparative Examples 4 to 6, in which the conductive agent content was 2.0 mass% or less, had a low-temperature DCR of 250 mΩ or more and an ACR increase rate of 140% or more. In addition, the log differential pore volume at the second peak was 0.18 cm³. 3 Comparative Examples 7 to 9, which had values ​​greater than / g, showed an ACR increase rate of 140% or more. In contrast, the conductive agent content was greater than 2.0 mass%, the pore diameter at the first peak was 0.04 μm or less, and the log differential pore volume at the second peak was 0.18 cm³. 3 Examples 1 to 4, which were less than or equal to / g, had a low-temperature DCR of less than 250 mΩ and an ACR increase rate of less than 140%. [Industrial applicability]

[0144] 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. [Explanation of symbols]

[0145] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive lead 5. Positive external terminal 6 Negative lead 7. Negative external terminal 20 Energy storage units 30 Energy storage devices

Claims

1. The positive electrode comprises a polyanionic compound containing an iron element and a conductive agent in a positive electrode active material layer. The log differential pore volume distribution curve of the above positive electrode active material layer has a first peak in the range of pore diameter 0.04 μm or less, and a second peak in the range of pore diameter 0.1 μm or more and 1 μm or less. The log differential pore volume at the second peak mentioned above is 0.18 cm³. ３ / g or less, A positive electrode for a non-aqueous electrolyte energy storage element, wherein the conductive agent content in the positive electrode active material layer is greater than 2.0% by mass.

2. The system comprises a positive electrode substrate and a positive electrode active material layer laminated on the positive electrode substrate. The positive electrode for a non-aqueous electrolyte energy storage element according to claim 1, wherein the positive electrode substrate is made of aluminum.

3. The positive electrode for a non-aqueous electrolyte energy storage element according to claim 2, wherein the fracture strength of the polyanion compound is 40 MPa or more.

4. The log differential pore volume at the first peak mentioned above is 0.2 cm³. ３ A positive electrode for a non-aqueous electrolyte energy storage element according to any one of claims 1 to 3, wherein the amount is 1 / g or more.

5. A non-aqueous electrolyte energy storage element comprising a positive electrode for a non-aqueous electrolyte energy storage element according to any one of claims 1 to 3.

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