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

Abstract

To provide a positive electrode for a non-aqueous electrolyte power storage element, which is excellent in sufficient between a base material and a positive-electrode active material layer and the energy density of which is increased, and the non-aqueous electrolyte power storage element using the positive electrode for the non-aqueous electrolyte power storage element.SOLUTION: In a positive electrode 10 for a non-aqueous electrolyte power storage element according to one aspect of the present invention, a base material 11, a first active material layer 12 composed predominantly of a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure, and a second active material layer 13 composed predominantly of a polyanion compound having an olivine type crystal structure are provided in this order. The average thickness of the second active material layer 13 is greater than that of the first active material layer 12.SELECTED DRAWING: Figure 1

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 popularized.

[0003] As a positive electrode active material used in a non-aqueous electrolyte storage element, polyanion compounds having an olivine-type crystal structure such as lithium iron phosphate are known. Patent Document 1 describes a positive electrode for a non-aqueous electrolyte secondary battery in which a positive electrode active material layer containing LiFePO4 is provided on a current collector provided with a current collector coating layer containing carbon black on the surface of an aluminum foil.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The polyanion compound having an olivine-type crystal structure as a positive electrode active material has advantages such as excellent thermal stability. Here, in the production of a positive electrode for a non-aqueous electrolyte storage element, it is common to laminate a positive electrode active material layer on a substrate and perform pressing or the like to enhance the adhesion between the substrate and the positive electrode active material layer. By pressing, some of the particles of the positive electrode active material in the positive electrode active material layer can be embedded in the substrate, enhancing the adhesion, and as a result, the electron conductivity between the substrate and the positive electrode active material layer can also be improved. However, the polyanion compound having an olivine-type crystal structure is a relatively soft material compared to other positive electrode active materials. Therefore, even when pressing is performed as described above, the particles of the polyanion compound are not sufficiently embedded in the substrate, and it is difficult to enhance the adhesion. Thus, in order to enhance the adhesion between the positive electrode active material layer using the polyanion compound and the substrate, as described in Patent Document 1 above, a substrate (current collector) provided with a coating layer also referred to as a carbon coating layer or the like on the surface may be used. By using such a substrate, the particles of the polyanion compound are likely to be embedded in the relatively soft coating layer on the substrate surface, improving the adhesion. However, the substrate provided with the coating layer is expensive, and the use of such a substrate causes high costs. In addition, the polyanion compound having an olivine-type crystal structure tends to be inferior to other positive electrode active materials in terms of energy density, and the energy density of the positive electrode becomes lower due to the coating layer.

[0006] An object of the present invention is to provide a positive electrode for a non-aqueous electrolyte storage element using a polyanion compound having an olivine-type crystal structure, which has excellent thermal stability, sufficient adhesion between a substrate and a positive electrode active material layer, and an increased energy density, and a non-aqueous electrolyte storage element using such a positive electrode for a non-aqueous electrolyte storage element.

Means for Solving the Problems

[0007] The positive electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention includes a base material, a first active material layer mainly composed of a lithium transition metal composite oxide having an α-NaFeO₂-type crystal structure, and a second active material layer mainly composed of a polyanion compound having an olivine-type crystal structure, provided in this order, and the average thickness of the second active material layer is larger than the average thickness of the first active material layer.

[0008] The positive electrode for a non-aqueous electrolyte storage element according to another aspect of the present invention includes a base material, a first active material layer mainly composed of a lithium transition metal composite oxide having an α-NaFeO₂-type crystal structure, and a second active material layer mainly composed of a polyanion compound having an olivine-type crystal structure, provided in this order, and the content of the polyanion compound with respect to the total content of the lithium transition metal composite oxide and the polyanion compound is more than 50% by mass.

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

Advantages of the Invention

[0010] According to any one aspect of the present invention, there is provided a positive electrode for a non-aqueous electrolyte storage element in which a polyanion compound having an olivine-type crystal structure is used, which has excellent thermal stability, sufficient adhesion between the base material and the positive electrode active material layer, and a high energy density, and a non-aqueous electrolyte storage element using such a positive electrode for a non-aqueous electrolyte storage element.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0012] First, an overview of the positive electrode for a non-aqueous electrolyte storage element and the non-aqueous electrolyte storage element disclosed by this specification will be described.

[0013] [1] The positive electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention includes a base material, a first active material layer mainly composed of a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure, and a second active material layer mainly composed of a polyanion compound having an olivine type crystal structure, in this order, and the average thickness of the second active material layer is larger than the average thickness of the first active material layer.

[0014] The positive electrode for a non-aqueous electrolyte storage element described in [1] above is a positive electrode for a non-aqueous electrolyte storage element in which a polyanion compound having an olivine-type crystal structure is used. It has excellent thermal stability, sufficient adhesion between the base material and the positive electrode active material layer, and an increased energy density. In the positive electrode for a non-aqueous electrolyte storage element described in [1] above, both the first active material layer and the second active material layer are positive electrode active material layers. The reason for the above effects is not clear, but the following reasons are speculated. The particles of the lithium transition metal composite oxide having an α-NaFeO2-type crystal structure are harder than the particles of the polyanion compound having an olivine-type crystal structure. In the positive electrode for a non-aqueous electrolyte storage element described in [1] above, since the first active material layer mainly composed of such a lithium transition metal composite oxide is provided on the surface of the base material, the particles of the lithium transition metal composite oxide are likely to sink into the base material by pressing or the like, and as a result, sufficient adhesion to the base material is exhibited. Further, according to the positive electrode for a non-aqueous electrolyte storage element described in [1] above, compared with the positive electrode for a non-aqueous electrolyte storage element using a conventional polyanion compound having an olivine-type crystal structure, the energy density is increased because a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure is further used. And in the positive electrode for a non-aqueous electrolyte storage element described in [1] above, the average thickness of the second active material layer mainly composed of a polyanion compound having an olivine-type crystal structure is larger than the average thickness of the first active material layer mainly composed of a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure, and the content of the lithium transition metal composite oxide having an α-NaFeO2-type crystal structure as the positive electrode active material is relatively small, so that excellent thermal stability by the polyanion compound having an olivine-type crystal structure can be exhibited.

[0015] "Main component" refers to the component having the largest content on a mass basis. The "average thickness" of the first active material layer and the second active material layer refers to the average value of the thicknesses measured at any five locations in the cross-section of the measurement sample observed in the SEM image obtained using a scanning electron microscope (SEM). In the case where the first active material layer and the second active material layer are formed on both sides of the base material, the average value of the total thickness of the first active material layer and the second active material layer formed on both sides of the base material is defined as the average thickness. The main components of the first active material layer and the second active material layer are confirmed by observing the elemental distribution in the cross-section of the above-mentioned measurement sample using a scanning electron microscope - energy dispersive X-ray analyzer (SEM-EDX). The measurement sample is prepared according to the following procedure. First, the non-aqueous electrolyte storage element is charged at a constant current of 0.05C until the charging termination voltage during normal use is reached, and is brought to a fully charged state. After a 30-minute rest, it is discharged at a constant current of 0.05C until the discharge termination voltage during normal use is reached. It is disassembled and the positive electrode is taken out. The taken-out positive electrode is thoroughly washed with dimethyl carbonate and then dried under reduced pressure at room temperature. The dried positive electrode is fixed with a thermosetting resin. For the positive electrode fixed with the resin, a cross-section is exposed by the ion milling method to obtain a measurement sample. The operations from the disassembly of the non-aqueous electrolyte storage element to the preparation of the measurement sample are carried out in an argon atmosphere with a dew point of -60°C or lower. Here, "during normal use" refers to the case where the non-aqueous electrolyte storage element is used by adopting the charge-discharge conditions recommended or specified for the non-aqueous electrolyte storage element, and when a charger for the non-aqueous electrolyte storage element is prepared, it refers to the case where the non-aqueous electrolyte storage element is used by applying that charger. For the acquisition of the SEM image, JSM-7001F (manufactured by JEOL Ltd.) is used as the scanning electron microscope. The SEM image is to observe the secondary electron image. The acceleration voltage is set to 15 kV. In addition, various conditions such as the spot diameter, working distance, irradiation current, brightness, and focus are appropriately set so that the contour of the positive electrode becomes clear.

[0016] [2] The positive electrode for a non-aqueous electrolyte storage element according to another aspect of the present invention includes a base material, a first active material layer mainly composed of a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure, and a second active material layer mainly composed of a polyanion compound having an olivine type crystal structure, provided in this order, and the content of the polyanion compound with respect to the total content of the lithium transition metal composite oxide and the polyanion compound is more than 50% by mass.

[0017] The positive electrode for a non-aqueous electrolyte storage element according to the above [2] is a positive electrode for a non-aqueous electrolyte storage element in which a polyanion compound having an olivine type crystal structure is used, has excellent thermal stability, has sufficient adhesion between the base material and the positive electrode active material layer, and has an increased energy density. Also in the positive electrode for a non-aqueous electrolyte storage element according to the above [2], both the first active material layer and the second active material layer are positive electrode active material layers. The reason for the above effects is not clear, but it is presumed that the reason is the same as in the case of the positive electrode for a non-aqueous electrolyte storage element described in the above [1].

[0018] [3] In the positive electrode for a non-aqueous electrolyte storage element according to the above [1] or [2], the polyanion compound may be lithium iron manganese phosphate.

[0019] The positive electrode for a non-aqueous electrolyte storage element according to the above [3] can further increase the energy density by using lithium iron manganese phosphate as the polyanion compound.

[0020] [4] In the positive electrode for a non-aqueous electrolyte storage element according to any one of the above [1] to [3], the lithium transition metal composite oxide may be a lithium nickel cobalt manganese composite oxide.

[0021] The positive electrode for a non-aqueous electrolyte storage element according to the above [4] can further increase the adhesion between the base material and the positive electrode active material layer and further increase the energy density by using a lithium nickel cobalt manganese composite oxide as the lithium transition metal composite oxide.

[0022] [5] In the positive electrode for a non-aqueous electrolyte storage element according to any one of [1] to [4] above, the average thickness of the first active material layer may be 10% or less of the average thickness of the second active material layer.

[0023] In the positive electrode for a non-aqueous electrolyte storage element according to [5] above, since the first active material layer mainly composed of a lithium transition metal composite oxide is relatively very thin and the second active material layer mainly composed of a polyanion compound has a relatively sufficient thickness, good performance due to the polyanion compound such as thermal stability can be particularly sufficiently exhibited.

[0024] [6] In the positive electrode for a non-aqueous electrolyte storage element according to any one of [1] to [5] above, the average particle diameter of the lithium transition metal composite oxide may be 5 μm or more.

[0025] According to the positive electrode for a non-aqueous electrolyte storage element described in [6] above, since the particle diameter of the lithium transition metal composite oxide, which is the main component of the first active material layer, is relatively large and can be particularly sufficiently embedded in the base material by pressing or the like, the adhesion between the base material and the positive electrode active material layer can be enhanced.

[0026] The average particle diameter means a value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) becomes 50% based on the particle size distribution measured by the laser diffraction / scattering method with respect to a dilution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0027] The measurement of the average particle size of the lithium transition metal composite oxide is carried out on the lithium transition metal composite oxide before charge and discharge, or on the lithium transition metal composite oxide contained in the positive electrode for the non-aqueous electrolyte energy storage element of the non-aqueous electrolyte energy storage element, for the one processed by the following procedure. First, the non-aqueous electrolyte energy storage element is charged at a constant current with a charging current of 0.05C until the charging cut-off voltage during normal use is reached to make it in a fully charged state. After a 30-minute rest, it is discharged at a constant current with a discharge current of 0.05C until the discharge cut-off voltage during normal use. It is disassembled, the positive electrode is taken out, and a test cell is assembled with the taken-out positive electrode as the working electrode and a metallic lithium electrode as the counter electrode. For the metallic lithium electrode here, pure metallic lithium is used. For the test cell, constant current discharge is carried out at a current of 10 mA per 1 g of the positive electrode active material until the positive electrode potential reaches 3.0 V (vs. Li / Li + ) to adjust the positive electrode to a fully discharged state. It is disassembled again, and the positive electrode is taken out. The taken-out positive electrode is washed with dimethyl carbonate. Then, the positive electrode active material layer (the first active material layer and the second active material layer) containing the lithium transition metal composite oxide is peeled off from the substrate, and the positive electrode active material layer is washed with a solvent capable of dissolving the binder to remove the binder. The washed positive electrode active material layer is immersed in an acid or alkali solution to remove the metal derived from the substrate and the SEI (solid electrolyte interface) film, etc. Then, it is washed with water and dried under reduced pressure at room temperature for 24 hours to collect the positive electrode active material. In collecting the lithium transition metal composite oxide, when peeling the positive electrode active material layer from the substrate, only the first active material layer may be taken out and only the lithium transition metal composite oxide may be collected as the positive electrode active material. Also, the first active material layer and the second active material layer may be peeled off integrally and the polyanion compound may be collected together with the lithium transition metal composite oxide as the positive electrode active material. The obtained positive electrode active material (only the lithium transition metal composite oxide or the lithium transition metal composite oxide and the polyanion compound) is used for measurement. The operations from the disassembly of the non-aqueous electrolyte energy storage element to the collection of the positive electrode active material are carried out in an argon atmosphere with a dew point of -60°C or lower.

[0028] [7] In the positive electrode for a non-aqueous electrolyte storage element according to any one of [1] to [6] above, the base material may have a metal layer, and the first active material layer and the metal layer may be directly laminated.

[0029] Since the positive electrode for a non-aqueous electrolyte storage element according to [7] above has a structure in which the positive electrode active material layer is laminated without providing a carbon coating layer or the like on the metal layer of the base material, the manufacturing cost can be suppressed, and the energy density of the positive electrode can be further increased. Further, in the positive electrode for a non-aqueous electrolyte storage element according to [7] above, although the positive electrode active material layer is directly laminated on the metal layer of the base material, sufficient adhesion is provided between the base material and the positive electrode active material layer.

[0030] [8] A non-aqueous electrolyte storage element according to another aspect of the present invention includes the positive electrode for a non-aqueous electrolyte storage element according to any one of [1] to [7] above.

[0031] The non-aqueous electrolyte storage element according to [8] above is a positive electrode for a non-aqueous electrolyte storage element in which a polyanion compound having an olivine-type crystal structure is used, has excellent thermal stability, has sufficient adhesion between the base material and the positive electrode active material layer, and has an increased energy density. Therefore, it has excellent thermal stability and good charge-discharge performance and the like.

[0032] The positive electrode for a non-aqueous electrolyte storage element, non-aqueous electrolyte storage element, power storage device, method for manufacturing a non-aqueous electrolyte storage element, and other embodiments according to an embodiment of the present invention will be described in detail. Note that the names of the respective constituent members (each constituent element) used in each embodiment may be different from the names of the respective constituent members (each constituent element) used in the background art.

[0033] <Positive Electrode for Non-Aqueous Electrolyte Storage Element> The positive electrode for a non-aqueous electrolyte storage element according to an embodiment of the present invention (hereinafter, also simply referred to as "positive electrode") includes a base material, a first active material layer, and a second active material layer in this order. In one embodiment of the present invention, like the positive electrode 10 for a non-aqueous electrolyte storage element shown in FIG. 1, the first active material layer 12 and the second active material layer 13 may be provided in this order on both surfaces of the base material 11. In another embodiment of the present invention, the first active material layer and the second active material layer may be provided in this order only on one surface side of the base material. In the positive electrode, other layers may be further provided between the base material and the first active material layer, between the first active material layer and the second active material layer, and the like. In the positive electrode, a layer covering the second active material layer may be provided. The positive electrode may be composed only of the base material, the first active material layer, and the second active material layer.

[0034] The positive electrode according to an embodiment of the present invention is a positive electrode for a non-aqueous electrolyte storage element, may be a positive electrode for a non-aqueous electrolyte storage element, or may be a positive electrode for a lithium-ion secondary battery.

[0035] The base material (hereinafter, the base material of the positive electrode is also referred to as "positive electrode base material") has conductivity. Whether it has "conductivity" is determined with a volume resistivity measured in accordance with JIS-H-0505 (1975) having 10 -2 Ω·cm as a threshold value. As the material of the positive electrode base material, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferable from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode base material include a foil, a vapor deposition film, a mesh, and a porous material, and a foil is preferable from the viewpoint of cost. As the positive electrode base material, an aluminum foil or an aluminum alloy foil is preferable. Examples of aluminum or an aluminum alloy include A1085, A3003, A1N30, etc. defined in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0036] The positive electrode substrate may have a metal layer or may consist only of a metal layer. When a positive electrode substrate consisting only of a metal layer is used, the positive electrode substrate can be made thinner, and the positive electrode can be miniaturized and the energy density per unit volume can be increased. Examples of the material of the metal layer include those described above as the material of the positive electrode substrate, and aluminum or an aluminum alloy is preferable. The average thickness of the metal layer is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, still more preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. The positive electrode substrate may be composed of a metal layer and a coating layer that coats the metal layer. The coating layer may be, for example, a carbon coating layer containing a carbon material and a binder. The positive electrode substrate may have a single-layer structure or a multilayer structure.

[0037] The average thickness of the positive electrode substrate is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, still more preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while increasing the energy density of the non-aqueous electrolyte storage element.

[0038] The first active material layer is laminated directly on the substrate or via another layer. In one embodiment of the present invention, the substrate has a metal layer, and the first active material layer and the metal layer of the substrate may be laminated directly. Further, the substrate may consist only of a metal layer (the substrate is a metal substrate), and the first active material layer and the substrate may be laminated directly.

[0039] The first active material layer is mainly composed of a lithium transition metal composite oxide having an α-NaFeO2 type crystal structure (hereinafter, also simply referred to as "lithium transition metal composite oxide"). The first active material layer may contain optional components such as a conductive agent, a binder, a thickener, and a filler, as necessary.

[0040] The lithium transition metal composite oxide is a cathode active material. The lithium transition metal composite oxide preferably contains at least one of nickel element, cobalt element and manganese element, and more preferably contains nickel element, cobalt element and manganese element. The lithium transition metal composite oxide is preferably a lithium nickel cobalt manganese composite oxide. By using such a compound as the lithium transition metal composite oxide, the adhesion between the base material and the cathode active material layer can be further enhanced, and the energy density can be further increased. The lithium transition metal composite oxide may contain other transition metal elements other than nickel element, cobalt element and manganese element, and may further contain elements other than transition metal elements, lithium element and oxygen element (such as aluminum element).

[0041] As the lithium transition metal composite oxide, a compound represented by the following formula (1) is preferred. Li 1+α M 1 1-α O2···(1) In formula (1), M 1 is a metal element containing a transition metal element (excluding Li). -0.05 ≦ α < 1.

[0042] M in formula (1) 1 preferably contains at least one of Ni, Co and Mn, more preferably contains Ni, Co and Mn, even more preferably is substantially composed of the three elements of Ni, Co and Mn, and still more preferably is composed of the three elements of Ni, Co and Mn. M 1 may contain other metal elements. The other metal elements may be transition metal elements or typical metal elements.

[0043] In formula (1), the content of the molar ratio of Ni to M (Ni / M 1 1 ) is preferably 0.1 or more and 0.9 or less, more preferably 0.2 or more and 0.7 or less, and may be 0.3 or more and 0.5 or less.)

[0044] In formula (1), M 1 The content of the molar ratio of Co to M (Co / M 1 ) is preferably 0.1 or more and 0.9 or less, more preferably 0.2 or more and 0.7 or less, and may be 0.3 or more and 0.5 or less.

[0045] In formula (1), M 1 The content of the molar ratio of Mn to M (Mn / M 1 ) is preferably 0.1 or more and 0.9 or less, more preferably 0.2 or more and 0.7 or less, and may be 0.3 or more and 0.5 or less.

[0046] In formula (1), M 1 The content of the total molar ratio of Ni, Co, and Mn to M ((Ni + Co + Mn) / M 1 )) is preferably 0.9 or more and 1.0 or less, and more preferably 0.99 or more and 1.00 or less.

[0047] In formula (1), M 1 The molar ratio of Li to M (Li / M 1 ), that is, the upper limit of (1 + α) / (1 - α) is preferably 1.6, and may be more preferably 1.5, 1.4, 1.2, 1.1, or 1.05. The lower limit of the molar ratio (Li / M 1 ) is preferably 0.95, and more preferably 1.0. The molar ratio (Li / M 1 ) may be in the range combined with any of the above-mentioned lower limits and any of the above-mentioned upper limits. The molar ratio (Li / M 1 ) may be 1. That is, α may be 0.

[0048] Examples of the lithium transition metal composite oxide include, for example, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 1 / 3Co 1 / 3 Mn 1 / 3 O2, LiNi 0.8 Co 0.15 Al 0.05 Examples thereof include O2, LiNiCoAlO2, LiNiO2, LiCoO2, etc. One or more lithium transition metal composite oxides can be used.

[0049] In addition, the analysis of the constituent element composition of the positive electrode active material (lithium transition metal composite oxide and polyanion compound described later) is performed on the positive electrode active material before charge and discharge, or for the positive electrode active material contained in the positive electrode for non-aqueous electrolyte storage element of the non-aqueous electrolyte storage element, it is performed on the material processed by the same procedure as when measuring the average particle size of the above-described lithium transition metal composite oxide.

[0050] The lithium transition metal composite oxide is usually in the form of particles (powder). The lithium transition metal composite oxide may be secondary particles formed by aggregation of a plurality of primary particles, may be single particles in which the primary particles exist independently, or may be a mixed form thereof. As the lower limit of the average particle size of the lithium transition metal composite oxide, for example, it may be 1 μm or 3 μm, but 5 μm is preferable, and 7 μm is more preferable. By setting the average particle size of the lithium transition metal composite oxide to be equal to or greater than the above lower limit, the lithium transition metal composite oxide can easily penetrate into the substrate and the adhesion to the substrate can be enhanced. As the upper limit of the average particle size of the lithium transition metal composite oxide, 20 μm is preferable, and 15 μm is more preferable. The average particle size of the lithium transition metal composite oxide may be in the range obtained by combining any of the above lower limits and any of the above upper limits.

[0051] In order to obtain powder with a predetermined particle size, a pulverizer, a classifier, etc. are used. Examples of the pulverization method include methods using a mortar, a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, etc. Wet pulverization in which water or an organic solvent such as hexane coexists can also be used during pulverization. As the classification method, a sieve, an air classifier, etc. are used as needed for both dry and wet processes.

[0052] The content of the lithium transition metal composite oxide in the first active material layer is preferably 70% by mass or more and 99% by mass or less, more preferably 80% by mass or more and 98% by mass or less, and still more preferably 85% by mass or more and 95% by mass or less. By setting the content of the lithium transition metal composite oxide within the above range, the adhesion to the substrate, the energy density, etc. can be enhanced.

[0053] The first active material layer may further contain other positive electrode active materials other than the lithium transition metal composite oxide. Examples of the other positive electrode active materials include conventionally known positive electrode active materials used in non-aqueous electrolyte storage elements, and may also be polyanion compounds described later. However, the lower limit of the content of the lithium transition metal composite oxide with respect to all the positive electrode active materials in the first active material layer is preferably 80% by mass, more preferably 90% by mass, and still more preferably 95% by mass. The upper limit of the content of the lithium transition metal composite oxide with respect to all the positive electrode active materials in the first active material layer may be 100% by mass. The content of the lithium transition metal composite oxide with respect to all the positive electrode active materials in the first active material layer may be in the range combined with any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0054] The conductive agent is not particularly limited as long as it is a material having conductivity. Examples of such conductive agents include carbon materials, metals, conductive ceramics, and the like. Examples of carbon materials include graphite, non-graphitic carbon, graphene-based carbon, and the like. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, carbon black, and the like. Examples of carbon black include furnace black, acetylene black, ketjen black, and the like. Examples of graphene-based carbon include graphene, carbon nanotubes, fullerenes, and the like. Examples of the shape of the conductive agent include powder form, fibrous form, and the like. As the conductive agent, one of these materials may be used alone, or two or more of them may be mixed and used. Further, these materials may be used in a composite form. For example, a material obtained by compositing carbon black and carbon nanotubes may be used. Among these, carbon black is preferable from the viewpoints of electron conductivity and coatability, and acetylene black is particularly preferable.

[0055] The content of the conductive agent in the first 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. By setting the content of the conductive agent within the above range, the energy density of the non-aqueous electrolyte storage element can be increased.

[0056] Examples of the binder include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, polyimide, etc.; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, etc.; polysaccharide polymers, and the like.

[0057] The content of the binder in the first active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 9% by mass or less. By setting the content of the binder within the above range, the lithium transition metal composite oxide can be stably held.

[0058] Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like. In one embodiment of the present invention, the first active material layer may not contain a thickener.

[0059] The filler is not particularly limited. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, and magnesium oxide, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, and mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. In one embodiment of the present invention, the first active material layer may not contain a filler.

[0060] The first active material layer may contain typical non-metal elements such as B, N, P, F, Cl, Br, and I, typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, and Nb as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0061] The average thickness of the first active material layer is preferably, for example, 1 μm or more and 20 μm or less, more preferably 2 μm or more and 15 μm or less, and may be 5 μm or more and 12 μm or less.

[0062] The second active material layer is laminated directly or via another layer on the surface of the first active material layer opposite to the base material. In one embodiment of the present invention, the second active material layer and the first active material layer may be directly laminated.

[0063] The second active material layer contains, as a main component, a polyanion compound having an olivine-type crystal structure (hereinafter, also simply referred to as "polyanion compound"). The second active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, if necessary. The optional components such as the conductive agent, the binder, the thickener, and the filler in the second active material layer can be selected from the materials exemplified in the first active material layer. The content of each of these optional components in the second active material layer is the same as the content of these optional components in the first active material layer described above.

[0064] The polyanion compound is a positive electrode active material. The polyanion compound is composed of a polyanion (that is, a polyvalent anion) and a cation. The polyanion compound may be a compound containing a lithium element and a transition metal element. Examples of the polyanion compound include compounds containing an oxoacid anion (PO4 3- , SO4 2- , SiO4 4- , BO3 3- , VO4 3- etc.) that is a polyanion, lithium ions, and transition metal ions. The polyanion compound may further contain other elements (for example, a halogen element, etc.). As the transition metal element contained in the polyanion compound, an iron element, a manganese element, a nickel element, and a cobalt element are preferable, and a manganese element and an iron element are more preferable. As the oxoacid anion contained in the polyanion compound, a phosphate anion (PO4 3- ) is preferable.

[0065] The polyanion compound is preferably a compound represented by the following formula (2). Li a M 2 b (AO c ) d X e ···(2) In formula (2), M 2M is at least one transition metal element. A is at least one selected from B, Al, Si, P, S, Cl, Ti, V, Cr, Mo, and W. X is at least one halogen element. a, b, c, d, and e are numbers satisfying 0 < a ≤ 3, 0 < b ≤ 2, 2 ≤ c ≤ 4, 1 ≤ d ≤ 3, and 0 ≤ e ≤ 1. a, b, c, d, and e may all be integers or may be decimals.

[0066] M in formula (2) 2 is preferably any one of Fe, Mn, Ni, and Co, or a combination of any two of these. M 2 preferably contains Mn and Fe, and more preferably consists of Mn and Fe. As A, P is preferred. In one embodiment, a = 1, b = 1, c = 4, d = 1, and e = 0 may be preferred in some cases.

[0067] Specific examples of the polyanion compound include, for example, LiFePO4, LiCoPO4, LiFe x Co 1-x PO4 (0 < x < 1), LiMnPO4, LiNiPO4, LiMn x Fe 1-x PO4 (0 < x < 1), LiCrPO4, LiFeVO4, Li2FeSiO4, Li2Fe2(SO4)3, LiFeBO3, LiFePO 3.9 F 0.2 , Li2MnSiO4, Li2CoPO4F, etc. The atoms or polyanions in these polyanion compounds may be partially substituted with other atoms or anion species. As the polyanion compound, lithium manganese iron phosphate (LiMn x Fe 1-x PO4) is preferred. Lithium manganese iron phosphate may be one in which some of the atoms or polyanions constituting lithium manganese iron phosphate are substituted with other atoms or anion species. One or more polyanion compounds can be used.

[0068] The polyanion compound is usually in the form of particles (powder). The surface of the polyanion compound particles may be coated with other materials (such as carbon materials, etc.). The polyanion compound may be secondary particles formed by aggregation of a plurality of primary particles, may be single particles in which the primary particles exist independently, or may be a mixed form thereof. The average particle size of the polyanion compound may be, for example, 0.1 μm or more and 20 μm or less, or may be 1 μm or more and 10 μm or less. By setting the average particle size of the polyanion compound to be not less than the above lower limit, the production or handling of the polyanion compound becomes easier. By setting the average particle size of the polyanion compound to be not more than the above upper limit, the electron conductivity of the second active material layer is improved.

[0069] The content of the polyanion compound in the second active material layer is preferably 70% by mass or more and 99% by mass or less, more preferably 80% by mass or more and 98% by mass or less, and even more preferably 85% by mass or more and 95% by mass or less. By setting the content of the polyanion compound within the above range, the thermal stability, energy density, etc. can be enhanced.

[0070] The second active material layer may further contain other positive electrode active materials other than the polyanion compound. Examples of other positive electrode active materials include conventionally known positive electrode active materials used in non-aqueous electrolyte storage elements, and may be the above-described lithium transition metal composite oxides. However, the lower limit of the content of the polyanion compound with respect to all the positive electrode active materials in the second active material layer is preferably 80% by mass, more preferably 90% by mass, and even more preferably 95% by mass. The upper limit of the content of the polyanion compound with respect to all the positive electrode active materials in the second active material layer may be 100% by mass. The content of the polyanion compound with respect to all the positive electrode active materials in the second active material layer may be in the range combined with any of the above-described lower limits and any of the above-described upper limits.

[0071] The second active material layer may contain, as components other than the positive electrode active material, conductive agent, binder, thickener, and filler, typical non-metal elements such as B, N, P, F, Cl, Br, I, etc., typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, etc., and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W, etc.

[0072] As the average thickness of the second active material layer, for example, 5 μm or more and 300 μm or less is preferable, 10 μm or more and 200 μm or less is more preferable, and 20 μm or more and 150 μm or less may be sufficient.

[0073] In one embodiment of the present invention, the average thickness of the second active material layer is greater than the average thickness of the first active material layer. The upper limit of the average thickness of the first active material layer with respect to the average thickness of the second active material layer (100%) is preferably 50%, more preferably 20%, still more preferably 10%, and may be 5%. By setting the average thickness of the first active material layer with respect to the average thickness of the second active material layer to be equal to or less than the above upper limit, the advantages (such as thermal stability) of the polyanion compound, which is the main component of the second active material layer, can be fully exhibited. The lower limit of the average thickness of the first active material layer with respect to the average thickness of the second active material layer (100%) is preferably 1%, more preferably 3%, and may be 5%. By setting the average thickness of the first active material layer with respect to the average thickness of the second active material layer to be equal to or greater than the above lower limit, the adhesion to the base material and the energy density by the first active material layer mainly composed of the lithium transition metal composite oxide can be further increased, etc. The average thickness of the first active material layer with respect to the average thickness of the second active material layer may be in the range of any combination of the above-mentioned lower limit and the above-mentioned upper limit.

[0074] In another embodiment of the present invention, the content of the polyanion compound relative to the total content of the lithium transition metal composite oxide and the polyanion compound is more than 50% by mass. The lower limit of the content of the polyanion compound relative to the total content of the lithium transition metal composite oxide and the polyanion compound is preferably 70% by mass, more preferably 80% by mass, and even more preferably 90% by mass. By setting the content of the polyanion compound relative to the total content of the lithium transition metal composite oxide and the polyanion compound to be not less than the above lower limit, the advantages (such as thermal stability) of the polyanion compound can be fully exhibited. The upper limit of the content of the polyanion compound relative to the total content of the lithium transition metal composite oxide and the polyanion compound is preferably 99% by mass, more preferably 97% by mass, and may be 95% by mass. By setting the content of the polyanion compound relative to the total content of the lithium transition metal composite oxide and the polyanion compound to be not more than the above upper limit, the adhesion to the substrate and the energy density by the lithium transition metal composite oxide can be further increased, etc. The content of the polyanion compound relative to the total content of the lithium transition metal composite oxide and the polyanion compound may be in the range obtained by combining any of the above lower limits and any of the above upper limits.

[0075] The positive electrode can be fabricated, for example, by sequentially coating a positive electrode binder paste for forming a first active material layer and a positive electrode binder paste for forming a second active material layer on a positive electrode substrate, thereby sequentially laminating the first active material layer and the second active material layer on the positive electrode substrate. The positive electrode binder paste for forming the first active material layer usually contains each component constituting the first active material layer and a dispersion medium. Similarly, the positive electrode binder paste for forming the second active material layer usually contains each component constituting the second active material layer and a dispersion medium. After coating the positive electrode binder paste, it is preferable to perform drying and pressing. By pressing, a positive electrode with high adhesion between the positive electrode substrate and the positive electrode active material layers (the first active material layer and the second active material layer) can be obtained. Drying and pressing after coating may be performed respectively after each coating of the positive electrode binder paste for forming the first active material layer and the positive electrode binder paste for forming the second active material layer. Also, only drying may be performed after coating the positive electrode binder paste for forming the first active material layer, and drying and pressing may be performed after each coating of the positive electrode binder paste for forming the second active material layer. After coating the positive electrode binder paste for forming the first active material layer, the positive electrode binder paste for forming the second active material layer may be coated without drying, and drying and pressing may be performed together.

[0076] <Non-aqueous electrolyte energy storage element> A non-aqueous electrolyte energy storage element (hereinafter, also simply referred to as an "energy storage element") according to an embodiment of the present invention includes an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container for housing the electrode body and the non-aqueous electrolyte. The electrode body is usually of a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked via a separator, or a wound type in which a positive electrode and a negative electrode are wound in a state of being stacked via a separator. At least a part of the non-aqueous electrolyte exists in a state of being impregnated into the voids of the positive electrode, the negative electrode, and the separator. As an example of the non-aqueous electrolyte energy storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as a "secondary battery") will be described.

[0077] (Positive electrode) The positive electrode provided in the non-aqueous electrolyte energy storage element according to an embodiment of the present invention can use the one described above as the positive electrode according to an embodiment of the present invention.

[0078] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed directly or via an intermediate layer on the negative electrode substrate. The configuration of the intermediate layer is not particularly limited, and for example, it contains a binder and a conductive agent.

[0079] The negative electrode substrate has conductivity. As the material of the negative electrode substrate, metals such as copper, nickel, stainless steel, nickel-plated steel, aluminum, or alloys thereof, carbon materials, etc. are used. Among these, copper or a copper alloy is preferable. Examples of the negative electrode substrate include a foil, a vapor deposition film, a mesh, a porous material, etc., and a foil is preferable from the viewpoint of cost. Therefore, a copper foil or a copper alloy foil is preferable as the negative electrode substrate. Examples of the copper foil include a rolled copper foil, an electrolytic copper foil, etc.

[0080] The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, still more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density of the non-aqueous electrolyte storage element.

[0081] [[ID=ID=13]]The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer may contain optional components such as a conductive agent, a binder, a thickener, a filler, etc. as necessary. The optional components such as a conductive agent, a binder, a thickener, a filler, etc. can be selected from the materials exemplified for the above positive electrode.

[0082] The negative electrode active material layer may contain typical non-metal elements such as B, N, P, F, Cl, Br, I, etc., typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, etc., and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W, etc. as components other than the negative electrode active material, the conductive agent, the binder, the thickener, and the filler.

[0083] The negative electrode active material can be appropriately selected from known negative electrode active materials. As the negative electrode active material for a lithium-ion secondary battery, a material capable of occluding and releasing lithium ions is usually used. Examples of the negative electrode active material include metallic lithium; metals or semi-metals such as Si and Sn; metal oxides or semi-metal oxides such as silicon oxide, titanium oxide, and tin oxide; Li4Ti5O 12 , LiTiO 2、 Titanium-containing oxides such as TiNb2O7; polyphosphoric acid compounds; silicon carbide; carbon materials such as graphite (graphite), non-graphitic carbon (easily graphitizable carbon or hardly graphitizable carbon), etc. Among these materials, carbon materials are preferred, graphite or non-graphitic carbon is more preferred, and graphite is even more preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more of them may be mixed and used.

[0084] "Graphite" refers to a carbon material having an average lattice plane spacing (d 002 ) of the (002) plane determined by X-ray diffraction method of 0.33 nm or more and less than 0.34 nm before charge and discharge or in the discharged state. Examples of graphite include natural graphite and artificial graphite. From the viewpoint of obtaining a material with stable physical properties, artificial graphite is preferred.

[0085] "Non-graphitic carbon" refers to a carbon material having an average lattice plane spacing (d 002 ) of the (002) plane determined by X-ray diffraction method of 0.34 nm or more and 0.42 nm or less before charge and discharge or in the discharged state. Examples of non-graphitic carbon include hardly graphitizable carbon and easily graphitizable carbon. Examples of non-graphitic carbon include materials derived from resins, petroleum pitch or materials derived from petroleum pitch, petroleum coke or materials derived from petroleum coke, plant-derived materials, alcohol-derived materials, etc.

[0086] Here, the "discharged state" of the carbon material means a state in which lithium ions that can be occluded and released during charge and discharge are sufficiently released from the carbon material that is the negative electrode active material. For example, in a half-cell using a negative electrode containing a carbon material as the working electrode and metallic lithium as the counter electrode, it is a state where the open circuit voltage is 0.7 V or higher.

[0087] "Graphitization-resistant carbon" refers to a carbon material where the above d 002 is 0.36 nm or more and 0.42 nm or less.

[0088] "Graphitization-easy carbon" refers to a carbon material where the above d 002 is 0.34 nm or more and less than 0.36 nm.

[0089] The negative electrode active material is usually particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, or a polyphosphoric acid compound, its average particle size may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, a Si oxide, or a Sn oxide, etc., its average particle size may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or greater than the above lower limit, the production or handling of the negative electrode active material becomes easy. By setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit, the electron conductivity of the negative electrode active material layer is improved. To obtain powder with a predetermined particle size, a pulverizer, a classifier, etc. are used. The pulverization method and the classification method can be selected, for example, from the methods exemplified for the above positive electrode. 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 a foil.

[0090] The content of the negative electrode active material in the negative electrode active material layer is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0091] 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, 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 may be 2% by mass or less. In one embodiment of the present invention, the negative electrode active material layer may not contain a conductive agent.

[0092] When the negative electrode active material layer contains a binder, the content of the binder in the negative electrode active material layer is preferably 1% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 8% by mass or less.

[0093] When the negative electrode active material layer contains a thickener, the content of the thickener in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 8% by mass or less. The content of the thickener in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less.

[0094] When the negative electrode active material layer contains a filler, the content of the filler 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, more preferably 2% by mass or less. In one embodiment of the present invention, the negative electrode active material layer may not contain a filler.

[0095] (Separator) The separator can be appropriately selected from known separators. As the separator, for example, a separator composed only of a base material layer, a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one or both surfaces of the base material layer, etc. can be used. Examples of the shape of the base material layer of the separator include woven fabric, non-woven fabric, porous resin film, etc. Among these shapes, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of the liquid retention property of the non-aqueous electrolyte. As the material of the base material layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of the shutdown function, and polyimides, aramids, etc. are preferable from the viewpoint of oxidation decomposition resistance. As the base material layer of the separator, a material in which these resins are compounded may be used.

[0096] The heat-resistant particles contained in the heat-resistant layer preferably have a mass reduction of 5% or less when heated from room temperature to 500 °C in an air atmosphere at 1 atm, and more preferably have a mass reduction of 5% or less when heated from room temperature to 800 °C. Examples of materials with a mass reduction of a predetermined value or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica, or artificial products thereof, etc. As the inorganic compound, these substances may be used alone or in combination, or two or more of them may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of the safety of the non-aqueous electrolyte storage element.

[0097] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and preferably 20% by volume or more from the viewpoint of discharge performance. Here, the "porosity" is a value based on volume and means the measured value by a mercury porosimeter.

[0098] As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of the polymer include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinyl pyrrolidone, polyvinylidene fluoride, and the like. Using a polymer gel has the effect of suppressing liquid leakage. As the separator, a porous resin film or non-woven fabric as described above may be used in combination with a polymer gel.

[0099] (Non-aqueous electrolyte) The non-aqueous electrolyte can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0100] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, nitriles, and the like. As the non-aqueous solvent, those in which some of the hydrogen atoms contained in these compounds are substituted with halogens may be used.

[0101] Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, and the like. Among these, EC is preferred.

[0102] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, and the like. Among these, EMC is preferred.

[0103] As the non-aqueous solvent, it is preferable to use a cyclic carbonate or a chain carbonate, and it is more preferable to use a cyclic carbonate and a chain carbonate in combination. By using a cyclic carbonate, dissociation of the electrolyte salt can be promoted to improve the ionic conductivity of the non-aqueous electrolyte. By using a chain carbonate, the viscosity of the non-aqueous electrolyte can be kept low. When using a cyclic carbonate and a chain carbonate in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0104] The electrolyte salt can be appropriately selected from known electrolyte salts. Usually, a lithium salt is used as the electrolyte salt.

[0105] Examples of the lithium salt include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, LiN(SO2F)2, lithium oxalate salts such as lithium bis(oxalato)borate (LiBOB), lithium difluorooxalate borate (LiFOB), lithium bis(oxalato)difluorophosphate (LiFOP), and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0106] The content of the electrolyte salt in the non-aqueous electrolyte is 0.1 mol / dm 3 or more and 2.5 mol / dm 3It is preferably the following, 0.3 mol / dm 3 or more and 2.0 mol / dm 3 or less, more preferably the following, 0.5 mol / dm 3 or more and 1.7 mol / dm 3 or less, even more preferably the following, 0.7 mol / dm 3 or more and 1.5 mol / dm 3 or less, which is particularly preferable. By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0107] In addition to non-aqueous solvents and electrolyte salts, the non-aqueous electrolyte may contain additives. Examples of the additives include halogenated carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC); oxalates such as lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis(oxalate) difluorophosphate (LiFOP); imide salts such as lithium bis(fluorosulfonyl) imide (LiFSI); aromatic compounds such as biphenyl, alkyl biphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partially halogenated compounds of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propenesultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butenesultone, perfluorooctane, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, tetrakis(trimethylsilyl) titanate, lithium monofluorophosphate, and lithium difluorophosphate. These additives may be used alone or in combination of two or more kinds.

[0108] The content of the additive contained 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, still 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 with respect to the mass of the entire non-aqueous electrolyte. By setting the content of the additive within the above range, the capacity retention performance or cycle performance after high-temperature storage can be improved, or the safety can be further improved.

[0109] A solid electrolyte may be used for the non-aqueous electrolyte, or a non-aqueous electrolyte and a solid electrolyte may be used in combination.

[0110] As the solid electrolyte, any material having ion conductivity such as lithium, sodium, and calcium and being solid at normal temperature (for example, from 15°C to 25°C) can be selected. Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and polymer solid electrolytes.

[0111] Examples of the sulfide solid electrolyte include Li2S-P2S5, LiI-Li2S-P2S5, and Li 10 Ge-P2S 12 and the like.

[0112] The shape of the non-aqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include cylindrical batteries, square batteries, flat batteries, coin-type batteries, button-type batteries, and the like.

[0113] FIG. 2 shows a non-aqueous electrolyte storage element 1 as an example of a square battery. Note that the figure is a perspective view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound with a separator interposed therebetween is housed in a square container 3. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0114] <Power storage device> The non-aqueous electrolyte energy storage device of this embodiment can be mounted as an energy storage unit (battery module) configured by aggregating a plurality of non-aqueous electrolyte energy storage devices in a power source for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), a power source for electronic devices such as personal computers and communication terminals, or a power source for power storage. In this case, the technology of the present invention may be applied to at least one non-aqueous electrolyte energy storage device included in the energy storage unit.

[0115] Fig. 3 shows an example of a power storage device 30 formed by further aggregating power storage units 20 in which two or more non-aqueous electrolyte energy storage devices 1 electrically connected are aggregated. The power storage device 30 may include a bus bar (not shown) for electrically connecting two or more non-aqueous electrolyte energy storage devices 1, a bus bar (not shown) for electrically connecting two or more power storage units 20, and the like. The power storage unit 20 or the power storage device 30 may include a state monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte energy storage devices.

[0116] <Method for manufacturing non-aqueous electrolyte energy storage device> The method for manufacturing the non-aqueous electrolyte energy storage device of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode body, preparing a non-aqueous electrolyte, and accommodating the electrode body and the non-aqueous electrolyte in a container. Preparing the electrode body includes preparing a positive electrode and a negative electrode, and forming the electrode body by laminating or winding the positive electrode and the negative electrode via a separator.

[0117] The method of accommodating the non-aqueous electrolyte in the container can be appropriately selected from known methods. For example, when a non-aqueous electrolyte solution is used as the non-aqueous electrolyte, the non-aqueous electrolyte solution may be injected through an injection port formed in the container and then the injection port may be sealed.

[0118] <Other embodiments> Furthermore, the positive electrode for the non-aqueous electrolyte storage element and the non-aqueous electrolyte storage element of the present invention are not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, a part of the configuration of one embodiment can be deleted. In addition, well-known technology can be added to the configuration of one embodiment.

[0119] In the above embodiment, the case where the non-aqueous electrolyte storage element is used as a rechargeable non-aqueous electrolyte secondary battery (for example, a lithium-ion secondary battery) has been described. However, the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries.

[0120] In the above embodiment, the electrode body in which the positive electrode and the negative electrode are laminated via a separator has been described. However, the electrode body may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state where a layer having no conductivity is formed on the active material layer of the positive electrode or the negative electrode.

Examples

[0121] Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to the following examples.

[0122] [Example 1] (Fabrication of positive electrode) A positive electrode mixture paste for forming a first active material layer is prepared using lithium nickel cobalt manganese composite oxide (hereinafter referred to as "NCM", average particle diameter 10 μm), which is a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure, acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a dispersion medium. The mass ratio of NCM, AB, and PVDF is 90:5:5 in terms of solid content. Manganese iron lithium phosphate (hereinafter referred to as "LMFP"), a polyanion compound having an olivine-type crystal structure, AB as a conductive agent, PVDF as a binder, and NMP as a dispersion medium are used to prepare a positive electrode mixture paste for forming a second active material layer. The mass ratio of LMFP, AB, and PVDF is 90:5:5 in terms of solid content. On an aluminum foil as a positive electrode substrate, the positive electrode mixture paste for forming the first active material layer and the positive electrode mixture paste for forming the second active material layer are coated in this order. Then, it is dried and roll-pressed. Thus, a positive electrode for a non-aqueous electrolyte storage element of Example 1 including a positive electrode substrate, a first active material layer, and a second active material layer in this order is obtained. The average thickness of the first active material layer is 10 μm, and the average thickness of the second active material layer is 100 μm.

[0123] [Example 2] A positive electrode for a non-aqueous electrolyte storage element of Example 2 is obtained by performing the same procedure as in Example 1 except that an aluminum foil provided with a carbon-coated layer on the surface is used as the positive electrode substrate.

[0124] [Comparative Example 1] A positive electrode for a non-aqueous electrolyte storage element of Comparative Example 1 in which a second active material layer is laminated on a positive electrode substrate is obtained by performing the same procedure as in Example 1 except that the first active material layer is not provided.

[0125] [Comparative Example 2] A positive electrode mixture paste is prepared using NCM, a lithium transition metal composite oxide having an α-NaFeO2-type crystal structure, LMFP, a polyanion compound having an olivine-type crystal structure, AB as a conductive agent, PVDF as a binder, and NMP as a dispersion medium. The mass ratio of NCM, LMFP, AB, and PVDF is 8:82:5:5 in terms of solid content. On an aluminum foil as a positive electrode substrate, the positive electrode mixture paste is coated. Then, it is dried and roll-pressed. Thus, a positive electrode for a non-aqueous electrolyte storage element of Comparative Example 2 in which a positive electrode active material layer containing NCM and LMFP is laminated on the positive electrode substrate is obtained. The average thickness of the positive electrode active material layer is 110 μm.

[0126] When comparing the positive electrodes for non-aqueous electrolyte storage elements of the examples and comparative examples, the following tendencies are presumed. In the positive electrode for a non-aqueous electrolyte storage element of Comparative Example 1 in which a second active material layer (positive electrode active material layer) mainly composed of LMFP is directly laminated on the positive electrode substrate, the adhesion between the positive electrode substrate and the positive electrode active material layer is low, and the energy density is not sufficient. In the positive electrode for a non-aqueous electrolyte storage element of Comparative Example 2 in which a positive electrode active material layer containing NCM and LMFP is laminated on the positive electrode substrate, the energy density is increased by using NCM compared to the positive electrode for a non-aqueous electrolyte storage element of Comparative Example 1, but the adhesion between the positive electrode substrate and the positive electrode active material layer is hardly improved. On the other hand, in the positive electrode for a non-aqueous electrolyte storage element of Example 1 in which a first active material layer mainly composed of NCM and a second active material layer mainly composed of LMFP are provided on the positive electrode substrate in this order, the first active material layer mainly composed of NCM provides sufficient adhesion between the positive electrode substrate and the positive electrode active material layer (the first active material layer and the second active material layer), and the energy density is also increased by using NCM. Further, in the positive electrode for a non-aqueous electrolyte storage element of Example 1, the average thickness of the second active material layer is larger than the average thickness of the first active material layer, and the content of the polyanion compound with respect to the total content of the lithium transition metal composite oxide and the polyanion compound is more than 50% by mass, so the thermal stability is also excellent. In the positive electrode for a non-aqueous electrolyte storage element of Example 2, the same advantages as those of the positive electrode for a non-aqueous electrolyte storage element of Example 1 can be obtained. The positive electrode for a non-aqueous electrolyte storage element of Example 1 uses an aluminum foil without a carbon coating layer as the positive electrode substrate, so it has the advantage that it can be manufactured at a lower cost and the energy density can be increased compared to the positive electrode for a non-aqueous electrolyte storage element of Example 2 using an aluminum foil with a carbon coating layer as the positive electrode substrate.

Industrial Applicability

[0127] The present invention can be applied to non-aqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles.

Explanation of Symbols

[0128] 1 Non-aqueous electrolyte storage element 2 Electrode body 3 Container 4 Positive electrode terminal 41 Positive electrode lead 5 Negative electrode terminal 51 Negative electrode lead 10 Positive electrode for non-aqueous electrolyte storage element 11 Base material 12 First active material layer 13 Second active material layer 20 Storage unit 30 Energy storage device

Claims

1. A base material, α-NaFeO ２ A first active material layer mainly composed of a lithium transition metal composite oxide having a crystal structure, and a second active material layer mainly composed of a polyanion compound having an olivine-type crystal structure, are provided in this order, a positive electrode for a non-aqueous electrolyte storage element, wherein an average thickness of the second active material layer is larger than an average thickness of the first active material layer.

2. A base material, α-NaFeO ２ A first active material layer mainly composed of a lithium transition metal composite oxide having a type crystal structure, and a second active material layer mainly composed of a polyanion compound having an olivine-type crystal structure, are provided in this order, a positive electrode for a non-aqueous electrolyte storage element, wherein a content of the polyanion compound with respect to a total content of the lithium transition metal composite oxide and the polyanion compound is more than 50% by mass.

3. The positive electrode for a non-aqueous electrolyte storage element according to claim 1 or claim 2, wherein the polyanion compound is lithium iron manganese phosphate.

4. The positive electrode for a non-aqueous electrolyte storage element according to claim 1 or claim 2, wherein the lithium transition metal composite oxide is a lithium nickel cobalt manganese composite oxide.

5. The positive electrode for a non-aqueous electrolyte storage element according to claim 1 or claim 2, wherein the average thickness of the first active material layer is 10% or less of the average thickness of the second active material layer.

6. The positive electrode for a non-aqueous electrolyte storage element according to claim 1 or claim 2, wherein an average particle diameter of the lithium transition metal composite oxide is 5 μm or more.

7. The base material has a metal layer, The positive electrode for a non-aqueous electrolyte storage element according to claim 1 or claim 2, wherein the first active material layer and the metal layer are directly laminated.

8. A non-aqueous electrolyte storage element including the positive electrode for a non-aqueous electrolyte storage element according to claim 1 or claim 2.

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