Electric energy storage element and electric energy storage device

Abstract

An electricity storage element according to one aspect of the present invention comprises: a positive electrode that comprises a positive electrode active material layer; a negative electrode; and a nonaqueous electrolyte. The positive electrode active material layer contains boron and aluminum; and the maximum voltage width, which is the difference between the charge upper limit voltage and the discharge lower limit voltage during normal use, is 1.1 V or less.

Description

Technical Field

[0001] The present invention relates to a power storage element and a power storage device.

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, etc. due to their high energy density. Generally, the non-aqueous electrolyte secondary battery 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 ions between both electrodes. Further, as power 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] For example, Patent Document 1 describes that by uniformly forming a coating of an oxide containing aluminum and boron on the surface of a positive electrode active material such as a lithium-containing composite oxide, the reaction between the positive electrode active material and the non-aqueous electrolyte solution is suppressed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a storage element, when charging and discharging are generally repeated (hereinafter, also referred to as "charge-discharge cycle"), it is known that due to various factors, the discharge capacity (hereinafter, also simply referred to as "capacity") decreases or the storage element bulges. On the other hand, in the storage element as described above, in order to increase the energy density, an expansion of the operating voltage range is required. However, the inventors of the present invention have found the following. That is, when the operating voltage range is expanded (that is, when the difference between the upper charge limit voltage and the lower discharge limit voltage is set large), the degree of expansion and contraction of the positive electrode active material particles included in the storage element due to charge and discharge increases. When the degree of expansion and contraction of the positive electrode active material particles increases, cracks are likely to occur in the positive electrode active material particles, and the current collection property of the positive electrode active material particles decreases. As a result, a decrease in capacity due to long-term charge-discharge cycles is likely to occur. Further, when cracks occur in the positive electrode active material particles, the positive electrode active material particles cannot contract, and the positive electrode active material layer expands. Therefore, the storage element itself is likely to bulge due to long-term charge-discharge cycles. As a result of intensive studies by the inventors of the present invention, it has been found that even the positive electrode active material proposed in the above-mentioned patent document does not necessarily obtain a sufficient effect depending on the operating voltage range. The present invention has been made based on the above circumstances, and an object of the present invention is to provide a storage element and a storage device in which swelling of the storage element is effectively improved in addition to a decrease in the capacity of the storage element due to long-term charge-discharge cycles.

Means for Solving the Problems

[0006] A storage element according to one aspect of the present invention includes a positive electrode including a positive electrode active material layer, a negative electrode, and a non-aqueous electrolyte. The positive electrode active material layer includes boron and aluminum, and a maximum voltage width, which is a difference between an upper charge limit voltage and a lower discharge limit voltage during normal use, is 1.1 V or less.

[0007] The power storage device according to another aspect of the present invention is a power storage device including a plurality of power storage elements, each of the plurality of power storage elements including a positive electrode including a positive electrode active material layer, a negative electrode, and a non-aqueous electrolyte, the positive electrode active material layer including boron and aluminum, and the plurality of power storage elements being controlled such that a maximum voltage width, which is a difference between a charge upper limit voltage and a discharge lower limit voltage during normal use, is 1.1 V or less.

Advantages of the Invention

[0008] According to the power storage element according to one aspect of the present invention and the power storage device according to another aspect of the present invention, it is possible to provide a power storage element and a power storage device in which, in addition to a decrease in the capacity of the power storage element due to long-term charge and discharge cycles, swelling of the power storage element is effectively improved.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0010] First, an overview of the power storage element disclosed by this specification will be described.

[0011] The power storage element according to one aspect of the present invention includes a positive electrode including a positive electrode active material layer, a negative electrode, and a non-aqueous electrolyte solution, the positive electrode active material layer including boron and aluminum, and a maximum voltage width, which is a difference between a charge upper limit voltage and a discharge lower limit voltage during normal use, is 1.1 V or less.

[0012] According to the energy storage element related to one aspect of the present invention, in addition to the reduction in the capacity of the energy storage element accompanying long-term charge-discharge cycles, an energy storage element in which the swelling of the energy storage element is effectively improved can be provided. The reason for this is not clear, but the following reasons are speculated. In conventional energy storage elements, attempts have been made to suppress the reaction between the positive electrode active material and the non-aqueous electrolyte (non-aqueous electrolyte solution), or to suppress the change in the crystal structure of the positive electrode active material accompanying charge-discharge cycles, in order to suppress the reduction in the capacity of the energy storage element accompanying charge-discharge cycles. However, when the operating voltage range is expanded, as described above, the degree of expansion of the positive electrode active material increases with charge and discharge. As the degree of expansion of the positive electrode active material increases, cracks and the like occur in the positive electrode active material, resulting in a decrease in the current collection property and expansion of the positive electrode active material particles, as well as expansion of the positive electrode active material layer, and a decrease in the capacity of the energy storage element and swelling of the energy storage element accompanying long-term charge-discharge cycles occur. On the other hand, according to the energy storage element related to one aspect of the present invention, since the positive electrode active material layer contains boron and aluminum and the maximum voltage width, which is the difference between the upper charge limit voltage and the lower discharge limit voltage during normal use, is set to 1.1 V or less, cracks and the like in the positive electrode active material are suppressed. Therefore, a decrease in the current collection property and expansion of the positive electrode active material particles, as well as expansion of the positive electrode active material layer, are suppressed, and in addition to the decrease in the capacity of the energy storage element accompanying long-term charge-discharge cycles, it is presumed that the swelling of the energy storage element is suppressed.

[0013] The positive electrode active material layer may include, as the positive electrode active material, a lithium transition metal composite oxide containing cobalt, manganese, and nickel, and the atomic ratio of nickel to the total of cobalt, manganese, and nickel in the lithium transition metal composite oxide may be 0.4 or more.

[0014] According to this energy storage element, in addition to the reduction in the capacity of the energy storage element accompanying long-term charge-discharge cycles, an energy storage element in which the swelling of the energy storage element is more effectively improved can be provided.

[0015] The power storage device according to another aspect of the present invention is a power storage device including a plurality of power storage elements, each of the plurality of power storage elements including a positive electrode including a positive electrode active material layer, a negative electrode, and a non-aqueous electrolyte, the positive electrode active material layer including boron and aluminum, and the plurality of power storage elements being controlled such that a maximum voltage width, which is a difference between a charging upper limit voltage and a discharging lower limit voltage during normal use, is 1.1 V or less.

[0016] According to the power storage device according to another aspect of the present invention, it is possible to provide a power storage device in which, in addition to a decrease in the capacity of the power storage element accompanying long-term charge and discharge cycles, swelling of the power storage element is effectively improved.

[0017] The configuration of the power storage element, the configuration of the power storage device, the method for manufacturing the power 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.

[0018] <Configuration of the power storage element> The power 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 that houses the electrode body and the non-aqueous electrolyte. The electrode body is usually a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked via a separator, or a wound type in which a positive electrode and a negative electrode are wound in a stacked state via a separator. The non-aqueous electrolyte exists in a state included in the positive electrode, the negative electrode, and the separator. As an example of the power storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as a "secondary battery") will be described.

[0019] (Positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed directly or via an intermediate layer on the positive electrode substrate.

[0020] The positive electrode substrate has conductivity. Whether it has "conductivity" is determined by the volume resistivity measured in accordance with JIS-H-0505 (1975) being 10 7It is determined with Ω·cm as the threshold. As the material of the positive electrode substrate, 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 corrosion resistance, high conductivity, and cost. Examples of the positive electrode substrate include a foil and a vapor deposition film, and a foil is preferable from the viewpoint of cost. Therefore, as the positive electrode substrate, an aluminum foil or an aluminum alloy foil is preferable. Examples of the aluminum or aluminum alloy include A1085, A3003, etc. defined in JIS-H-4000 (2014).

[0021] 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, it is possible to increase the strength of the positive electrode substrate and increase the energy density per volume of the secondary battery.

[0022] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited. For example, it contains a resin binder and conductive particles.

[0023] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer contains boron and aluminum. By making the positive electrode active material layer contain boron and aluminum and setting the maximum voltage width, which is the difference between the upper charge limit voltage and the lower discharge limit voltage during normal use, to 1.1 V or less as described later, in addition to the capacity reduction of the energy storage element accompanying long-term charge and discharge cycles, the swelling of the energy storage element can be effectively improved compared to the case where the positive electrode active material layer contains boron and aluminum and the maximum voltage width is greater than 1.1 V. The boron and aluminum contained in the positive electrode active material layer may be, for example, derived from the positive electrode active material or may not be derived from the positive electrode active material. Specifically, for example, if the positive electrode active material contains boron and / or aluminum, the positive electrode active material layer may be made to contain boron and / or aluminum. Also, the non-aqueous electrolyte contains a boron compound and / or an aluminum compound, and when the non-aqueous electrolyte penetrates into the positive electrode active material layer or when the non-aqueous electrolyte reacts with the positive electrode active material, the positive electrode active material layer may be made to contain boron and / or aluminum. Further, if the positive electrode active material layer contains a boron compound and / or an aluminum compound, the positive electrode active material layer may be made to contain boron and / or aluminum. The boron and aluminum contained in the positive electrode active material layer are preferably contained in the form of a boron compound and an aluminum compound, or a compound containing boron and aluminum. Examples of the boron compound include boron oxides such as boric acid and boron oxide, and compounds containing lithium and boron such as lithium tetrafluoroborate (LiBF 4 4), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalate borate (LiFOB), and the like. Examples of the aluminum compound include aluminum oxides such as aluminum oxide, aluminum hydroxides such as aluminum hydroxide, and compounds containing lithium and aluminum such as lithium hexafluoroaluminate. Also, the positive electrode active material layer may contain optional components such as a conductive agent, a binder, a thickener, and a filler as required.

[0024] The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium-ion secondary battery, a material that can occlude and release lithium ions is usually used. Examples of the positive electrode active material include, for example, α-NaFeO 2 -type lithium transition metal composite oxides having a crystal structure, spinel-type lithium transition metal composite oxides having a crystal structure, polyanion compounds, chalcogen compounds, sulfur, and the like. Examples of the α-NaFeO 2 -type lithium transition metal composite oxide include, for example, Li[Li x Ni (1-x) O 2 (0 ≦ x < 0.5), Li[Li x Ni γ Co (1-x-γ) O 2 (0 ≦ x < 0.5, 0 < γ < 1), Li[Li x Co (1-x) O 2 (0 ≦ x < 0.5), Li[Li x Ni γ Mn (1-x-γ) O 2 (0 ≦ x < 0.5, 0 < γ < 1), Li[Li x Ni γ Mn β Co (1-x-γ-β) O 2 (0 ≦ x < 0.5, 0 < γ, 0 < β, 0.5 < γ + β < 1), Li[Li x Ni γ Co β Al (1-x-γ-β) O 2 (0 ≦ x < 0.5, 0 < γ, 0 < β, 0.5 < γ + β < 1), etc. Examples of the spinel-type lithium transition metal composite oxide include Li x Mn 2 O 4 , Li x Ni γ Mn (2-γ) O 4 , etc. Examples of the polyanion compound include LiFePO 4 , LiMnPO 4 , LiNiPO 4 , LiCoPO 4 , Li3 V 2 (PO 4 ) 3 、 Li 2 MnSiO 4 、 Li 2 CoPO 4 F and the like can be mentioned. Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide and the like. Atoms or polyanions in these materials may be partially substituted with atoms or anion species composed of other elements. These materials may have their surfaces coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more of them may be mixed and used. The positive electrode active material may be a lithium transition metal composite oxide containing cobalt, manganese and nickel. In this case, the atomic ratio of nickel to the total of cobalt, manganese and nickel in the lithium transition metal composite oxide may be 0.4 or more, preferably 0.5 or more. When the atomic ratio of nickel to the total of cobalt, manganese and nickel is equal to or higher than the above lower limit (that is, when the ratio of nickel to cobalt, manganese and nickel is relatively high), the expansion and contraction of the positive electrode active material particles accompanying charge and discharge are larger than when it is less than the above lower limit, and there is a tendency that the capacity decrease and swelling of the power storage element accompanying long-term charge and discharge cycles become relatively large. Even when such a positive electrode active material is used, since the positive electrode active material layer contains boron and aluminum and the maximum voltage width during normal use is 1.1 V or less, in addition to the capacity decrease of the power storage element accompanying long-term charge and discharge cycles, the swelling of the power storage element can be more effectively suppressed.

[0025] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material particles is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material particles to be equal to or greater than the above lower limit, the production or handling of the positive electrode active material becomes easier. By setting the average particle size of the positive electrode active material to be equal to or less than the above upper limit, the electron conductivity of the positive electrode active material layer is improved. When a composite of the positive electrode active material and other materials is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. The "average particle size" conforms to JIS-Z-8825 (2013), and is based on the particle size distribution measured by the laser diffraction / scattering method for a dilution obtained by diluting the particles with a solvent, and is calculated in accordance with JIS-Z-8819-2 (2001). It means the value at which the volume-based cumulative distribution is 50%.

[0026] To obtain powder with a predetermined particle size, a crusher, a classifier, or the like is used. As the pulverization method, for example, 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, or a sieve can be mentioned. During pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. As the classification method, a sieve, an air classifier, or the like can be used as needed for both dry and wet processes.

[0027] The positive electrode active material particles may be composed of, for example, a central portion and a coating portion that coats at least a part of the central portion. In this case, boron and / or aluminum may be contained in the central portion of the positive electrode active material particles. By containing boron and / or aluminum in the central portion of the positive electrode active material particles, the capacity reduction of the energy storage element accompanying the charge / discharge cycle can be more effectively improved. The mechanism is not necessarily clear, but is presumed as follows. That is, when the charge / discharge cycle is repeated, cracks occur in the positive electrode active material particles, and new surfaces are formed on the surface of the positive electrode active material particles due to the cracks. On the new surfaces, the reaction between the positive electrode active material and the non-aqueous electrolyte is likely to occur, and it is presumed that the crystal structure of the positive electrode active material changes due to the reaction, resulting in a capacity reduction. By containing boron and / or aluminum in the central portion of the positive electrode active material particles, it is considered that the above-mentioned crystal structure change can be effectively suppressed.

[0028] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 98% by mass or less, and even more preferably 80% by mass or more and 95% by mass or less. 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 of the positive electrode active material layer.

[0029] The conductive agent is not particularly limited as long as it is a material having conductivity. Examples of such conductive agents include carbonaceous materials, metals, conductive ceramics, etc. Examples of carbonaceous materials include graphite, non-graphitic carbon, graphene-based carbon, etc. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, carbon black, etc. Examples of carbon black include furnace black, acetylene black, ketjen black, etc. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerenes, etc. Examples of the shape of the conductive agent include powder form, fibrous form, etc. As the conductive agent, one of these materials may be used alone, or two or more of them may be mixed and used. Also, these materials may be used in a composite form. For example, a material in which carbon black and CNT are composite may be used. Among these, carbon black is preferable from the viewpoints of electron conductivity and coatability, and among them, acetylene black is preferable.

[0030] The content of the conductive agent in the positive 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. By setting the content of the conductive agent within the above range, the energy density of the secondary battery can be increased.

[0031] 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, etc.

[0032] The content of the binder in the positive 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. By setting the content of the binder within the above range, the active material can be stably held.

[0033] 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.

[0034] 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.

[0035] The positive electrode active material layer may contain typical non-metal elements such as N, P, F, Cl, Br, and I, typical metal elements such as Li, Na, Mg, 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.

[0036] The positive electrode may include, in addition to the above-described positive electrode substrate and the positive electrode active material layer disposed directly or via an intermediate layer on the positive electrode substrate, an inorganic layer formed on the positive electrode active material layer. The inorganic layer may contain, for example, inorganic particles, fillers, and a binder. Note that, in this specification, the inorganic layer formed on the positive electrode active material layer as described above is not included in the positive electrode active material layer.

[0037] (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 can be selected from the configurations exemplified for the above positive electrode.

[0038] The negative electrode substrate has conductivity. As the material of the negative electrode substrate, metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof are used. Among these, copper or a copper alloy is preferable. Examples of the negative electrode substrate include a foil and a vapor deposition film, 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 and an electrolytic copper foil.

[0039] 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, the strength of the negative electrode substrate can be increased while increasing the energy density per unit volume of the secondary battery.

[0040] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as necessary. The optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified for the above positive electrode.

[0041] The negative electrode active material layer may contain, as components other than the negative electrode active material, conductive agent, binder, thickener, and filler, typical non-metallic elements such as B, N, P, F, Cl, Br, I, etc., typical metallic 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.

[0042] As the negative electrode active material, it can be appropriately selected from known negative electrode active materials. As the negative electrode active material for a lithium-ion secondary battery, a material that can occlude and release lithium ions is usually used. Examples of the negative electrode active material include metallic Li; metals or semi-metals such as Si and Sn; metal oxides or semi-metal oxides such as Si oxide, Ti oxide, and Sn oxide; Li 4 Ti 5 O 12 , LiTiO 2、 TiNb 2 O 7 and other titanium-containing oxides; 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, graphite and non-graphitic carbon are preferred. In the negative electrode active material layer, one of these materials may be used alone, or two or more of them may be mixed and used.

[0043] "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-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.

[0044] "Non-graphitic carbon" refers to the average lattice plane spacing (d 002refers to a carbon material having a d-spacing of 0.34 nm or more and 0.42 nm or less. Examples of non-graphitic carbon include non-graphitizable carbon and 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, and the like.

[0045] Here, the "discharged state" means a state in which the open-circuit voltage is 0.7 V or more in a single-pole battery using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic Li as the counter electrode. Since the potential of the metallic Li counter electrode in the open-circuit state is approximately equal to the oxidation-reduction potential of Li, the open-circuit voltage in the above single-pole battery is approximately equal to the potential of the negative electrode containing the carbon material with respect to the oxidation-reduction potential of Li. That is, the fact that the open-circuit voltage in the above single-pole battery is 0.7 V or more means that 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.

[0046] "Non-graphitizable carbon" refers to a carbon material having a d-spacing of 0.36 nm or more and 0.42 nm or less. 002 refers to a carbon material having a d-spacing of 0.36 nm or more and 0.42 nm or less.

[0047] "Graphitizable carbon" refers to a carbon material having a d-spacing of 0.34 nm or more and less than 0.36 nm. 002 refers to a carbon material having a d-spacing of 0.34 nm or more and less than 0.36 nm.

[0048] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material particles 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, the 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., the 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 particles to be equal to or greater than the above lower limit, the production or handling of the negative electrode active material becomes easier. By setting the average particle size of the negative electrode active material particles to be equal to or less than the above upper limit, the electron conductivity of the 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 positive electrode above. When the negative electrode active material is a metal such as metallic Li, the negative electrode active material may be in the form of a foil.

[0049] 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.

[0050] (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 in which a heat-resistant layer containing heat-resistant particles and a binder is 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 shut-down function, and polyimides, aramids, etc. are preferable from the viewpoint of oxidation decomposition resistance. As the base material layer of the separator, a material obtained by compounding these resins may also be used.

[0051] The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500 °C in an air atmosphere at 1 atm, and more preferably have a mass loss of 5% or less when heated from room temperature to 800 °C. Examples of materials with a mass loss of a predetermined amount or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; 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 and barium fluoride; covalent crystals such as silicon and diamond; and mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. 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, from the viewpoint of the safety of the energy storage element, silicon oxide, aluminum oxide, or aluminosilicate is preferable.

[0052] From the viewpoint of strength, the porosity of the separator is preferably 80% by volume or less, and from the viewpoint of discharge performance, it is preferably 20% by volume or more. Here, the "porosity" is a value based on volume and means the measured value by a mercury porosimeter.

[0053] 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, and polyvinylidene fluoride. 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 and a polymer gel may be used in combination.

[0054] (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.

[0055] 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, etc. As the non-aqueous solvent, those in which a part of the hydrogen atoms contained in these compounds are substituted with halogens may be used.

[0056] Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC is preferred.

[0057] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, etc. Among these, EMC is preferred.

[0058] 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, the dissociation of the electrolyte salt can be promoted and the ionic conductivity of the non-aqueous electrolyte can be improved. By using a chain carbonate, the viscosity of the non-aqueous electrolyte can be kept low. When 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.

[0059] As the electrolyte salt, it can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, etc. Among these, lithium salts are preferable.

[0060] Examples of the lithium salt include inorganic lithium salts such as LiPF 6 , LiPO 2 F 2 , LiBF 4 , LiClO 4 , LiN(SO 2 F) 2 , etc., and lithium salts having a halogenated hydrocarbon group such as LiSO 3 CF 3 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 C 2 F 5 ) 2 , LiN(SO 2 CF 3 )(SO 2 C 4 F 9 ), LiC(SO 2 CF 3 ) 3 , LiC(SO 2 C 2 F 5 ) 3 , etc. Among these, inorganic lithium salts are preferable, and LiPF 6 is more preferable.

[0061] The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / dm 3 or more and 2.5 mol / dm 3 or less at 20°C and 1 atm, more preferably 0.3 mol / dm 3 or more and 2.0 mol / dm 3 or less, even more preferably 0.5 mol / dm 3 or more and 1.7 mol / dm 3 or less, and particularly preferably 0.7 mol / dm 3 or more and 1.5 mol / dm 3 or less. By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0062] The non-aqueous electrolyte may contain an additive in addition to the non-aqueous solvent and the electrolyte salt. Examples of the additive include salts having an oxalic acid group such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis(oxalate)difluorophosphate (LiFOP); aromatic compounds such as biphenyl, alkyl biphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides 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; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, propene sultone, butane sultone, 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, 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.

[0063] As described above, in addition to including boron in the positive electrode active material layer by including boron in the positive electrode active material and including a boron compound in the positive electrode active material layer, boron may be included in the positive electrode active material layer by including a boron compound in the non-aqueous electrolyte. Specifically, boron may be included in the positive electrode active material layer by including a boron compound in the non-aqueous electrolyte solution. In that case, boron can be included in the positive electrode active material layer by including at least one of the above-described non-aqueous solvent, electrolyte salt, and additive containing boron. Examples of the electrolyte salt containing boron include, for example, LiBF 4 etc. Examples of the additive containing boron include lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiFOB), and the like. Whether or not the positive electrode active material layer contains boron and aluminum can be confirmed by ICP-MS (inductively coupled plasma mass spectrometer).

[0064] The content of the additive contained in the non-aqueous electrolyte solution 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, based on the mass of the entire non-aqueous electrolyte solution. 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.

[0065] A solid electrolyte may be used for the non-aqueous electrolyte, or a non-aqueous electrolyte solution and a solid electrolyte may be used in combination.

[0066] The solid electrolyte can be selected from any material having ion conductivity such as lithium, sodium, calcium, etc. and being solid at normal temperature (for example, 15°C to 25°C). Examples of the solid electrolyte include, for example, sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, polymer solid electrolytes, and the like.

[0067] Examples of the sulfide solid electrolyte in the case of a lithium-ion secondary battery include, for example, Li 2 S-P 2 S5 , LiI-Li 2 S-P 2 S 5 , Li 10 Ge-P 2 S 12 , etc. can be mentioned.

[0068] The shape of the energy storage element of this embodiment is not particularly limited, and examples include cylindrical batteries, rectangular batteries, flat batteries, coin-shaped batteries, button-shaped batteries, etc.

[0069] FIG. 1 shows an energy storage element 1 (non-aqueous electrolyte energy storage element) as an example of a rectangular 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 rectangular container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 51.

[0070] The energy storage element of this embodiment has a maximum voltage width, which is the difference between the upper charge limit voltage and the lower discharge limit voltage during normal use, of 1.1 V or less. Since the positive electrode active material layer contains boron and aluminum and the maximum voltage width during normal use is 1.1 V or less, in addition to the capacity reduction of the energy storage element accompanying long-term charge and discharge cycles, the swelling of the energy storage element can be effectively improved. Here, "during normal use" means the case where the energy storage element is used by adopting the charge and discharge conditions recommended or specified for the energy storage element, and when a charger is prepared for the energy storage element, it means the case where the energy storage element is used by applying the charger. In this specification, the oxidation reaction in which lithium ions etc. are released from the positive electrode active material is called "charging", and the reduction reaction in which lithium ions etc. are occluded in the positive electrode active material is called "discharging".

[0071] The maximum voltage width only needs to be 1.1 V or less, preferably 1.0 V or less, and more preferably 0.9 V or less. Although reducing the maximum voltage width will result in a decrease in the electrical energy that can be extracted in one charge and discharge cycle, it can more effectively improve the capacity reduction of the energy storage element and the swelling of the energy storage element associated with long-term charge and discharge cycles. Therefore, the same energy storage element can be used for a longer time, so the replacement frequency of the energy storage element can be reduced, and the maintenance cost can be reduced.

[0072] <Configuration of the energy storage device> An energy storage device according to another aspect of the present invention is an energy storage device including a plurality of energy storage elements, each of the plurality of energy storage elements including a positive electrode including a positive electrode active material layer, a negative electrode, and a non-aqueous electrolyte. The positive electrode active material layer contains boron and aluminum, and the plurality of energy storage elements are controlled so that the maximum voltage width, which is the difference between the upper limit voltage of charging and the lower limit voltage of discharging during normal use, is 1.1 V or less. Each of the plurality of energy storage elements can adopt the same configuration as the energy storage element according to an embodiment of the present invention described above.

[0073] The energy storage element of the present embodiment can be mounted as an energy storage device (energy storage module) configured by aggregating a plurality of energy storage elements 1 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.

[0074] FIG. 2 shows an example of an energy storage system 30 formed by further aggregating energy storage devices 20 formed by aggregating a plurality of electrically connected energy storage elements 1. The energy storage system 30 may include a bus bar (not shown) for electrically connecting a plurality of energy storage elements 1, a bus bar (not shown) for electrically connecting a plurality of energy storage devices 20, and the like. The energy storage device 20 or the energy storage system 30 may include a state monitoring device (not shown) for monitoring the states of a plurality of energy storage elements. In the power storage device 20, the maximum voltage width during normal use of the plurality of power storage elements 1 is controlled to be 1.1 V or less. The power storage device 20 may have a voltage control unit (not shown), and the maximum voltage width may be controlled to 1.1 V or less by the voltage control unit. The maximum voltage width only needs to be 1.1 V or less, preferably 1.0 V or less, and more preferably 0.9 V or less.

[0075] The method for controlling the maximum voltage width of the plurality of power storage elements 1 is not particularly limited. For example, the voltage of each of the plurality of power storage elements 1 included in the power storage device 20 may be controlled individually. Also, the maximum voltage width may be controlled by treating two or more power storage elements 1 as a group. Specifically, in the power storage device 20, the potential difference between the highest potential positive electrode terminal and the lowest potential negative electrode terminal of two or more power storage elements 1 connected in series may be controlled. In this case, the potential difference between the highest potential positive electrode terminal and the lowest potential negative electrode terminal is controlled to be equal to or less than the value obtained by multiplying the number of the plurality of power storage elements connected in series by 1.1 V. Note that the number of power storage elements 1 connected in series, which is the unit for controlling the voltage, is arbitrary. The method for controlling the voltage of the power storage element 1 is not particularly limited, and any method can be adopted.

[0076] Once a power storage device is configured by aggregating a plurality of power storage elements 1 (that is, when the plurality of power storage elements 1 are modularized), it is complicated to replace the power storage elements 1 that make up the power storage device, and in some cases, it is necessary to replace the power storage device as a whole. In the power storage device according to this embodiment, the capacity reduction of the power storage elements and the swelling of the power storage elements accompanying long-term charge and discharge cycles are more effectively improved. Therefore, the same power storage elements can be used for a longer time, so the replacement frequency of the power storage elements and the power storage device can be reduced, and the maintenance cost can be reduced.

[0077] <Method for manufacturing a power storage element> The manufacturing method of the energy storage element of the present 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 with a separator interposed therebetween.

[0078] 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, after injecting the non-aqueous electrolyte solution from an injection port formed in the container, the injection port may be sealed.

[0079] <Other Embodiments> Note that the energy storage element of the present invention is not limited to the above embodiment, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of another embodiment can be added to the configuration of a certain embodiment, and a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, a part of the configuration of a certain embodiment can be deleted. Also, well-known technology can be added to the configuration of a certain embodiment.

[0080] In the above embodiment, the case where the energy storage element is used as a non-aqueous electrolyte secondary battery (for example, a lithium-ion secondary battery) capable of charge and discharge has been described. However, the type, shape, dimensions, capacity, etc. of the energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double layer capacitors, or capacitors such as lithium ion capacitors.

[0081] In the above embodiment, the electrode body in which the positive electrode and the negative electrode are laminated with a separator interposed therebetween 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

[0082] Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited to the following examples.

[0083] [Example 1] (Production of positive electrode) Using a lithium transition metal composite oxide containing nickel, cobalt, and manganese as the positive electrode active material (the atomic ratio of nickel to the total of nickel, cobalt, and manganese is 0.5), an aluminum compound, a boron compound, acetylene black as the conductive agent, and polyvinylidene fluoride as the binder, a positive electrode mixture paste using N-methylpyrrolidone (NMP) as the dispersion medium was prepared. This positive electrode mixture paste was applied onto an aluminum foil which is the positive electrode substrate, and dried and pressed to produce a positive electrode having a positive electrode active material layer containing boron and aluminum formed thereon. An aluminum foil was provided with a positive electrode active material layer non-formation region where a part of the positive electrode active material layer was not formed. Note that boron and aluminum in the positive electrode active material layer are contained in the form of a boron compound and an aluminum compound, and the aluminum compound does not originate from the aluminum foil which is the positive electrode substrate. (Production of negative electrode) Using graphite as the negative electrode active material, a negative electrode having a negative electrode active material layer formed thereon was produced on a copper foil which is the negative electrode substrate. The copper foil was provided with a negative electrode active material layer non-formation region where a part of the negative electrode active material layer was not formed. (Preparation of separator) A polyethylene microporous membrane was prepared as the separator. (Preparation of non-aqueous electrolyte) LiPF 3 was dissolved in a solvent obtained by mixing ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) so that the salt concentration became 1.0 mol / dm 6 to prepare a non-aqueous electrolyte. (Production of power storage element) The positive electrode, negative electrode, and separator obtained by the above procedure were laminated and wound to obtain a wound electrode body. Thereafter, a positive electrode lead was joined to the non-active material layer forming region of the positive electrode, and a negative electrode lead was joined to the non-active material layer forming region of the negative electrode. Thereafter, the electrode body was enclosed in a metallic rectangular container, the above-described non-aqueous electrolyte was injected into the container, and the container was sealed to obtain an electrical storage element. The maximum thickness of the electrical storage element in the direction in which the positive electrode, negative electrode, and separator were laminated was 34 mm. [Evaluation] (Measurement of initial discharge capacity) Regarding the obtained electrical storage element, the initial discharge capacity was measured under the following conditions. First, the electrical storage element was charged at a constant current of 1C up to 4.25V at 25°C, and then constant voltage charging was performed at 4.25V with the condition that the current becomes 0.01C as the end condition. Thereafter, a 10-minute rest period was provided, and after the rest period elapsed, discharge was performed at a constant current of 0.33C until the cut-off voltage of 2.75V at 25°C, and the discharge capacity at that time was defined as the initial discharge capacity. (Capacity retention rate after charge-discharge cycles) After measuring the initial discharge capacity, a charge-discharge cycle test was performed at a temperature of 45°C. Specifically, constant current charging was performed at a charging current of 1C up to 4.25V, and then constant voltage charging was performed at 4.25V with the condition that the current becomes 0.01C as the end condition. After the constant voltage charging ended, a 10-minute rest period was provided, and after the rest period elapsed, constant current discharge was performed at a discharge current of 1C until the cut-off voltage of 3.51V. After the constant current discharge ended, a 10-minute rest period was provided. The above charge-discharge was defined as one cycle, and charge-discharge was performed for several hundred to several thousand cycles. Every several hundred cycles, the discharge capacity and the maximum thickness of the electrical storage element in the direction in which the positive electrode, negative electrode, and separator were laminated were confirmed under the same conditions as the initial discharge capacity. The ratio (percentage) of the discharge capacity after the charge-discharge cycle to the initial discharge capacity was defined as the capacity retention rate (%), and the above charge-discharge cycle was continued until the capacity retention rate became 80% or less, and the number of cycles at which the capacity retention rate reached 80% was calculated by interpolation. Also, the number of cycles at which the maximum thickness of the electrical storage element reached 40 mm was calculated by interpolation.

[0084] [Example 2, Comparative Examples 1 to 10] Except that the presence or absence of boron and aluminum in the positive electrode active material layer and the maximum voltage width (the difference between the voltage during constant voltage charging and the end voltage of constant current discharging) were as described in Tables 1 to 3, a power storage element was fabricated by the same procedure as in Example 1, and the initial discharge capacity was measured and a charge-discharge cycle test was conducted. The maximum voltage width was changed by changing the end voltage of constant current discharging. (Improvement rate of capacity retention and thickness) The improvement rate of the capacity retention with respect to the reference test example (hereinafter, also simply referred to as "improvement rate of capacity retention") was calculated based on the following formula. Improvement rate of capacity retention (%) = (number of cycles at which the capacity retention of each test example reaches 80%) ÷ (number of cycles at which the capacity retention of the reference test example reaches 80%) × 100 - 100 Improvement rate of thickness (%) = (number of cycles at which the maximum thickness of the power storage element of each test example reaches 40 mm) ÷ (number of cycles at which the maximum thickness of the power storage element of the reference test example reaches 40 mm) × 100 - 100

[0085] The presence or absence of boron and aluminum in the positive electrode active material layer, the maximum voltage width, the number of cycles at which the capacity retention reaches 80%, the improvement rate of the capacity retention, the number of cycles at which the thickness reaches 40 mm, and the improvement rate of the thickness of Examples 1 and 2 and Comparative Examples 1 to 10 are shown in Tables 1 to 3.

[0086]

Table 1

[0087] According to Table 1, when the maximum voltage width is 1.1 V or less (0.74 V), for the capacity retention rate, based on Comparative Example 1 in which the positive electrode active material layer contains neither boron nor aluminum, the improvement rate of Comparative Example 2 containing only boron was 182%, and the improvement rate of Comparative Example 3 containing only aluminum was 6%. In contrast, the improvement rate of Example 1 containing both boron and aluminum was 229%, indicating that the capacity retention rate was unexpectedly improved. Regarding the maximum thickness of the power storage element, based on Comparative Example 1 in which the positive electrode active material layer contains neither boron nor aluminum, the improvement rate of Comparative Example 2 containing only boron was 46%, and the improvement rate of Comparative Example 3 containing only aluminum was 10%. In contrast, the improvement rate of Example 1 containing both boron and aluminum was 76%, indicating that the swelling of the power storage element was unexpectedly improved.

[0088]

Table 2

[0089] According to Table 2, when the maximum voltage width is 1.1 V or less (0.84 V), for the capacity retention rate, based on Comparative Example 4 in which the positive electrode active material layer contains neither boron nor aluminum, the improvement rate of Comparative Example 5 containing only boron was 280%, and the improvement rate of Comparative Example 6 containing only aluminum was 8%. In contrast, in Example 2 containing both boron and aluminum, the improvement rate was 346%, indicating that the capacity retention rate was unexpectedly improved. Regarding the maximum thickness of the power storage element, based on Comparative Example 4 in which the positive electrode active material layer contains neither boron nor aluminum, the improvement rate of Comparative Example 5 containing only boron was 79%, and the improvement rate of Comparative Example 6 containing only aluminum was 7%. In contrast, in Example 2 containing both boron and aluminum, the improvement rate was 100%, indicating that the swelling of the power storage element was unexpectedly improved.

[0090]

Table 3

[0091] On the other hand, according to Table 3, when the maximum voltage width is 1.5V, which is greater than 1.1V, regarding the capacitance retention rate, based on Comparative Example 7 in which the positive electrode active material layer contains neither boron nor aluminum, the improvement rate of Comparative Example 8 containing only boron is 202%, and the improvement rate of Comparative Example 9 containing only aluminum is -1%. In contrast, the improvement rate of Comparative Example 10 containing both boron and aluminum is 208%. It can be seen that there is no significant difference from the improvement rates expected from the cases of containing only boron (Comparative Example 8) and containing only aluminum (Comparative Example 9). Regarding the maximum thickness of the energy storage element as well, based on Comparative Example 7 in which the positive electrode active material layer contains neither boron nor aluminum, the improvement rate of Comparative Example 8 containing only boron is 109%, and the improvement rate of Comparative Example 9 containing only aluminum is 0%. In contrast, the improvement rate of Comparative Example 10 containing both boron and aluminum is 118%. No significant difference was observed from the improvement rates expected from the cases of containing only boron (Comparative Example 8) and containing only aluminum (Comparative Example 9).

[0092] For reference, Table 4 shows the discharge capacity retention rate and the maximum thickness of the energy storage element after performing 1000 charge-discharge cycle tests in Example 1 and Comparative Example 2.

[0093]

Table 4

[0094] After performing 1000 charge-discharge cycle tests, there was almost no change in the capacitance retention rate and the maximum thickness of the energy storage element between Example 1 in which the positive electrode active material layer contains boron and aluminum and Comparative Example 2 in which the positive electrode active material layer contains only boron. Therefore, it can be said that the energy storage element according to one aspect of the present invention exhibits a remarkable effect of being able to suppress the accompanying decrease in capacitance and the swelling of the energy storage element when performing a long-term charge-discharge cycle of several thousand cycles.

[0095] As described above, when the positive electrode active material layer contains boron and aluminum and the maximum potential width is 1.1 V or less, it has been shown that in addition to the decrease in the capacity of the power storage element accompanying long-term charge and discharge cycles, the swelling of the power storage element is effectively improved.

[0096] The present invention is suitably used as a power storage element used as a power source for electronic devices such as personal computers and communication terminals, and automobiles. In particular, it is suitably used for power storage that is difficult to replace once installed, maintains a high capacity over a long period of time, and has a high need to suppress the swelling of the power storage element.

Explanation of Signs

[0097] 1 Power storage element 2 Electrode body 3 Container 4 Positive electrode terminal 41 Positive electrode lead 5 Negative electrode terminal 51 Negative electrode lead 20 Power storage device 30 Power storage system

Claims

1. A positive electrode including a positive electrode active material layer, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode active material layer includes a positive electrode active material, a boron compound, and an aluminum compound, the positive electrode active material is a lithium transition metal composite oxide containing cobalt, manganese, and nickel, and having an atomic ratio of nickel to the total of cobalt, manganese, and nickel of 0.5 or more, the boron compound is a boron oxide or a compound containing lithium and boron, the aluminum compound is an aluminum oxide, an aluminum hydroxide, or a compound containing lithium and aluminum, the negative electrode includes a carbon material as a negative electrode active material, and a maximum voltage width, which is a difference between a charging upper limit voltage and a discharging lower limit voltage during normal use, is 1.0 V or less, a power storage element.

2. The power storage element according to Claim 1, wherein the maximum voltage width is 0.9 V or less.

3. A power storage device including a plurality of power storage elements, wherein each of the plurality of power storage elements includes a positive electrode including a positive electrode active material layer, a negative electrode, and a non-aqueous electrolyte, the positive electrode active material layer includes a positive electrode active material, a boron compound, and an aluminum compound, the positive electrode active material is a lithium transition metal composite oxide containing cobalt, manganese, and nickel, and having an atomic ratio of nickel to the total of cobalt, manganese, and nickel of 0.5 or more, the boron compound is a boron oxide or a compound containing lithium and boron, the aluminum compound is an aluminum oxide, an aluminum hydroxide, or a compound containing lithium and aluminum, the negative electrode includes a carbon material as a negative electrode active material, and the plurality of power storage elements are controlled such that a maximum voltage width, which is a difference between a charging upper limit voltage and a discharging lower limit voltage during normal use, is 1.0 V or less, a power storage device.

4. The power storage device according to Claim 3, wherein the plurality of power storage elements are controlled such that the maximum voltage width is 0.9 V or less.

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