Non-aqueous alkali metal storage element

Abstract

To provide a nonaqueous alkali metal power storage element, suppressing increase in resistance in high-temperature high-voltage cycles and having a high capacity retention rate.SOLUTION: There is provided, a nonaqueous alkali metal power storage element including an electrode body comprising a positive electrode, a negative electrode and a separator, and a nonaqueous electrolytic solution containing alkali metal ions. A positive electrode active material layer contains: a positive electrode active material containing a carbon material; and an alkali metal carbonate. Concentration of hexafluorophosphate ions contained in the nonaqueous electrolytic solution is 0.00 mol / L or more and 0.05 mol / L or less. The positive electrode has a protective layer and a non-protective layer, on a positive electrode current collector. On a projection plane, in a lamination direction, of the electrode body, the protective layer overlaps a negative electrode end. When A(mAh / g) represents alkali metal ion concentration per unit area at an outer periphery of the negative electrode, and B (mAh / g) represents alkali metal ion concentration per unit area at a central part of the negative electrode, 1.02≤B / A≤1.45 is satisfied.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a non-aqueous alkali metal storage element.

Background Art

[0002] In recent years, from the viewpoints of global environmental conservation and effective use of energy aiming at resource saving, power smoothing systems for wind power generation or late-night power storage systems, home-use distributed power storage systems based on solar power generation technology, power storage systems for electric vehicles, etc. have attracted attention. The first requirement for the batteries used in these power storage systems is high energy density. As a promising candidate for a high energy density battery capable of meeting such requirements, the development of lithium-ion secondary batteries has been vigorously promoted. The second requirement is high output characteristics. For example, in a combination of a high-efficiency engine and a power storage system (e.g., a hybrid electric vehicle) or a combination of a fuel cell and a power storage system (e.g., a fuel cell electric vehicle), a power storage system that exhibits high output discharge characteristics during acceleration is required. Currently, as high-output power storage devices, electric double layer capacitors, nickel-metal hydride batteries, etc. have been developed.

[0003] Among electric double layer capacitors, those using activated carbon for the electrodes have output characteristics of about 0.5 to 1 kW / L. This electric double layer capacitor has not only high output characteristics but also high durability (cycle characteristics and high-temperature storage characteristics), and has been considered to be an optimal device in the fields where the above high output is required. However, since its energy density is only about 1 to 5 Wh / L, further improvement in energy density is necessary.

[0004] The nickel-metal hydride battery generally adopted in hybrid electric vehicles at present has a high output equivalent to that of an electric double layer capacitor and has an energy density of about 160 Wh / L. However, research is being vigorously promoted to further increase its energy density and output characteristics and to improve its durability (especially stability at high temperatures).

[0005] Even in lithium-ion secondary batteries, research is underway to increase the output. For example, a lithium-ion secondary battery has been developed that can achieve an output higher than 3 kW / L at a depth of discharge (i.e., the ratio (%) of the discharge amount to the discharge capacity of the energy storage element) of 50%. However, its energy density is 100 Wh / L or less, which is a design that deliberately suppresses the high energy density, which is the greatest characteristic of lithium-ion secondary batteries. In addition, its durability (cycle characteristics and high-temperature storage characteristics) is inferior to that of electric double-layer capacitors. Therefore, such lithium-ion secondary batteries are used in a narrower range than the range of 0 to 100% depth of discharge in order to have practical durability. Since the capacity of the lithium-ion secondary battery that can actually be used becomes even smaller, research to further improve the durability is being vigorously carried out.

[0006] As described above, there is a strong demand for the practical application of an energy storage element that combines high energy density, high output characteristics, and high durability. However, since the existing energy storage elements described above have their own advantages and disadvantages, a new energy storage element that meets these technical requirements is required. As a promising candidate, an energy storage element called a lithium-ion capacitor has attracted attention and is being actively developed. A lithium-ion capacitor is a type of energy storage element that uses a non-aqueous electrolyte containing a lithium salt (hereinafter also referred to as a "non-aqueous alkali metal energy storage element"). In the positive electrode, a non-Faradaic reaction occurs due to the adsorption and desorption of anions similar to that of an electric double-layer capacitor at about 3 V or higher, and in the negative electrode, charge and discharge are performed by a Faradaic reaction due to the insertion and release of lithium ions similar to that of a lithium-ion secondary battery.

[0007] Summarizing the electrode materials commonly used in the above-mentioned energy storage elements and their characteristics, generally, when materials such as activated carbon are used for the electrodes and charge and discharge are performed by adsorption and desorption of ions on the surface of the activated carbon (non-Faradaic reaction), high power and high durability can be obtained, but the energy density becomes low (for example, it is doubled). On the other hand, when an oxide or a carbon material is used for the electrodes and charge and discharge are performed by a Faradaic reaction, the energy density becomes high (for example, it is 10 times that of the non-Faradaic reaction using activated carbon), but there are problems with durability and output characteristics.

[0008] As a combination of these electrode materials, an electric double layer capacitor is characterized in that activated carbon (energy density 1 times) is used for the positive and negative electrodes, and charge and discharge are performed by non-Faradaic reactions on both the positive and negative electrodes. Therefore, it has high power and high durability, but has the characteristic of low energy density (positive electrode 1 times × negative electrode 1 times = 1).

[0009] A lithium ion secondary battery is characterized in that a lithium transition metal oxide (energy density 10 times) is used for the positive electrode and a carbon material (energy density 10 times) is used for the negative electrode, and charge and discharge are performed by Faradaic reactions on both the positive and negative electrodes. Therefore, it has a high energy density (positive electrode 10 times × negative electrode 10 times = 100), but there are problems with output characteristics and durability. Furthermore, in order to satisfy the high durability required in hybrid electric vehicles and the like, the depth of discharge must be limited, and in a lithium ion secondary battery, only 10 to 50% of its energy can be used.

[0010] A lithium ion capacitor is characterized in that activated carbon (energy density 1 times) is used for the positive electrode and a carbon material (energy density 10 times) is used for the negative electrode, and charge and discharge are performed by a non-Faradaic reaction at the positive electrode and a Faradaic reaction at the negative electrode. Therefore, it is an asymmetric capacitor that combines the characteristics of an electric double layer capacitor and a lithium ion secondary battery. The lithium ion capacitor has high power and high durability, while having a high energy density (positive electrode 1 times × negative electrode 10 times = 10), and is characterized by not requiring limitation of the depth of discharge like a lithium ion secondary battery.

[0011] Regarding further improvement of the reliability and high-temperature durability of the above lithium-ion capacitor, various studies have been conducted (Patent Documents 1 to 4). Patent Documents 1 and 2 disclose a lithium-ion secondary battery provided with an insulating tape attached (Patent Document 1) or a coated insulating material layer (Patent Document 2) to prevent short circuit between the positive electrode and the negative electrode. Patent Document 3 discloses a technique for suppressing corrosion of a current collector by a protective layer containing AlF3 on the surface of an aluminum current collector. Patent Document 4 discloses a non-aqueous lithium storage element that suppresses corrosion of an aluminum foil in a high-voltage environment and has high durability against storage in a high-temperature environment of 85°C or higher.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0013]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0014] However, none of the documents consider at all the corrosion of the positive electrode current collector caused by the in-plane potential variation of the electrode in high-temperature and high-voltage cycles, and the occurrence of side reactions with the excess electrolytic solution inside the cell at the negative electrode end. Furthermore, the suppression of both the deactivation of the alkali metal ions doped in the negative electrode in a high-temperature environment and the accompanying decrease in the capacity retention rate is not considered.

[0015] In view of the above situation, the problem to be solved by the present invention is to provide a non-aqueous alkali metal storage element that suppresses the increase in resistance in high-temperature and high-voltage cycles and has a high capacity retention rate.

Means for Solving the Problem

[0016] The above problems are solved by the following technical means. That is, the present invention is as follows. [1] A non-aqueous alkali metal storage element including a positive electrode including a positive electrode active material layer disposed on a positive electrode current collector, a negative electrode including a negative electrode active material layer disposed on a negative electrode current collector, and a separator, and a non-aqueous electrolytic solution containing alkali metal ions, wherein the positive electrode active material layer includes a positive electrode active material containing a carbon material and an alkali metal carbonate, the concentration of hexafluorophosphate ions contained in the non-aqueous electrolytic solution is 0.00 mol / L or more and 0.05 mol / L or less, the positive electrode has a protective layer and a non-protective layer on the positive electrode current collector, and in the projection plane in the stacking direction of the electrode body, the protective layer and the negative electrode end overlap, and when the alkali metal ion concentration per unit area of the outer peripheral portion of the negative electrode is A (mAh / g) and the alkali metal ion concentration per unit area of the central portion is B (mAh / g), 1.02 ≦ B / A ≦ 1.45. [2] The non-aqueous alkali metal storage element according to item 1, wherein the protective layer exists on both surfaces of the positive electrode. [3] The negative electrode has the negative electrode active material layer on both sides of the negative electrode current collector, the outermost layer of the electrode body is the negative electrode, and when the alkali metal ion concentration per unit area at the center of the negative electrode active material layer that is not opposed to the positive electrode is E (mAh / g), B > E. The non-aqueous alkali metal storage element according to item 1 or 2. [4] The protective layer is a protective tape, and the base material of the protective tape is at least one material selected from the group consisting of polyether ketone, polyphenylene sulfide, polyethylene terephthalate, polyethylene naphthalate, polyamide, polyimide, aramid, acetate cloth, and polytetrafluoroethylene tape. The non-aqueous alkali metal storage element according to any one of items 1 to 3. [5] The protective layer contains at least one carbon material selected from the group consisting of carbon black, graphite, graphene, and carbon nanotubes. The non-aqueous alkali metal storage element according to any one of items 1 to 4. [6] The protective layer contains inorganic fine particles. The non-aqueous alkali metal storage element according to any one of items 1 to 5. [7] The positive electrode and / or the negative electrode contains carbon nanotubes. The non-aqueous alkali metal storage element according to any one of items 1 to 6. [8] A power storage module including the non-aqueous alkali metal storage element according to any one of items 1 to 7. [9] The above power storage module is incorporated into at least one system selected from the group consisting of a power regeneration assist system, a power load leveling system, an uninterruptible power supply system, a non-contact power supply system, an energy harvesting system, a power storage system, a solar power generation power storage system, an electric power steering system, an emergency power supply system, an in-wheel motor system, an idle stop system, an electric vehicle, a plug-in hybrid vehicle, a hybrid vehicle, an electric motorcycle, a rapid charging system, and a smart grid system. The power storage module according to item 8.

[10] The non-aqueous alkali metal power storage element according to any one of Items 1 to 7, and a lead battery, a nickel-hydrogen battery, a lithium-ion secondary battery, or a fuel cell connected in series or parallel to form a power storage system.

Advantages of the Invention

[0017] According to the present invention, in a high-temperature and high-voltage cycle, corrosion of the positive electrode current collector and side reactions at the negative electrode end are suppressed, so that the rate of increase in resistance is small, and inactivation of alkali metal ions in the negative electrode is suppressed, thereby providing a non-aqueous alkali metal power storage element with a high capacity retention rate.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention (hereinafter referred to as "the present embodiments") will be described in detail, but the present invention is not limited to the present embodiments. The upper limit value and the lower limit value in each numerical range of the present embodiments can be arbitrarily combined to form an arbitrary numerical range.

[0020] 《Non-aqueous alkali metal power storage element》 The non-aqueous alkali metal power storage element of the present embodiment mainly includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. As the non-aqueous electrolyte, a solution in which alkali metal ions are dissolved in an organic solvent is used.

[0021] 〈Negative electrode〉 The negative electrode in this embodiment has a negative electrode current collector and a negative electrode active material layer provided on one or both sides thereof.

[0022] [Negative electrode active material layer] The negative electrode active material layer contains a negative electrode active material, and may optionally contain arbitrary components such as a dispersant, a conductive filler, and a binder, among others.

[0023] (Negative electrode active material) As the negative electrode active material, a material capable of occluding and releasing alkali metal ions can be used. Specifically, examples include carbon materials, titanium oxides, silicon, silicon oxides, silicon alloys, silicon compounds, tin, and tin compounds. The content of the negative electrode active material in the negative electrode active material layer of the negative electrode precursor is preferably 70% by mass or more, more preferably 80% by mass or more, based on the total mass of the negative electrode active material layer. The negative electrode active material is preferably in particulate form.

[0024] The negative electrode active material preferably contains a carbon material. The content rate of the carbon material with respect to the total amount of the negative electrode active material is preferably 50% by mass or more, more preferably 70% by mass or more. The content rate of the carbon material can be 100% by mass, but from the viewpoint of favorably obtaining the effects of using other materials in combination, for example, it is preferably 95% by mass or less, and may be 90% by mass or less. The upper and lower limits of the range of the content rate of the carbon material can be arbitrarily combined.

[0025] Examples of the carbon material include non-graphitizable carbon materials; graphitizable carbon materials; carbon black; carbon nanoparticles; activated carbon; artificial graphite; natural graphite; graphitized mesophase carbon microspheres; graphite whiskers; amorphous carbonaceous materials such as polyacene-based substances; carbonaceous materials obtained by heat-treating carbon precursors such as petroleum-based pitch, coal-based pitch, mesocarbon microbeads, coke, and synthetic resins (e.g., phenol resins, etc.); thermal decomposition products of furfuryl alcohol resins or novolak resins; fullerenes; carbon nanofibers; and composite carbon materials thereof.

[0026] Among these, from the viewpoint of reducing the resistance of the negative electrode, one or more graphite materials selected from artificial graphite, natural graphite, graphitized mesophase carbon microspheres, graphite whiskers, and high specific surface area graphite, etc.; and one or more carbonaceous material precursors selected from petroleum pitch, coal pitch, mesocarbon microbeads, coke, and synthetic resins such as phenolic resin, etc. are heat-treated in a coexisting state to obtain a composite carbon material in which the graphite material and the carbonaceous material derived from the carbonaceous material precursor are combined. The carbonaceous material precursor is not particularly limited as long as it becomes a carbonaceous material by heat treatment, but petroleum pitch or coal pitch is particularly preferred. Before heat treatment, the graphite material and the carbonaceous material precursor may be mixed at a temperature higher than the melting point of the carbonaceous material precursor. The heat treatment temperature may be a temperature at which the components generated by the volatilization or thermal decomposition of the carbonaceous material precursor used become a carbonaceous material, but is preferably 400 °C or higher and 2,500 °C or lower, more preferably 500 °C or higher and 2,000 °C or lower, and still more preferably 550 °C or higher and 1,500 °C or lower. The atmosphere for heat treatment is not particularly limited, but a non-oxidizing atmosphere is preferred.

[0027] The BET specific surface area of the composite carbon material is preferably 1 m 2 / g or more and 50 m 2 / g or less, more preferably 1.5 m 2 / g or more and 40 m 2 / g or less, still more preferably 2 m 2 / g or more and 25 m 2 / g or less. If the BET specific surface area of the composite carbon material is 1 m 2 / g or more, a sufficient number of reaction sites with lithium ions in the non-aqueous electrolyte can be ensured, so that high input / output characteristics can be exhibited. If the BET specific surface area of the composite carbon material is 50 m 2 / g or less, the charge / discharge efficiency of lithium ions is improved, and the reduction decomposition of the non-aqueous electrolyte during charge / discharge is suppressed, so that high high-load charge / discharge cycle characteristics can be exhibited.

[0028] The average pore diameter of the composite carbon material is preferably 1.5 nm or more and 25 nm or less, more preferably 2 nm or more and 22 nm or less, still more preferably 3 nm or more and 20 nm or less, and particularly preferably 3.5 nm or more and 18 nm or less. When the average pore diameter of the composite carbon material is 1.5 nm or more, there are many pores larger than the size of the solvated alkali metal ions (1.2 nm or less) in the non-aqueous electrolyte, so the diffusion of the solvated alkali metal ions in the composite carbon material is good, and the non-aqueous alkali metal storage element using this can exhibit high input / output characteristics. On the other hand, when the average pore diameter of the composite carbon material is 25 nm or less, the bulk density of the negative electrode active material layer using this can be sufficiently improved, so it can exhibit a high energy density.

[0029] The composite carbon material may be in particulate form, and its average particle diameter is preferably 1 μm or more and 10 μm or less, more preferably 2 μm or more and 8 μm or less, still more preferably 3 μm or more and 6 μm or less. When the average particle diameter of the composite carbon material is 1 μm or more, the charge / discharge efficiency of the alkali metal ions can be improved, so it can exhibit high high-load charge / discharge cycle characteristics. When the average particle diameter of the composite carbon material is 10 μm or less, the reaction sites with the alkali metal ions in the non-aqueous electrolyte increase, so it can exhibit high input / output characteristics.

[0030] The mass ratio of the carbonaceous material to the graphite material in the composite carbon material is preferably 1 mass% or more and 20 mass% or less, more preferably 1.2 mass% or more and 15 mass% or less, still more preferably 1.5 mass% or more and 10 mass% or less, and even more preferably 2 mass% or more and 5 mass% or less. When the mass ratio of the carbonaceous material is 1 mass% or more, the carbonaceous material can sufficiently increase the reaction sites with the alkali metal ions in the non-aqueous electrolyte, and the desolvation of the alkali metal ions also becomes easy, so it can exhibit high input / output characteristics. When the mass ratio of the carbonaceous material is 20 mass% or less, the solid-state diffusion of the alkali metal ions between the carbonaceous material and the graphite material can be kept good, so it can exhibit high input / output characteristics. Also, since the charge / discharge efficiency of the alkali metal ions can be improved, it can exhibit high high-load charge / discharge cycle characteristics.

[0031] The doping amount of alkali metal ions per unit mass of the composite carbon material is preferably 50 mAh / g or more and 700 mAh / g or less, more preferably 70 mAh / g or more and 650 mAh / g or less, still more preferably 90 mAh / g or more and 600 mAh / g or less, and even more preferably 100 mAh / g or more and 550 mAh / g or less. By doping alkali metal ions, the negative electrode potential becomes lower. Therefore, when a negative electrode containing a composite carbon material doped with alkali metal ions is combined with a positive electrode, the voltage of the non-aqueous alkali metal storage element increases, and the utilization capacity of the positive electrode increases. As a result, the capacity and energy density of the obtained non-aqueous alkali metal storage element increase. If the doping amount of alkali metal ions per unit mass of the composite carbon material is 50 mAh / g or more, alkali metal ions are well doped even in irreversible sites where alkali metal ions once inserted into the composite carbon material cannot be desorbed, so a high energy density can be obtained. The more the doping amount, the lower the negative electrode potential, and the input / output characteristics, energy density, and durability are improved. If the doping amount of alkali metal ions per unit mass of the composite carbon material is 700 mAh / g or less, side effects such as precipitation of alkali metals such as lithium metal are less likely to occur.

[0032] The BET specific surface area of the graphite material used for the composite carbon material is preferably 0.5 m 2 / g or more and 80 m 2 / g or less, more preferably 1 m 2 / g or more and 70 m 2 / g or less, still more preferably 1.5 m 2 / g or more and 60 m 2 / g or less. If the BET specific surface area of the graphite material used for the composite carbon material is within the above range, the BET specific surface area of the composite carbon material can be adjusted to the range described above.

[0033] The graphite material used in the composite carbon material may be in particulate form, and its average particle size is preferably 1 μm or more and 10 μm or less, more preferably 2 μm or more and 8 μm or less. If the average particle size of the graphite material used in the composite carbon material is within the range of 1 μm or more and 10 μm or less, the average particle size of the composite carbon material can be adjusted to the range described above.

[0034] The carbonaceous material precursor used as a raw material for the composite carbon material is a solid, liquid, or organic material soluble in a solvent that can be combined with a graphite material by heat treatment to form a composite carbon material. Examples of such carbonaceous material precursors include pitch, mesocarbon microbeads, coke, and synthetic resins such as phenolic resins. Among these carbonaceous material precursors, it is preferable in terms of manufacturing cost to use pitch, which is inexpensive. Pitch can be roughly classified into petroleum-based pitch and coal-based pitch. Examples of petroleum-based pitch include the distillation residue of crude oil, fluid catalytic cracking residue (such as decant oil), bottom oil derived from a thermal cracker, and ethylene tar obtained during naphtha cracking.

[0035] (Other components of the negative electrode active material layer) In this embodiment, the negative electrode active material layer may optionally contain optional components such as a conductive filler, a dispersant, and a binder in addition to the negative electrode active material as necessary.

[0036] The conductive filler preferably consists of a conductive carbonaceous material having higher conductivity than the negative electrode active material. Examples of such conductive fillers include one or more selected from carbon black, carbon nanotubes, graphene, and mixtures thereof. Examples of carbon black include ketjen black and acetylene black. As the conductive filler, it is preferable to use carbon nanotubes in terms of high electron conductivity.

[0037] (Carbon nanotubes) The negative electrode active material layer preferably contains carbon nanotubes. As the carbon nanotubes, single-walled carbon nanotubes and multi-walled carbon nanotubes are preferably used, and single-walled carbon nanotubes are particularly preferably used. The average fiber diameter of the carbon nanotubes is preferably 1 nm or more and less than 20 nm, more preferably 1.5 nm or more and 15 nm or less. If the average fiber diameter is 1 nm or more, the dispersibility of the carbon nanotubes is improved. If the average fiber diameter is less than 20 nm, a non-aqueous alkali metal storage element having higher input / output characteristics can be provided.

[0038] The single-walled carbon nanotubes preferably have a structure in which single-walled carbon nanotubes are bundled (hereinafter referred to as "bundled" single-walled carbon nanotubes). The fiber length of a single single-walled carbon nanotube is about several microns, but it is estimated that the bundled single-walled carbon nanotubes have a fiber length of about several microns to several tens of microns, with a plurality of single-walled carbon nanotubes connected or twisted together. The carbon nanotubes preferably cover the surface of the active material in a network-like manner, and it is also preferable that the carbon nanotubes crosslink the active materials with each other. Here, "network-like" means that a plurality of carbon nanotubes and / or bundled single-walled carbon nanotubes cross each other in various directions on the surface of the active material, forming a structure like the mesh of a net, consisting of a portion covered with carbon nanotubes and a portion where the active material is exposed. The average fiber diameter of the bundled single-walled carbon nanotubes is preferably 5 nm or more and 20 nm or less, more preferably 6 nm or more and 17 nm or less, still more preferably 7 nm or more and 14 nm or less. The bundled single-walled carbon nanotubes tend to form aggregates like cotton balls, but if the average fiber diameter of the bundled single-walled carbon nanotubes is 5 nm or more, the dispersibility is improved, and the formation of aggregates like cotton balls is suppressed. If it is 20 nm or less, the binding property and electron conductivity between the active material particles can be enhanced. The carbon nanotubes can be synthesized by an appropriate method such as chemical vapor deposition, arc discharge method, laser evaporation method, etc.

[0039] When the content of carbon nanotubes in the negative electrode active material layer is based on 100% by mass of the total mass of the negative electrode active material layer, it is preferably 0.003% by mass or more and 0.120% by mass or less. If it is 0.003% by mass or more, the binding property and electron conductivity between the negative electrode active material particles can be enhanced, and the increase in resistance under a high temperature environment of 80°C or higher can be suppressed. If it is 0.120% by mass or less, the carbon nanotubes do not excessively coat the negative electrode active material particles, and the amount of SEI (solid electrolyte interface) generated on the carbon nanotubes in the entire negative electrode active material layer is reduced, so that the ion diffusion resistance can be reduced. At the same time, by reducing the irreversible capacity derived from the carbon nanotubes, the amount of pre-doping of alkali metal ions into the negative electrode can be increased.

[0040] The carbon nanotubes are preferably uniformly dispersed on the surface and between the particles of the negative electrode active material. By uniformly dispersing the carbon nanotubes on the surface and between the particles of the negative electrode active material, the electron conductivity and binding property between the negative electrode active material particles can be enhanced, and the content of the binder can be reduced. Since the binder gradually decomposes under a high temperature environment of 80°C or higher, by reducing the content of the binder, durability under a high temperature environment of 80°C or higher can be imparted.

[0041] The dispersant is not particularly limited. For example, one or more selected from carboxymethyl cellulose, polycarboxylic acid, polycarboxylate, polyvinylpyrrolidone, polyvinyl alcohol, and surfactants are preferably used. In particular, by using two or more of the above dispersants, the dispersibility of the carbon nanotubes and the stability of the coating liquid can be made compatible. The dispersant preferably contains, for example, carboxymethyl cellulose and one or more selected from polyvinylpyrrolidone and polyvinyl alcohol. The content of the dispersion stabilizer is preferably 0.1% by mass or more and 7.0% by mass or less with respect to 100% by mass of the solid content in the negative electrode active material layer. If the amount of the dispersion stabilizer is 7.0% by mass or less, the entry, exit, and diffusion of ions into the negative electrode active material are not inhibited, and high input / output characteristics are exhibited.

[0042] As the binder, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), fluororubber, polyimide, latex, styrene-butadiene copolymer, acrylic copolymer, etc. can be used. The content of the binder in the negative electrode active material layer is preferably 0 to 20% by mass, more preferably in the range of 0.1 to 15% by mass, based on 100% by mass of the negative electrode active material.

[0043] [Negative electrode current collector] As the material constituting the negative electrode current collector according to this embodiment, it is preferably a material with high electronic conductivity that does not cause deterioration due to elution into the electrolyte, reaction with the electrolyte or ions, etc., and may be, for example, a metal foil. There is no particular limitation on such a metal foil, and examples include aluminum foil, copper foil, nickel foil, stainless steel foil, etc. As the negative electrode current collector in the non-aqueous alkali metal storage element according to this embodiment, copper foil is preferable when the non-aqueous electrolyte contains lithium ions, and aluminum foil is preferable when using an electrolyte composed of sodium ions or potassium ions in the non-aqueous electrolyte. The metal foil as the negative electrode current collector may be a normal metal foil without unevenness or through holes, a metal foil with unevenness formed by embossing, chemical etching, electroplating, blasting, etc., or a metal foil with through holes such as expanded metal, punched metal, etched foil. The thickness of the negative electrode current collector is not particularly limited as long as the shape and strength of the negative electrode can be sufficiently maintained, but is, for example, 1 to 100 μm.

[0044] The thickness of the negative electrode active material layer is preferably 10 μm or more and 70 μm or less per side of the current collector, more preferably 15 μm or more and 60 μm or less. If this thickness is 10 μm or more, a good charge-discharge capacity can be exhibited. On the other hand, if this thickness is 70 μm or less, the cell volume can be reduced, so the energy density can be increased. The thickness of the negative electrode active material layer in the case where the negative electrode current collector has holes refers to the average value of the thickness per side of the portion of the negative electrode current collector without holes.

[0045] <Positive electrode> The positive electrode in this embodiment has a positive electrode current collector and a positive electrode active material layer provided on one or both sides thereof. The positive electrode active material layer according to this embodiment contains a positive electrode active material and an alkali metal carbonate.

[0046] As will be described later, in this embodiment, it is preferable to pre-dope the negative electrode with alkali metal ions within the power storage element assembly process. As the pre-doping method, after assembling a power storage element using a positive electrode precursor containing an alkali metal carbonate, a negative electrode, a separator, an exterior body, and a non-aqueous electrolyte, it is preferable to apply a voltage between the positive electrode precursor and the negative electrode. In this case, the alkali metal carbonate may be contained in the positive electrode precursor in any manner. For example, the alkali metal carbonate may be present between the positive electrode current collector and the positive electrode active material layer, may be present on the surface of the positive electrode active material layer, or may be present within the positive electrode active material layer. The alkali metal carbonate is preferably contained in the positive electrode active material layer formed on the positive electrode current collector of the positive electrode precursor. In such a mode, with the pre-doping of alkali metal ions into the negative electrode, pores are formed in the positive electrode active material layer, and the effective area of the positive electrode active material layer increases. In this specification, the positive electrode before the alkali metal doping process is defined as the "positive electrode precursor", and the positive electrode after the alkali metal doping process is defined as the "positive electrode".

[0047] [Positive electrode active material layer] The positive electrode active material layer contains a positive electrode active material and an alkali metal carbonate. In addition to these, the positive electrode active material layer may optionally contain any of the optional components described later as needed.

[0048] (Positive electrode active material) The positive electrode active material preferably contains activated carbon, and in addition to the activated carbon, it may further contain graphene, a conductive polymer, a lithium transition metal oxide, and the like.

[0049] When using activated carbon as the positive electrode active material, there are no particular restrictions on the type of activated carbon and its raw materials. However, in order to achieve both high input / output characteristics and high energy density, it is preferable to optimally control the pores of the activated carbon. Specifically, when the mesopore volume derived from pores with a diameter of 20 Å or more and 500 Å or less calculated by the BJH method is V1 (cc / g), and the micropore volume derived from pores with a diameter of less than 20 Å calculated by the MP method is V2 (cc / g), (1) For high input / output characteristics, activated carbon that satisfies 0.3 < V1 ≤ 0.8, and 0.5 ≤ V2 ≤ 1.0, and has a specific surface area measured by the BET method of 1,500 m 2 / g or more and 3,000 m 2 / g or less (hereinafter also referred to as activated carbon 1) is preferable. Also, (2) To obtain high energy density, activated carbon that satisfies 0.8 < V1 ≤ 2.5, and 0.8 < V2 ≤ 3.0, and has a specific surface area measured by the BET method of 2,300 m 2 / g or more and 4,000 m 2 / g or less (hereinafter also referred to as activated carbon 2) is preferable.

[0050] The BET specific surface area, mesopore volume, micropore volume, and average pore diameter of the active material in this embodiment are values obtained by the following methods respectively. The sample is vacuum-dried at 200 °C for one day and night, and the adsorption and desorption isotherm is measured using nitrogen as the adsorbate. Using the adsorption-side isotherm obtained here, the BET specific surface area is calculated by the BET multi-point method or the BET one-point method, the mesopore volume is calculated by the BJH method, and the micropore volume is calculated by the MP method. The BJH method is a calculation method generally used for the analysis of mesopores and was proposed by Barrett, Joyner, Halenda, etc. (Non-Patent Document 1). The MP method means a method for obtaining the micropore volume, micropore area, and micropore distribution using the "t-plot method" (Non-Patent Document 2), and it is a method devised by R.S. Mikhail, Brunauer, and Bodor (Non-Patent Document 3). The average pore diameter refers to the value obtained by dividing the total pore volume per unit mass of the sample, which is obtained by measuring the equilibrium adsorption amount of nitrogen gas at each relative pressure under liquid nitrogen temperature, by the above BET specific surface area.

[0051] (Activated carbon 1) The mesopore volume V1 of activated carbon 1 is preferably greater than 0.3 cc / g in terms of increasing the input / output characteristics when the positive electrode material is incorporated into the energy storage element. V1 is preferably 0.8 cc / g or less in terms of suppressing the decrease in the bulk density of the positive electrode. V1 is more preferably 0.35 cc / g or more and 0.7 cc / g or less, and even more preferably 0.4 cc / g or more and 0.6 cc / g or less. The micropore volume V2 of activated carbon 1 is preferably 0.5 cc / g or more in order to increase the specific surface area of the activated carbon and the capacity. V2 is preferably 1.0 cc / g or less in terms of suppressing the bulk of the activated carbon, increasing the density as an electrode, and increasing the capacity per unit volume. V2 is more preferably 0.6 cc / g or more and 1.0 cc / g or less, and even more preferably 0.8 cc / g or more and 1.0 cc / g or less. The ratio of the mesopore volume V1 to the micropore volume V2 (V1 / V2) is preferably in the range of 0.3 ≤ V1 / V2 ≤ 0.9. That is, V1 / V2 is preferably 0.3 or more in terms of increasing the ratio of the mesopore volume to the micropore volume to such an extent that the decrease in the output characteristics can be suppressed while maintaining a high capacity. On the other hand, V1 / V2 is preferably 0.9 or less in terms of increasing the ratio of the micropore volume to the mesopore volume to such an extent that the decrease in the capacity can be suppressed while maintaining a high output characteristic. A more preferable range of V1 / V2 is 0.4 ≤ V1 / V2 ≤ 0.7, and an even more preferable range of V1 / V2 is 0.55 ≤ V1 / V2 ≤ 0.7.

[0052] The average pore diameter of activated carbon 1 is preferably 17 Å or more, more preferably 18 Å or more, and most preferably 20 Å or more in terms of maximizing the output of the resulting energy storage element. Also, in terms of maximizing the capacity, the average pore diameter of activated carbon 1 is preferably 25 Å or less. The BET specific surface area of activated carbon 1 is preferably 1,500 m 2 / g or more and 3,000 m 2 / g or less, and more preferably 1,500 m 2 / g or more and 2,500 m 2 / g or less. When the BET specific surface area is 1,500 m 2In the case of / g or more, a good energy density is easily obtained. On the other hand, when the BET specific surface area is 3,000 m 2 / g or less, since it is not necessary to add a large amount of binder to maintain the strength of the electrode, the performance per unit volume of the electrode is improved.

[0053] The activated carbon 1 having the above characteristics can be obtained, for example, using the raw materials and treatment methods described below. In this embodiment, the carbon source used as the raw material of the activated carbon 1 is not particularly limited. For example, plant-based raw materials such as wood, wood powder, coconut shell, by-products during pulp production, bagasse, molasses, etc.; fossil-based raw materials such as peat, lignite, brown coal, bituminous coal, anthracite, petroleum distillation residue components, petroleum pitch, coke, coal tar, etc.; various synthetic resins such as phenol resin, vinyl chloride resin, vinyl acetate resin, melamine resin, urea resin, resorcinol resin, celluloid, epoxy resin, polyurethane resin, polyester resin, polyamide resin, etc.; synthetic rubbers such as polybutylene, polybutadiene, polychloroprene, etc.; other synthetic woods, synthetic pulp, etc., and carbides thereof. Among these raw materials, from the viewpoints of mass production and cost, plant-based raw materials such as coconut shell and wood powder, and carbides thereof are preferable, and coconut shell carbide is particularly preferable.

[0054] As methods for carbonization and activation to use these raw materials as the activated carbon 1, for example, known methods such as a fixed-bed method, a moving-bed method, a fluidized-bed method, a slurry method, a rotary kiln method, etc. can be adopted. As a carbonization method for these raw materials, an inert gas such as nitrogen, carbon dioxide, helium, argon, xenon, neon, carbon monoxide, combustion exhaust gas, or a mixed gas with other gas mainly composed of these inert gases is used, and it is fired at about 400 to 700 °C (preferably 450 to 600 °C) for about 30 minutes to 10 hours. As an activation method for the carbide obtained by the carbonization method described above, a gas activation method of firing using an activation gas such as steam, carbon dioxide, oxygen, etc. is preferably used. Among these, a method of using steam or carbon dioxide as the activation gas is preferable. In this activation method, while supplying the activation gas at a rate of 0.5 to 3.0 kg / h (preferably 0.7 to 2.0 kg / h), it is preferable to raise the temperature of the obtained carbide to 800 to 1,000 °C over 3 to 12 hours (preferably 5 to 11 hours, more preferably 6 to 10 hours) for activation. Further, prior to the activation treatment of the carbide described above, the carbide may be pre-activated once. In this primary activation, usually, a method of firing a carbon material using an activation gas such as steam, carbon dioxide, oxygen, etc. at a temperature below 900 °C for gas activation can be preferably adopted. By appropriately combining the firing temperature and firing time in the carbonization method described above with the activation gas supply amount, heating rate, and maximum activation temperature in the activation method, the activated carbon 1 that can be used in this embodiment can be manufactured.

[0055] The average particle diameter of the activated carbon 1 is preferably 2 to 20 μm. When the average particle diameter is 2 μm or more, the density of the active material layer is high, so the capacity per unit volume of the electrode tends to be high. Although a small average particle diameter may cause a drawback of low durability, such a drawback is less likely to occur if the average particle diameter is 2 μm or more. On the other hand, when the average particle diameter is 20 μm or less, it tends to be more suitable for high-rate charge and discharge. The average particle diameter of the activated carbon 1 is more preferably 2 to 15 μm, and even more preferably 3 to 10 μm.

[0056] (Activated carbon 2) The mesopore volume V1 of the activated carbon 2 is preferably greater than 0.8 cc / g from the viewpoint of increasing the output characteristics when the positive electrode material is incorporated into the energy storage element. V1 is preferably 2.5 cc / g or less from the viewpoint of suppressing a decrease in the capacity of the energy storage element. V1 is more preferably 1.00 cc / g or more and 2.0 cc / g or less, and even more preferably 1.2 cc / g or more and 1.8 cc / g or less. The micropore volume V2 of the activated carbon 2 is preferably greater than 0.8 cc / g in order to increase the specific surface area of the activated carbon and increase the capacity. V2 is preferably 3.0 cc / g or less from the viewpoint of increasing the density of the activated carbon as an electrode and increasing the capacity per unit volume. V2 is more preferably greater than 1.0 cc / g and 2.5 cc / g or less, and even more preferably 1.5 cc / g or more and 2.5 cc / g or less. The activated carbon 2 having the above-described mesopore volume and micropore volume has a higher BET specific surface area than the activated carbon used for conventional electric double layer capacitors or lithium ion capacitors. The specific value of the BET specific surface area of the activated carbon 2 is 2,300 m 2 / g or more and 4,000 m 2 / g or less, preferably 3,000 m 2 / g or more and 4,000 m 2 / g or less, more preferably 3,200 m 2 / g or more and 3,800 m 2 / g or less. When the BET specific surface area is 2,300 m 2 / g or more, a good energy density is easily obtained. When the BET specific surface area is 4,000 m 2 / g or less, it is not necessary to add a large amount of binder to maintain the strength of the electrode, so the performance per unit volume of the electrode is improved.

[0057] The activated carbon 2 having the above characteristics can be obtained, for example, using raw materials and treatment methods as described below. The carbonaceous material used as the raw material for the activated carbon 2 is not particularly limited as long as it is a carbon source usually used as an activated carbon raw material. For example, plant-based raw materials such as wood, wood powder, and coconut shells; fossil-based raw materials such as petroleum pitch and coke; various synthetic resins such as phenolic resin, furan resin, vinyl chloride resin, vinyl acetate resin, melamine resin, urea resin, and resorcinol resin can be mentioned. Among these raw materials, phenolic resin and furan resin are particularly suitable for producing activated carbon with a high specific surface area and are particularly preferred.

[0058] Examples of the method for carbonizing these raw materials or the heating method during the activation treatment include known methods such as a fixed bed method, a moving bed method, a fluidized bed method, a slurry method, and a rotary kiln method. As the atmosphere during heating, an inert gas such as nitrogen, carbon dioxide, helium, or argon, or a gas mixture mainly composed of these inert gases and other gases is used. Generally, the carbonization temperature is about 400 to 700 °C and firing is carried out for about 0.5 to 10 hours. As the activation method of the carbide, there are a gas activation method in which firing is carried out using an activation gas such as water vapor, carbon dioxide, or oxygen, and an alkali metal activation method in which heat treatment is carried out after mixing with an alkali metal compound. However, the alkali metal activation method is preferable for producing activated carbon with a high specific surface area. In this activation method, after mixing so that the mass ratio of the carbide to an alkali metal compound such as KOH or NaOH is 1:1 or more (the amount of the alkali metal compound is the same as or more than the amount of the carbide), heating is carried out in the range of 600 to 900 °C for 0.5 to 5 hours in an inert gas atmosphere, and then the alkali metal compound is washed and removed with acid and water, and further drying may be carried out. In order to increase the micropore volume and not increase the mesopore volume, it is advisable to mix a larger amount of the carbide with KOH during activation. In order to increase both the micropore volume and the mesopore volume, it is advisable to use a larger amount of KOH. Also, in order to mainly increase the mesopore volume, it is preferable to carry out steam activation after the alkali activation treatment. The average particle diameter of Activated Carbon 2 is preferably 2 μm or more and 20 μm or less, more preferably 3 μm or more and 10 μm or less.

[0059] (Usage mode of activated carbon) Activated carbons 1 and 2 may each be a single type of activated carbon or a mixture of two or more types of activated carbons, with each of the above-described characteristic values being shown for the entire mixture. Either one of these activated carbons 1 and 2 may be selected and used, or both may be mixed and used. The positive electrode active material may contain materials other than activated carbons 1 and 2 (for example, activated carbons that do not have the specific V1 and / or V2 described above, or materials other than activated carbons (for example, conductive polymers, etc.)). In an exemplary embodiment, the total content of activated carbons 1 and 2 is preferably 40.0% by mass or more and 70.0% by mass or less, more preferably 45.0% by mass or more and 65.0% by mass or less. If this value is 40.0% by mass or more, the energy density can be increased. If this value is 70.0% by mass or less, the high-temperature durability and high-voltage durability can be improved.

[0060] (Lithium transition metal oxide) It is preferable that the positive electrode active material layer further contains a lithium transition metal compound. By including a lithium transition metal oxide, the non-aqueous alkali metal storage element can be made to have a higher capacity. The lithium transition metal oxide includes a transition metal oxide capable of occluding and releasing lithium. There is no particular limitation on the transition metal oxide used as the positive electrode active material. Examples of the transition metal oxide include oxides containing at least one element selected from the group consisting of cobalt, nickel, manganese, iron, vanadium, and chromium. Specifically, the transition metal oxide has the following formula: Li x CoO2 {wherein x satisfies 0 ≤ x ≤ 1.} Li x NiO2 {wherein x satisfies 0 ≤ x ≤ 1.} Li x Ni y M (1-y) O2 {wherein M is at least one element selected from the group consisting of Co, Mn, Al, Fe, Mg, and Ti, x satisfies 0 ≤ x ≤ 1, and y satisfies 0.05 < y < 0.97.} Li x Ni 1 / 3 Co 1 / 3Mn 1 / 3 O2 {where x satisfies 0 ≦ x ≦ 1.} Li x MnO2 {where x satisfies 0 ≦ x ≦ 1.} α-Li x FeO2 {where x satisfies 0 ≦ x ≦ 1.} Li x VO2 {where x satisfies 0 ≦ x ≦ 1.} Li x CrO2 {where x satisfies 0 ≦ x ≦ 1.} Li x FePO4 {where x satisfies 0 ≦ x ≦ 1.} Li x MnPO4 {where x satisfies 0 ≦ x ≦ 1.} Li z V2(PO4)3 {where z satisfies 0 ≦ z ≦ 3.} Li x Mn2O4 {where x satisfies 0 ≦ x ≦ 1.} Li x M y Mn (2-y) O4 {where M is at least one element selected from the group consisting of Co, Mn, Al, Fe, Mg, and Ti, x satisfies 0 ≦ x ≦ 1, and y satisfies 0.05 < y < 0.97.} Li x Ni a Co b Al (1-a-b) O2 {where x satisfies 0 ≦ x ≦ 1, and a and b satisfy 0.02 < a < 0.97 and 0.02 < b < 0.97.} Li x Ni c Co d Mn (1-c-d) O2 {where x satisfies 0 ≦ x ≦ 1, and c and d satisfy 0.02 < c < 0.97 and 0.02 < d < 0.97.} Compounds represented by the like are exemplified. Among these, from the viewpoints of high capacity, low resistance, cycle characteristics, decomposition of alkali metal carbonate, and suppression of loss of the positive electrode active material during pre-doping, the above formula Li x Ni a Co b Al (1-a-b)O2, Li x Ni c Co d Mn (1-c-d) O2, Li x CoO2, Li x Mn2O4, or Li x FePO4, Li x MnPO4, and Li z Compounds represented by V2(PO4)3 are preferred.

[0061] In the present embodiment, if an alkali metal carbonate different from the positive electrode active material is included in the positive electrode precursor, the alkali metal carbonate can serve as a dopant source of the alkali metal for pre-doping and the negative electrode can be pre-doped. Therefore, even if the transition metal compound does not contain lithium ions in advance (that is, even if x = 0 or z = 0), electrochemical charge and discharge can be performed as a non-aqueous alkali metal storage element. The content of the lithium transition metal oxide in the positive electrode active material layer of the positive electrode precursor is preferably 8.0% by mass or more and 30.0% by mass or less. If the content of the lithium transition metal oxide is 8.0% by mass or more, the non-aqueous alkali metal storage element can be increased in capacity. When the content of the lithium transition metal oxide is 30.0% by mass or less, the non-aqueous alkali metal storage element can be reduced in resistance.

[0062] (Alkali metal carbonate) In the present embodiment, the positive electrode active material layer of the positive electrode precursor may contain an alkali metal carbonate other than the positive electrode active material. The alkali metal carbonate can decompose in the positive electrode precursor to release cations and be reduced at the negative electrode, thereby making it possible to pre-dope the negative electrode. As a result of the positive electrode active material layer of the positive electrode precursor containing the alkali metal carbonate, it is preferable that the positive electrode active material layer of the positive electrode obtained after pre-doping also contains the alkali metal carbonate.

[0063] Examples of such alkali metal carbonates include, specifically, lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, and cesium carbonate. In particular, lithium carbonate, sodium carbonate, or potassium carbonate is more preferably used, and lithium carbonate is particularly preferably used from the viewpoint of high capacity per unit mass.

[0064] The alkali metal carbonate is preferably in the form of fine particles. In the present embodiment, the average particle diameter of the alkali metal carbonate is preferably 0.1 μm or more and 10 μm or less. If the average particle diameter is 0.1 μm or more, the dispersibility in the positive electrode precursor is excellent. If the average particle diameter is 10 μm or less, the decomposition reaction proceeds efficiently because the surface area of the alkali metal carbonate increases. Further, the average particle diameter of the alkali metal carbonate is preferably smaller than the average particle diameter of the activated carbon described above. If the average particle diameter of the alkali metal carbonate is smaller than the average particle diameter of the activated carbon, the electron conduction of the positive electrode active material layer can be enhanced, contributing to a reduction in the resistance of the electrode body or the power storage element. The method for measuring the average particle diameter of the alkali metal carbonate in the positive electrode precursor is not particularly limited, but it can be calculated from the SEM image of the positive electrode cross-section and the SEM-EDX image. For the method of forming the positive electrode cross-section, BIB processing can be used in which an Ar beam is irradiated from the upper part of the positive electrode to produce a smooth cross-section along the edge of the shielding plate installed directly above the sample. Various methods can be used for micronizing the alkali metal carbonate. For example, grinders such as ball mills, bead mills, ring mills, jet mills, and rod mills can be used.

[0065] When the content of the alkali metal carbonate contained in the positive electrode active material layer of the positive electrode precursor is based on 100% by mass of the total mass of the positive electrode active material layer, it is preferably 25.0% by mass or more and 50.0% by mass or less. If this value is 25.0% by mass or more, a sufficient amount of alkali metal ions can be pre-doped into the negative electrode, and the capacity of the non-aqueous alkali metal storage element increases. If this value is 50.0% by mass or less, the electron conduction in the positive electrode precursor can be enhanced, so that the decomposition of the alkali metal carbonate can be efficiently carried out. The quantification of the above alkali metal element and alkaline earth metal element can be performed by ICP-AES, atomic absorption spectrometry, X-ray fluorescence spectrometry, neutron activation analysis, ICP-MS, etc.

[0066] (Other components of the positive electrode active material layer) In the positive electrode active material layer of the positive electrode precursor in the present invention, in addition to the positive electrode active material and the alkali metal carbonate, other components such as a dispersant, a conductive filler, and a binder may be contained as necessary. The dispersant, conductive filler, and binder in the positive electrode active material layer may be appropriately selected from those exemplified above as the dispersant, conductive filler, and binder in the negative electrode active material layer and used. The contents of the dispersant and binder in the positive electrode active material layer may be within the ranges described above as the contents of the dispersant and binder in the negative electrode active material, respectively. The content of the conductive filler in the positive electrode active material layer of the positive electrode precursor is preferably 0 to 20% by mass with respect to 100% by mass of the positive electrode active material. From the viewpoint of high input, it is preferable to blend as much conductive filler as possible. However, if the blending amount exceeds 20% by mass, the content of the positive electrode active material in the positive electrode active material layer decreases, so that the energy density per unit volume of the positive electrode active material layer decreases, which is not preferable.

[0067] (Carbon nanotubes) The positive electrode active material layer preferably contains carbon nanotubes as the conductive filler. The carbon nanotubes contained in the positive electrode active material layer may be the same as those contained in the negative electrode active material layer. Also, the carbon nanotubes can be contained in the positive electrode and / or the negative electrode.

[0068] When the content of the carbon nanotubes in the positive electrode active material layer is based on 100% by mass of the total mass of the positive electrode active material layer, it is preferably 0.010% by mass or more and 0.200% by mass or less. If the content is 0.010% by mass or more, the binding property and electron conductivity between the positive electrode active material particles can be enhanced, the increase in resistance in a high-temperature environment of 80°C or higher can be suppressed, the decomposition of the alkali metal carbonate contained in the positive electrode active material layer can be promoted to suppress the decomposition of the electrolytic solution, and the amount of pre-doping of alkali metal ions into the negative electrode can be increased. If the content is 0.200% by mass or less, the positive electrode active material particles will not be overly coated with carbon nanotubes, and since the abundance of SEI (solid electrolyte interface) formed on the carbon nanotubes in the entire positive electrode active material layer is reduced, the ion diffusion resistance can be reduced.

[0069] Preferably, the carbon nanotubes are uniformly dispersed on the surface and between the particles of the positive electrode active material. By uniformly dispersing the carbon nanotubes on the surface and between the particles of the positive electrode active material, the electron conductivity and binding property between the positive electrode active material particles can be enhanced, and the content of the binder can be reduced. Since the binder gradually decomposes in a high-temperature environment of 80°C or higher, durability in a high-temperature environment of 80°C or higher can be imparted by reducing the content of the binder.

[0070] By uniformly dispersing the carbon nanotubes on the surface and between the particles of the positive electrode active material, the electron conductivity and binding property between the positive electrode active material particles can be enhanced, and the content of the binder can be reduced. Since the binder gradually decomposes in a high-temperature environment of 80°C or higher or in a high-voltage environment of 4.1 V or higher, high-temperature durability of 80°C or higher and high-voltage durability of 4.1 V or higher can be imparted by reducing the content of the binder.

[0071] [Positive current collector] As the material constituting the positive electrode current collector according to this embodiment, there is no particular limitation as long as it has high electronic conductivity and does not deteriorate due to elution into the electrolytic solution or reaction with the electrolyte or ions, etc., but a metal foil is preferred. As the positive electrode current collector in the non-aqueous alkali metal storage element according to this embodiment, an aluminum foil is more preferred. The metal foil may be a normal metal foil without unevenness or through holes, or a metal foil having unevenness subjected to embossing, chemical etching, electrodeposition method, blasting, etc., or a metal foil having through holes such as expanded metal, punching metal, etched foil, etc. From the viewpoint of the alkali metal doping step described later, a non-porous aluminum foil is more preferred, and it is particularly preferred that the surface of the aluminum foil is roughened. The thickness of the positive electrode current collector is not particularly limited as long as the shape and strength of the positive electrode can be sufficiently maintained. For example, 1 to 100 μm is preferred. It is preferable to provide an anchor layer containing a conductive material such as graphite, flaky graphite, carbon nanotubes, graphene, ketjen black, acetylene black, vapor-grown carbon fibers, etc. on the surface of the metal foil. By providing the anchor layer, the electrical conduction between the positive electrode current collector and the positive electrode active material layer can be improved and the resistance can be reduced. The thickness of the anchor layer is preferably 0.1 μm or more and 5 μm or less per one side of the positive electrode current collector.

[0072] The positive electrode current collector according to this embodiment has a protective layer and a non-protective layer. By providing a protective layer on the positive electrode current collector, corrosion of the current collector in a high-temperature and high-voltage environment can be suppressed. In addition, by providing a non-protective layer on the positive electrode current collector, the welding strength between the positive electrode current collector and the positive electrode terminal can be increased, and the electron transfer resistance of the welded portion can be reduced. The protective layer on the positive electrode current collector may be present on one side of the positive electrode current collector or on both sides.

[0073] The material of the positive electrode protective layer is not limited, and examples thereof include a protective tape, a carbon layer, and an inorganic fine particle layer. The protective tape is preferably insulating, and as the base material, for example, at least one material selected from the group consisting of polyether ketone, polyphenylene sulfide, polyethylene terephthalate, polyethylene naphthalate, polyamide, polyimide, aramid, acetate cloth, and polytetrafluoroethylene tape is preferably used. The carbon layer is not particularly limited, and for example, at least one carbon material selected from the group consisting of carbon black, graphite, graphene, and carbon nanotubes is preferably used. Further, as the carbon layer, the above-described anchor layer can be provided wider than the active material layer and used as a protective layer. The inorganic fine particle layer is not particularly limited, and for example, at least one material selected from the group consisting of aluminum oxide, silicon oxide, and zirconia is preferably used as the inorganic fine particles.

[0074] The non-protective layer means a portion of the positive electrode that does not have a protective layer, and the material thereof is not limited. For example, a portion where the positive electrode current collector is exposed in the positive electrode may be referred to as a non-protective layer.

[0075] The thickness of the positive electrode active material layer according to this embodiment is preferably 10 μm or more and 200 μm or less per one side of the positive electrode current collector. The thickness of the positive electrode active material layer is more preferably 20 μm or more and 150 μm or less per one side, and even more preferably 30 μm or more and 100 μm or less. If this thickness is 10 μm or more, a sufficient charge and discharge capacity can be exhibited. On the other hand, if this thickness is 200 μm or less, the ion diffusion resistance in the electrode can be maintained low. Therefore, sufficient output characteristics can be obtained, the cell volume can be reduced, and thus the energy density can be increased. Note that the thickness of the positive electrode active material layer in the case where the positive electrode current collector has a through hole or unevenness refers to the average value of the thickness per one side of the portion of the positive electrode current collector that does not have a through hole or unevenness.

[0076] <Separator> The positive electrode precursor and the negative electrode are laminated via a separator, or laminated and wound, to form an electrode laminate or an electrode wound body having the positive electrode precursor, the negative electrode, and the separator. As the separator, a microporous membrane made of polyethylene or a microporous membrane made of polypropylene used in a lithium ion secondary battery, or a nonwoven paper made of cellulose used in an electric double layer capacitor can be used. A film made of organic or inorganic fine particles may be laminated on one or both surfaces of these separators. Also, organic or inorganic fine particles may be contained inside the separator. The thickness of the separator is preferably 5 μm or more and 35 μm or less. A thickness of 5 μm or more is preferable because self-discharge due to internal micro-short circuits tends to be reduced. On the other hand, a thickness of 35 μm or less is preferable because the output characteristics of the power storage element tend to be improved. Also, the thickness of the film made of organic or inorganic fine particles is preferably 1 μm or more and 10 μm or less. Making the thickness of this film 1 μm or more is preferable because self-discharge due to internal micro-short circuits tends to be reduced. On the other hand, making the thickness of this film 10 μm or less is preferable because the output characteristics of the power storage element tend to be improved.

[0077] 〈Outer package〉 As the outer package, a metal can, a laminate film, etc. can be used. As the metal can, an aluminum one is preferable. The metal can may be in a form such as square, round, cylindrical, etc. As the laminate film, a film in which a metal foil and a resin film are laminated is preferable, and an example is a three-layer structure composed of an outer layer resin film / metal foil / inner layer resin film. The outer layer resin film is for preventing the metal foil from being damaged by contact, etc., and resins such as nylon or polyester can be preferably used. The metal foil is for preventing the permeation of moisture and gas, and foils such as copper, aluminum, stainless steel, etc. can be preferably used. Also, the inner layer resin film is for protecting the metal foil from the electrolytic solution stored inside and for melt-sealing during heat-sealing of the outer package, and polyolefin, acid-modified polyolefin, etc. can be preferably used.

[0078] <Electrolyte Solution> The electrolyte solution in this embodiment is a non-aqueous electrolyte solution. That is, this electrolyte solution contains a non-aqueous solvent. The non-aqueous electrolyte solution contains an alkali metal salt of 0.5 mol / L or more based on the total amount of the non-aqueous electrolyte solution. That is, the non-aqueous electrolyte solution contains an alkali metal salt as an electrolyte. Examples of the non-aqueous solvent contained in the non-aqueous electrolyte solution include cyclic carbonates typified by ethylene carbonate, propylene carbonate, etc., and chain carbonates typified by dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc.

[0079] As the electrolyte salt containing alkali metal ions dissolved in the non-aqueous solvent as described above, for example, when M is Li, Na, K, Rb or Cs, MFSI, MBF4, MPF6, MClO4, LiB(C2O4)2, LiBF2(C2O4), etc. can be used.

[0080] The concentration of the electrolyte salt in the electrolyte solution is preferably in the range of 0.5 to 2.0 mol / L. At an electrolyte salt concentration of 0.5 mol / L or more, anions are sufficiently present and the capacity of the non-aqueous alkali metal storage element is maintained. On the other hand, at an electrolyte salt concentration of 2.0 mol / L or less, the salt is sufficiently dissolved in the electrolyte solution, and appropriate viscosity and conductivity of the electrolyte solution are maintained. The concentration of the electrolyte salt of MPF6 contained in the non-aqueous electrolyte solution in this embodiment is preferably in the range of 0.00 mol / L or more and 0.05 mol / L. If the concentration is 0.05 mol / L or less, the decomposition of hexafluorophosphate ions in a high-temperature environment can be suppressed, and the increase in resistance during high-temperature and high-voltage cycles can be suppressed. From the same viewpoint, in the non-aqueous alkali metal storage element according to this embodiment, the concentration of hexafluorophosphate ions (PF6 - ) contained in the non-aqueous electrolyte solution is preferably 0.00 mol / L or more and 0.05 mol / L or less.

[0081] The water content contained in the non-aqueous electrolyte is preferably 0 ppm or more and 500 ppm or less. If the water content is 0 ppm or more, the alkali metal carbonate in the positive electrode precursor can be slightly dissolved, so that pre-doping can be carried out under mild conditions, resulting in increased capacity and reduced resistance. If the water content is 500 ppm or less, the decomposition of the electrolyte is suppressed, improving the high-temperature storage characteristics. The water content in the electrolyte can be measured by the above-described Karl Fischer method.

[0082] 《Method for manufacturing non-aqueous alkali metal storage element》 [Manufacture of negative electrode] The negative electrode has a negative electrode active material layer on one or both surfaces of a negative electrode current collector. In a typical embodiment, the negative electrode active material layer is fixed to the negative electrode current collector. The negative electrode can be manufactured by the manufacturing techniques of electrodes in known lithium-ion secondary batteries, electric double layer capacitors, etc. For example, various materials containing a negative electrode active material are dispersed or dissolved in water or an organic solvent to prepare a slurry-like coating liquid, and this coating liquid is coated on one or both surfaces of a negative electrode current collector to form a coating film, which is dried to obtain a negative electrode. Further, the obtained negative electrode may be pressed to adjust the film thickness or bulk density of the negative electrode active material layer.

[0083] The method for preparing the coating liquid is not particularly limited, but preferably, it can be carried out using a disperser such as a homodisper, multi-axis disperser, planetary mixer, thin-film swirling high-speed mixer, etc. In order to obtain a coating liquid in a good dispersion state, it is preferable to disperse the coating liquid at a peripheral speed of 1 m / s or more and 50 m / s or less. If the peripheral speed is 1 m / s or more, it is preferable because various materials are well dissolved or dispersed. If the peripheral speed is 50 m / s or less, it is preferable because re-aggregation is suppressed without the various materials being destroyed by the heat or shear force due to dispersion.

[0084] The degree of dispersion of the coating liquid preferably has a particle size measured by a particle gauge of 0.1 μm or more and 100 μm or less. As the upper limit of the degree of dispersion, as the particle size measured by the particle gauge, more preferably it is 80 μm or less, and still more preferably 50 μm or less. If the particle size is within this range, nozzle clogging during coating, streak generation in the coating film, etc. can be suppressed without crushing the material during the preparation of the coating liquid, and stable coating can be achieved.

[0085] The viscosity (ηb) of the coating liquid is preferably 100 mPa·s or more and 10,000 mPa·s or less, more preferably 300 mPa·s or more and 5,000 mPa·s or less, and still more preferably 500 mPa·s or more and 3,000 mPa·s or less. If the viscosity (ηb) is 100 mPa·s or more, dripping of the liquid during film formation is suppressed, and the coating film width and thickness can be well controlled. Also, if the viscosity is 10,000 mPa·s or less, the pressure loss in the flow path of the coating liquid when using a coating machine is small, stable coating can be performed, and control of the coating film thickness becomes easy.

[0086] The TI value (thixotropy index value) of the coating liquid is preferably 1.1 or more, more preferably 1.2 or more, and still more preferably 1.5 or more. If the TI value is 1.1 or more, the coating film width and thickness can be well controlled.

[0087] Although there are no particular restrictions on the formation of the coating film of the negative electrode active material layer, it is preferably possible to use a coating machine such as a die coater, comma coater, knife coater, gravure coater, etc. The coating film may be formed by single-layer coating or by multi-layer coating. In the case of multi-layer coating, the coating liquid composition may be adjusted so that the content of the components in each layer of the coating film is different. When coating the coating film on the negative electrode current collector, multi-strip coating, intermittent coating, or multi-strip intermittent coating may be performed. When forming the negative electrode active material layer on both sides of the negative electrode current collector, sequential coating may be performed in which the coating is applied and dried on one side of the negative electrode current collector and then the coating is applied and dried on the other side, or double-sided simultaneous coating may be performed in which the coating liquid is applied and dried on both sides of the negative electrode current collector at the same time. Also, in this case, the difference in thickness between the negative electrode active material layers on the front and back surfaces of the negative electrode current collector is preferably 10% or less of the average thickness of the two. The closer the mass ratio and film thickness ratio of the negative electrode active material layers on the front and back surfaces are to 1.0, the less the charge and discharge load will concentrate on one side, and thus the high-load charge and discharge cycle characteristics will be improved.

[0088] After forming the coating film of the negative electrode active material layer on the negative electrode current collector, the coating film is dried. The drying of the coating film of the negative electrode precursor is preferably performed by an appropriate drying method such as hot air drying or infrared (IR) drying, preferably by far-infrared rays, near-infrared rays, or hot air. The coating film may be dried at a single temperature or may be dried with the temperature changed stepwise. The coating film may be dried by combining a plurality of drying methods. The drying temperature is preferably 25°C or higher and 200°C or lower, more preferably 40°C or higher and 180°C or lower, and even more preferably 50°C or higher and 160°C or lower. If the drying temperature is 25°C or higher, the solvent in the coating film can be sufficiently volatilized. On the other hand, if it is 200°C or lower, cracking of the coating film due to rapid volatilization of the solvent, uneven distribution of the binder due to migration, or oxidation of the negative electrode current collector or the negative electrode active material layer can be suppressed.

[0089] The water content in the negative electrode active material layer after drying is preferably 0.1% by mass or more and 10% by mass or less, based on 100% by mass of the total mass of the negative electrode active material layer. If the water content is 0.1% by mass or more, deterioration of the binder due to excessive drying can be suppressed and the resistance can be reduced. If the water content is 10% by mass or less, deactivation of alkali metal ions can be suppressed and the capacity can be increased. When N-methyl-2-pyrrolidone (NMP) is used for adjusting the coating liquid, the content of NMP in the negative electrode active material layer after drying is preferably 0.1% by mass or more and 10% by mass or less, based on 100% of the total mass of the negative electrode active material layer. The water content in the negative electrode active material layer can be measured, for example, by the Karl Fischer titration method (JIS 0068(2001) "Method for Measuring Water Content of Chemical Products"). The amount of NMP contained in the negative electrode active material layer can be extracted by immersing the negative electrode active material layer in ethanol with a mass 50 to 100 times that of the negative electrode active material layer for 24 hours at 25°C, and then GC / MS is measured and quantified based on a calibration curve prepared in advance.

[0090] For pressing the negative electrode active material layer, an appropriate pressing machine such as a hydraulic press, a vacuum press, or a roll press can preferably be used. The film thickness, bulk density, and electrode strength of the negative electrode active material layer can be adjusted by the pressing pressure, the gap between the pressing rolls, and the surface temperature of the pressing part, which will be described later. The pressing pressure is preferably 0.5 kN / cm or more and 20 kN / cm or less, more preferably 1 kN / cm or more and 10 kN / cm or less, and even more preferably 2 kN / cm or more and 7 kN / cm or less. If the pressing pressure is 0.5 kN / cm or more, the electrode strength can be made sufficiently high. On the other hand, if the pressing pressure is 20 kN / cm or less, bending and wrinkles will not occur in the negative electrode, and the negative electrode active material layer can be adjusted to a desired film thickness or bulk density. When a roll press is used for pressing, an appropriate value can be set as the gap between the pressing rolls so that the negative electrode active material layer has a desired thickness and bulk density. The pressing speed can be set to an appropriate speed at which bending and wrinkles do not occur in the negative electrode.

[0091] The surface temperature of the pressing part may be room temperature, or it may be heated if necessary. When heating, the lower limit of the surface temperature of the pressing part is preferably not less than the melting point of the binder used minus 60°C, more preferably not less than the melting point of the binder minus 45°C, and even more preferably not less than the melting point of the binder minus 30°C. On the other hand, when heating, the upper limit of the surface temperature of the pressing part is preferably not more than the melting point of the binder used plus 50°C, more preferably not more than the melting point of the binder plus 30°C, and even more preferably not more than the melting point of the binder plus 20°C. For example, when using polyvinylidene fluoride (melting point 150°C) as the binder, it is preferable to heat the pressing part to 90°C or higher and 200°C or lower, more preferably 105°C or higher and 180°C or lower, and even more preferably 120°C or higher and 170°C or lower. Also, when using a styrene-butadiene copolymer (melting point 100°C) as the binder, it is preferable to heat the pressing part to 40°C or higher and 150°C or lower, more preferably 55°C or higher and 130°C or lower, and even more preferably 70°C or higher and 120°C or lower. The melting point of the binder can be determined at the endothermic peak position of DSC (Differential Scanning Calorimetry). For example, when using a differential scanning calorimeter "DSC7" manufactured by PerkinElmer, setting 10 mg of the sample resin in the measurement cell and heating it from 30°C to 250°C at a heating rate of 10°C / min in a nitrogen gas atmosphere, the endothermic peak temperature in the heating process becomes the melting point.

[0092] Multiple pressings may be performed while changing the conditions of the pressing pressure, gap, speed, and the surface temperature of the pressing part. When the negative electrode active material layer is coated in multiple layers, it is preferable to slit it before pressing. If the negative electrode active material layer coated in multiple layers is pressed without slitting, excessive stress may be applied to the negative electrode current collector part where the negative electrode active material layer is not coated, and wrinkles may occur. After pressing, the negative electrode active material layer may be slit again.

[0093] [Manufacture of Cathode Precursor] In this embodiment, the positive electrode precursor serving as the positive electrode of the non-aqueous alkali metal storage element can be manufactured by the manufacturing techniques of electrodes in known lithium ion secondary batteries, electric double layer capacitors, etc. For example, a positive electrode active material, an alkali metal carbonate, and other optional components used as necessary are dispersed or dissolved in water or an organic solvent to prepare a slurry-like coating liquid, and this coating liquid is applied to one side or both sides of a positive electrode current collector to form a coating film, and by drying this, a positive electrode precursor can be obtained. Further, the obtained positive electrode precursor may be pressed to adjust the film thickness or bulk density of the positive electrode active material layer. Preparation of the coating liquid for forming the positive electrode active material layer, application of the coating liquid onto the positive electrode current collector, drying of the coating film, and pressing can each be carried out according to the methods described above for the manufacture of the negative electrode.

[0094] [Assembly process] In the assembly process of one embodiment, for example, a positive electrode precursor cut into a single-sheet shape and a negative electrode are laminated via a separator, and a positive electrode terminal and a negative electrode terminal are connected to the laminated body to produce an electrode laminate. In another embodiment, the positive electrode precursor and the negative electrode may be laminated and wound via a separator, and a positive electrode terminal and a negative electrode terminal may be connected to the wound body to produce an electrode wound body. The shape of the electrode wound body may be cylindrical or flat. The method of connecting the positive electrode terminal and the negative electrode terminal is not particularly limited, and methods such as resistance welding and ultrasonic welding can be used. It is preferable to dry the electrode body (electrode laminate or electrode wound body) to which the terminals are connected to remove the remaining solvent. The drying method is not limited, and drying can be performed by vacuum drying or the like. The remaining solvent is preferably 1.5% by mass or less per total mass of the positive electrode active material layer or the negative electrode active material layer. If the remaining solvent is more than 1.5% by mass, the solvent remains in the system, which is not preferable because it deteriorates the self-discharge characteristics. The dried electrode body is preferably stored in an exterior body typified by a metal can or a laminate film in a dry environment with a dew point of -40°C or lower, and only one opening for injecting a non-aqueous electrolyte is left and sealed. If the dew point is higher than -40°C, moisture adheres to the electrode body, water remains in the system, and the self-discharge characteristics deteriorate, which is not preferable. The sealing method of the exterior body is not particularly limited, and methods such as heat sealing and impulse sealing can be used.

[0095] The non-aqueous alkali metal storage element according to this embodiment is characterized in that, on the projection plane in the stacking direction of the electrode body, the protective layer of the positive electrode current collector and the negative electrode end portion described above overlap. In the charge and discharge of the non-aqueous alkali metal storage element, when there is a positive electrode current collector that does not face the negative electrode active material layer or a negative electrode current collector that does not face the positive electrode active material layer, the potential fluctuation at such a current collector portion becomes abrupt. In particular, in a non-aqueous electrolyte, hexafluorophosphate ions (PF6 -) When the abundance is 0.05 mol / L or less, a stable passive film is not formed on the positive electrode current collector, and in the high-temperature and high-voltage cycles described later, the corrosion of the current collector progresses and the resistance increases. Therefore, by providing the positive electrode protective layer on the positive electrode current collector facing the negative electrode active material layer, the corrosion of the positive electrode current collector can be suppressed.

[0096] FIG. 1 is a schematic projected view in the stacking direction of an electrode body according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of an electrode body according to an embodiment of the present invention. By referring to FIGS. 1 and 2, in the electrode body (E), the negative electrode (1), the negative electrode end (e), the negative electrode current collector (2), the negative electrode active material layer (3), the separator (4), the positive electrode (5), the positive electrode current collector (6), the positive electrode active material layer (7), the protective layer (8), the non-protective layer (9), etc. can be positioned.

[0097] [Liquid injection, impregnation, and sealing process] After the assembly process, a non-aqueous electrolyte is injected into the electrode body housed in the exterior body. After the liquid injection, it is further desirable to perform impregnation to sufficiently immerse the positive electrode, negative electrode, and separator in the non-aqueous electrolyte. When at least a part of the positive electrode, negative electrode, and separator is not immersed in the electrolyte, in the alkali metal doping process described later, the alkali metal doping proceeds unevenly, so that the resistance of the obtained non-aqueous alkali metal storage element increases or the durability decreases. The impregnation method is not particularly limited. For example, after the liquid injection, the electrode body is placed in a decompression chamber with the exterior body open, the inside of the chamber is decompressed using a vacuum pump, and the method of returning to atmospheric pressure again can be used. After impregnation, it can be sealed by sealing the electrode body with the exterior body open while decompressing.

[0098] [Alkali metal doping process] In the alkali metal doping process, it is preferable to apply a voltage between the positive electrode precursor and the negative electrode to decompose the alkali metal carbonate preferably contained in the positive electrode precursor to release alkali metal ions, and reduce the alkali metal ions at the negative electrode, thereby pre-doping the negative electrode active material layer with alkali metal ions. In the alkali metal doping process, gases such as CO2 are generated due to the oxidative decomposition of the alkali metal carbonate in the positive electrode precursor. Therefore, when applying the voltage, it is preferable to take measures to release the generated gas to the outside of the exterior body. Examples of such measures include a method of applying a voltage with a part of the exterior body opened; a method of applying a voltage with appropriate gas release means such as a gas vent valve or a gas permeable film installed in advance in a part of the exterior body; and the like. Also, in the alkali metal doping process, it is preferable to sandwich both sides of the central part of the electrode body sealed in the exterior body with a cushioning material and apply pressure, and it is more preferable to sandwich both sides of the central part of the electrode body with a cushioning material from the outside of the exterior body and apply pressure. The pressure during pressurization is preferably 10 kPa or more and 1000 kPa or less. If the pressure during pressurization is 10 kPa or more, the gas generated in the doping process is discharged from the inside of the electrode body, and the decomposition of the alkali metal carbonate is promoted. If the pressure during pressurization is 1000 kPa or less, the non-aqueous electrolyte is sufficiently retained in the electrode body, so the decomposition of the alkali metal carbonate is promoted. Examples of the cushioning material include silicon sponge, silicon rubber, chloroprene rubber, butyl rubber, urethane rubber, styrene-butadiene rubber, acrylonitrile rubber, and the like.

[0099] [Aging Process] After the alkali metal doping process, it is preferable to age the electrode body. In the aging process, the solvent in the electrolyte decomposes at the negative electrode, and a solid polymer film permeable to alkali metal ions is formed on the surface of the negative electrode. The method of aging is not particularly limited, and for example, a method of reacting the solvent in the electrolyte in a high-temperature environment can be used.

[0100] [Gas Venting Process] After the aging process, it is preferable to further degas to surely remove the gas remaining in the electrolytic solution, the positive electrode, and the negative electrode. When gas remains in at least a part of the electrolytic solution, the positive electrode, and the negative electrode, ion conduction is inhibited, so that the resistance of the obtained non-aqueous alkali metal storage element increases. The degassing method is not particularly limited. For example, a method can be used in which the electrode body is placed in a decompression chamber with the exterior body open and the inside of the chamber is decompressed using a vacuum pump. After degassing, the exterior body can be sealed by sealing the exterior body to produce a non-aqueous alkali metal storage element.

[0101] [High-temperature and high-voltage cycle characteristics] In a high-temperature environment of 85°C or higher and a high-voltage environment of 4.0 V or higher, the decomposition reaction of the electrolytic solution is likely to be promoted. At the negative electrode, reduction reaction of the electrolytic solution solvent proceeds on the negative electrode where alkali metal ions are doped and the potential becomes low. In particular, at the electrode end, since there is a large amount of surplus electrolytic solution around it, this side reaction is likely to proceed. Further, in a high-temperature environment, deactivation of the alkali metal ions doped in the negative electrode active material is promoted, so that the potential is likely to increase, and as a result, the capacity is likely to decrease. That is, by suppressing the side reaction at the negative electrode end and suppressing the deactivation of the alkali metal ions doped in the negative electrode, it is possible to suppress the increase in resistance and improve the capacity retention rate in the high-temperature and high-voltage cycle.

[0102] The side reaction at the negative electrode end correlates with the concentration of alkali metal ions present at the negative electrode end. That is, the lower the amount of alkali metal ions per unit area on the outer peripheral part of the negative electrode, the lower the reactivity. On the other hand, by increasing the amount of alkali metal ions in the central part of the negative electrode, even if some of the alkali metal ions doped into the negative electrode are deactivated, the increase in potential can be suppressed. That is, when the alkali metal ion concentration per unit area of the outer peripheral part of the negative electrode is A (mAh / g) and the alkali metal ion concentration per unit area of the central part is B (mAh / g), when 1.02 ≤ B / A ≤ 1.45, it is possible to suppress the increase in resistance and improve the capacity retention rate in high-temperature and high-voltage cycles. If B / A is 1.02 or more, the increase in resistance in high-temperature and high-voltage cycles can be suppressed by suppressing the side reaction at the negative electrode end. If B / A is 1.45 or less, the excessive potential increase at the positive electrode end facing the negative electrode end can be suppressed, and the increase in resistance can be suppressed by suppressing the corrosion of the positive electrode current collector. From this perspective, 1.03 ≤ B / A ≤ 1.44 is preferable. Note that Fig. 3 is an image diagram showing the outer peripheral part and the central part of the negative electrode, and displays a schematic top view (a) of the negative electrode and a schematic diagram (b) for explaining the outer peripheral part, the central part, and the end part of the negative electrode. By referring to Fig. 3, the outer peripheral part (о) and the central part (c) of the negative electrode to be measured (1) can be defined. In the negative electrode (1), a negative electrode active material layer (3) is disposed on a negative electrode current collector (2). The central part (c) is a region surrounded by a dotted line located at 5% of the length from the electrode end (e) indicated by the thick line toward the center. The outer peripheral part (о) is a region surrounded by the dotted line and the thick line.

[0103] The method of making B / A be 1.02 or more and 1.45 or less is not particularly limited. For example, a method of increasing the concentration of alkali metal carbonate in the central part of the positive electrode precursor facing the negative electrode, a method of locally heating the central part of the electrode body during alkali metal doping to promote the alkali metal doping reaction in the central part, a method of locally pressurizing the central part of the electrode body during alkali metal doping to promote the alkali metal doping reaction in the central part, a method of assembling the electrode body using a negative electrode in which the central part has been previously doped with an alkali metal, etc. can be mentioned.

[0104] [Calculation methods for A and B] The alkali metal ion concentration A per unit area of the outer peripheral part and the alkali metal ion concentration B per unit area of the central part can be determined by the following method.

[0105] First, after adjusting the voltage of the non-aqueous alkali metal storage element to 3.8 V in a 25°C environment, it is disassembled in an argon atmosphere with a dew point of -60°C or lower, and the negative electrode is taken out. For the obtained negative electrode, it is washed twice with dimethyl carbonate, air-dried, and then the electrode is cut out in a region including a distance within 5% from the electrode end to obtain a sample of the outer peripheral part. Also, with the position at the longest distance from the electrode end as the center point, the electrode is cut out in a region including this center point to obtain a sample of the central part. Although there is no particular specification regarding the area of the electrode to be cut out, when taking the electrode area of the negative electrode including the active material layer as 100%, it is preferable to cut out the electrode so that the area is 5% or more and 20% or less. Using the obtained sample as the working electrode, a separator, and metallic lithium as the counter electrode and reference electrode, the above-mentioned non-aqueous electrolyte is injected to fabricate a negative electrode half-cell. For the working electrode sample, when the active material layer exists on both sides of the current collector, the active material layer on one side is peeled off using a spatula or a brush. Regarding the non-aqueous electrolyte to be used, an electrolyte salt containing the same cation as the alkali metal ion species doped in the negative electrode is used, and a mixed solvent of a chain carbonate and a cyclic carbonate (for example, a mixed solvent with a volume ratio of ethylene carbonate to ethyl methyl carbonate of 1:2) is preferably used. Regarding the obtained negative electrode half-cell, at a current value of 0.1 mA / cm 2 in a 25°C environment, constant current charging is performed until the potential of the working electrode reaches 2.5 V. Regarding the charging capacity at this time, for example, while referring to FIG. 3, taking the evaluation result of the sample of the outer peripheral part as A1 (mAh) and the evaluation result of the sample of the central part as B1 (mAh), A and B can be calculated by dividing A1 and B1 by the weight of the active material layer of the working electrode sample.

[0106] [In the case of a negative electrode having an active material layer on both the outermost layers] When the outermost layer of the electrode laminate or the wound electrode body is the negative electrode and the negative electrode active material layer is provided on both surfaces of the negative electrode current collector of the negative electrode, when the alkali metal ion concentration per unit area at the center of the negative electrode active material layer that is not opposed to the positive electrode is E (mAh / g), it is preferable that B > E. By setting B > E, side reactions on the outermost negative electrode can be suppressed. The calculation of E can be obtained in the same manner as the above-described alkali metal ion concentration B.

[0107] 《Applications of Non-aqueous Alkali Metal Storage Elements》 A power storage module can be produced by connecting a plurality of non-aqueous alkali metal storage elements according to the present embodiment in series or in parallel. The non-aqueous alkali metal storage element and the power storage module of the present embodiment can achieve both high input / output characteristics and safety at high temperatures. Therefore, it can be used in a power regeneration assist system, a power load leveling system, an uninterruptible power supply system, a non-contact power supply system, an energy harvesting system, a power storage system, a solar power generation power storage system, an electric power steering system, an emergency power supply system, an in-wheel motor system, an idling stop system, a rapid charging system, a smart grid system, etc. The power storage system is preferably used for natural power generation such as solar power generation or wind power generation, the power load leveling system is preferably used for a microgrid or the like, and the uninterruptible power supply system is preferably used for factory production facilities or the like. In the non-contact power supply system, the non-aqueous alkali metal storage element is for equalization of voltage fluctuations such as microwave power transmission or electric field resonance and energy storage; in the energy harvesting system, the non-aqueous alkali metal storage element is preferably used for using the power generated by vibration power generation or the like.

[0108] In a power storage system, as a cell stack, a plurality of non-aqueous alkali metal power storage elements are connected in series or in parallel, or a non-aqueous alkali metal power storage element and a lead battery, a nickel-metal hydride battery, a lithium-ion secondary battery, or a fuel cell are connected in series or in parallel. Further, since the non-aqueous alkali metal power storage element according to the present embodiment can achieve both high input / output characteristics and safety at high temperatures, it can be mounted on vehicles such as electric vehicles, plug-in hybrid vehicles, hybrid vehicles, and electric motorcycles, for example. The power regeneration assist system, the electric power steering system, the emergency power supply system, the in-wheel motor system, the idling stop system, or a combination thereof described above is preferably mounted on a vehicle.

Example

[0109] Hereinafter, embodiments of the present invention will be specifically described by showing examples and comparative examples. However, the present invention is not limited by the following examples and comparative examples. In the following description, abbreviations CMC1, CMC2, and CMC3 are used, but CMC1 to CMC3 are for the calculation of the blending ratio and are the same carboxymethyl cellulose.

[0110] <<Manufacturing Examples of Negative Electrode, Positive Electrode Precursor, and Electrolyte>> [Preparation of Carbon Nanotube Dispersion Liquid] 0.400 mass% of commercially available single-walled carbon nanotubes (CNT), 0.600 mass% of carboxymethyl cellulose (CMC1) as a dispersant, and 99.000 mass% of distilled water were mixed and dispersed under the condition of a peripheral speed of 17 m / s using a thin-film swirling type high-speed mixer Filmix manufactured by PRIMIX Corporation to prepare a carbon nanotube dispersion liquid.

[0111] [Manufacture of Negative Electrode 1] 94.800 mass% of artificial graphite with an average particle diameter of 4.5 μm, 3.000 mass% of carbon black, 2.000 mass% of carboxymethyl cellulose (CMC2) as a dispersant, and distilled water were mixed to obtain a mixture with a solid content mass ratio of 28.0 mass%. The obtained mixture was dispersed for 10 minutes at a rotational speed of 2,000 rpm using a planetary mixer "Awa Torikintaro (registered trademark)" manufactured by Shinki Co., Ltd. to obtain a mixture. To the above-prepared mixture, a carbon nanotube dispersion was mixed so that the carbon nanotubes (CNT) were 0.080 mass% and CMC1 was 0.120 mass%, and dispersed for 10 minutes at a rotational speed of 2,000 rpm to prepare a negative electrode coating liquid 1. The viscosity (ηb) and TI value of the obtained negative electrode coating liquid 1 were measured using an E-type viscometer TVE-35H manufactured by Toki Sangyo Co., Ltd. As a result, the viscosity (ηb) was 1,560 mPa·s and the TI value was 3.7. Negative electrode coating liquid 1 was coated on one side of an electrolytic copper foil with a thickness of 10 μm using a doctor blade and dried for 10 minutes on a hot plate heated to 50°C. Then, using a roll press machine, a negative electrode 1 was prepared by pressing under the conditions of a pressure of 5 kN / cm and a surface temperature of 25°C in the pressing part. The negative electrode 1 was cut into a size of 3 cm × 3 cm, and the weight of the negative electrode active material layer was divided by the negative electrode area to calculate the negative electrode active material layer areal density, which was 44.0 g / m 2 It was.

[0112] [Manufacture of Negative Electrodes 2 to 4] Negative electrodes 2 to 4 were manufactured in the same manner as [Manufacture of Negative Electrode 1], except that the negative electrode active material layer areal density was adjusted as shown in Table 1.

[0113]

Table 1

[0114] [Preparation of Positive Electrode Active Material] The crushed coconut shell carbide was put into a small carbonization furnace and carbonized at 500 °C for 3 hours under a nitrogen atmosphere to obtain a carbide. The obtained carbide was put into an activation furnace, and steam heated in a preheating furnace was introduced into the activation furnace at a rate of 1 kg / h, and the temperature was raised to 900 °C over 8 hours for activation. The carbide after activation was taken out and cooled under a nitrogen atmosphere to obtain activated carbon. The obtained activated carbon was washed with water for 10 hours and then drained, dried in an electric dryer maintained at 115 °C for 10 hours, and then pulverized with a ball mill for 1 hour to obtain Activated Carbon 1. Using a laser diffraction particle size distribution measuring device (SALD-2000J) manufactured by Shimadzu Corporation, the average particle diameter of Activated Carbon 1 was measured, and the result was 5.5 μm. Also, using a pore distribution measuring device (AUTOSORB-1 AS-1-MP) manufactured by Yuasa Ionics, the pore distribution of Activated Carbon 1 was measured. As a result, the BET specific surface area was 2360 m 2 / g, the mesopore volume (V1) was 0.52 cc / g, the micropore volume (V2) was 0.88 cc / g, and V1 / V2 = 0.59.

[0115] [Manufacture of Cathode Precursor 1] Mix 46.200% by mass of activated carbon 1, 2.000% by mass of carboxymethyl cellulose (CMC3), 40.000% by mass of lithium carbonate, 5.000% by mass of carbon black, 4.500% by mass of acrylic latex (LTX), 2.000% by mass of PVP (polyvinyl pyrrolidone), and distilled water so that the mass ratio of the solid content is 34.1% by mass. Disperse this mixture for 20 minutes at a rotational speed of 2000 rpm using a planetary mixer "Awa Toriren Tarou (registered trademark)" manufactured by Shin-Kee Co., Ltd. to obtain a mixture. To the obtained mixture, mix a carbon nanotube (CNT) dispersion liquid so that the carbon nanotube is 0.120% by mass and CMC1 is 0.180% by mass, and disperse it for 10 minutes at a rotational speed of 2,000 rpm to prepare a positive electrode coating liquid 1. The viscosity (ηb) and TI value of the obtained positive electrode coating liquid 1 were measured using an E-type viscometer TVE-35H manufactured by Toki Sangyo Co., Ltd. As a result, the viscosity (ηb) was 2,340 mPa·s and the TI value was 5.1. Also, the degree of dispersion of the obtained positive electrode coating liquid 1 was measured using a particle gauge manufactured by Yoshimitsu Seiki Co., Ltd. As a result, the particle size was 33 μm. Using a doctor blade, coat the positive electrode coating liquid 1 on one side of an aluminum foil with a thickness of 15 μm, dry it for 10 minutes on a hot plate heated to 50 °C, and then press it using a roll press under the conditions of a pressure of 6 kN / cm and a surface temperature of 25 °C of the press part to obtain a positive electrode precursor 1. When the basis weight of the positive electrode precursor 1 was measured in the same manner as above, it was 48.0 g / m 2 It was.

[0116] [Production Examples of Positive Electrode Precursors 2 to 4] Positive electrode precursors 2 to 4 were produced in the same manner as [Production of Positive Electrode Precursor 1], except that the usage amounts of each component were adjusted as shown in Table 2.

[0117]

Table 2

[0118] [Preparation of Electrolyte 1] As an organic solvent, a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 33:67 (volume ratio) was used. As an electrolyte, LiFSI was used, and an electrolyte salt was dissolved to a concentration of 1.0 mol / L to obtain a non-aqueous electrolyte 1.

[0119] [Preparation of Electrolytes 2 - 5] Non-aqueous electrolytes 2 - 5 were produced in the same manner as [Preparation of Electrolyte 1], except that the usage amounts of each component were adjusted as shown in Table 3. [Table 3]

[0120] [Example 1] [Manufacture of Non-aqueous Alkali Metal Storage Element] [Assembly Process] One piece of the obtained positive electrode precursor 1 was cut out so that the positive electrode active material layer was 4.4 cm × 9.4 cm, and the size of the positive electrode current collector part without the positive electrode active material layer was 1.5 cm × 2.5 cm. A polyimide tape with a size of 0.5 cm × 2.5 cm and a thickness of 35 μm was attached from the end of the positive electrode active material layer onto the positive electrode current collector without the positive electrode active material layer. Subsequently, one piece of the negative electrode 1 was cut out so that the negative electrode active material layer was 4.5 cm × 9.5 cm, and the size of the current collector part without the negative electrode active material layer was 1.4 cm × 2.5 cm. Also, one piece of a polyethylene separator (manufactured by Asahi Kasei Corporation, thickness 15 μm) with a size of 4.7 cm × 9.8 cm was prepared. Using these, in the order of the positive electrode precursor 1, the separator, and the negative electrode 1, with the separator in between, they were laminated so that the center of the positive electrode active material layer and the center of the negative electrode active material layer overlapped, and the negative electrode end and the protective layer of the positive electrode current collector overlapped to obtain an electrode laminate. Positive and negative terminals were ultrasonically welded to the obtained electrode body, placed in an outer package formed of an aluminum laminate, and three sides including the electrode terminal part were sealed by heat sealing.

[0121] [Liquid Injection, Impregnation, and Sealing Process] In a dry air environment at atmospheric pressure, a temperature of 25 °C, and a dew point of -40 °C or lower, approximately 2.5 g of non-aqueous electrolyte 1 was injected into the exterior body containing the electrode laminate. Subsequently, the exterior body containing the electrode laminate and the non-aqueous electrolyte was placed in a decompression chamber, decompressed from atmospheric pressure to -87 kPa, then returned to atmospheric pressure, and left standing for 5 minutes. Thereafter, the exterior body in the chamber was decompressed from atmospheric pressure to -87 kPa and then returned to atmospheric pressure, and this process was repeated 4 times, and then left standing at atmospheric pressure for 15 minutes. Through the above process, the non-aqueous electrolyte 1 was impregnated into the electrode laminate. Thereafter, the electrode laminate impregnated with the non-aqueous electrolyte 1 was placed in a vacuum sealing machine, and the exterior body was sealed by sealing at 180 °C for 10 seconds under a pressure of 0.1 MPa in a state of being decompressed to -95 kPa.

[0122] [Alkali metal doping step] Both sides of the center part of the sealed electrode laminate were sandwiched with a buffer material made of silicon sponge of 3.0 cm × 7.0 cm, and pressurized at a pressure of 30 kPa. Initial charging was performed by a method of performing constant current charging at a temperature of 45 °C until the voltage reached 4.5 V at a current value of 10 mA, and then continuing constant voltage charging at 4.5 V for 2 hours, and alkali metal doping was performed on the negative electrode.

[0123] [Aging step] The electrode laminate after alkali metal doping was taken out of the dry box, and constant current discharge was performed at 50 mA until the voltage reached 2.0 V in an environment at 25 °C, and then the voltage was adjusted to 2.0 V by performing constant current discharge at 2.0 V for 1 hour. Subsequently, the electrode laminate sealed in the exterior body was stored in a constant temperature bath at 85 °C for 12 hours.

[0124] [Gas venting step] After aging, in a dry air environment at a temperature of 25°C and a dew point of -40°C, a part of the exterior body was opened and the electrode laminate was taken out. The taken-out electrode laminate was placed in a decompression chamber and decompressed from atmospheric pressure to -80 kPa over 3 minutes using a diaphragm pump, and then the process of returning to atmospheric pressure over 3 minutes was repeated a total of 3 times. Thereafter, the electrode laminate was put back into the exterior body, and using a vacuum sealing machine, after decompressing to -90 kPa, it was sealed at 200°C for 10 seconds at a pressure of 0.1 MPa to seal the exterior body, thereby manufacturing a non-aqueous alkali metal storage element. Also, for the non-aqueous alkali metal storage element, as described in the above item [Calculation methods for A and B], each value was measured or calculated and is shown in Table 4.

[0125] 〈Evaluation of non-aqueous alkali metal storage element〉 [Measurement of internal resistance Ra] The internal resistance Ra (mΩ) is a value obtained by the following method. First, in a thermostatic chamber set at 25°C, the non-aqueous alkali metal storage element is subjected to constant current charging at a current value of 20 C until it reaches 4.0 V, and then constant voltage charging with an applied constant voltage of 4.0 V is performed for a total of 30 minutes. Subsequently, with a sampling interval of 0.05 seconds, constant current discharge is performed at a current value of 20 C until 2.0 V is reached to obtain a discharge curve (time-voltage). In this discharge curve, when the voltage at the time of discharge time = 1 second and 2 seconds is used to extrapolate by linear approximation to obtain the voltage at discharge time = 0 seconds as Eo, the value calculated as Ra = ΔE / (current value of 20 C) from the voltage drop ΔE = 4.0 - Eo. For one of the obtained non-aqueous alkali metal storage elements, in a thermostatic chamber set at 25°C, using a charge-discharge device (5V, 10A) manufactured by Asuka Electronics Co., Ltd., the internal resistance Ra was measured by the above method, and Ra was 80.5 mΩ. This value is shown in Table 5 as the initial internal resistance Ra.

[0126] [Measurement of capacity Qa] The capacity Qa (mAh) is a value obtained by the following method. First, in a thermostatic chamber set at 25°C, the non-aqueous alkali metal storage element is charged at a constant current of 20C until it reaches 4.0V, and then constant voltage charging with an applied constant voltage of 4.0V is performed for a total of 30 minutes. Subsequently, with a sampling interval of 1.0 second, the discharge capacity when discharging at a constant current of 1C until 2.0V is reached is defined as the capacity Qa. For the above non-aqueous alkali metal storage element, in a thermostatic chamber set at 25°C, using a charge-discharge device (5V, 10A) manufactured by Asuka Electronics Co., Ltd., when the capacity Ra was measured by the above method, Qa was 6.58 mAh. This value was shown in Table 5 as the initial capacity Qa.

[0127] [High-temperature and high-voltage cycle test] The change rates of the resistance and capacity after the high-temperature and high-voltage cycle test are values measured by the following method. First, in a thermostatic chamber set at 85°C, the non-aqueous alkali metal storage element and the corresponding cell are charged at a constant current of 50C until it reaches 4.2V, and then discharged at a constant current of 50C until it reaches 3.0V. After repeating this charge-discharge 1000 times, the internal resistance Rb after the high-temperature and high-voltage cycle test is measured according to the above method for measuring the internal resistance, and the capacity Qb after the high-temperature and high-voltage cycle test is measured according to the above method for measuring the capacity. Let Rb / Ra be the resistance change rate after the high-temperature and high-voltage cycle test, and Qb / Qa be the capacity change rate after the high-temperature and high-voltage cycle test. These results are shown in Table 5.

[0128] 《Examples 2 to 11, Comparative Examples 1 to 7》 As the negative electrode, the positive electrode precursor, and the non-aqueous electrolyte, the materials described in Table 1, Table 2, and Table 3 were used respectively, and the manufacturing conditions were as shown in Table 4. Except that polyimide tapes were not attached to the positive electrode current collector parts in Comparative Examples 1 to 4, non-aqueous alkali metal storage elements were manufactured and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 4 and Table 5.

[0129]

Table 4

[0130]

Table 5

[0131] From the comparison between the examples and the comparative examples, by pressing the central part of the non-aqueous alkali metal storage element during alkali metal doping, the decomposition reaction of the alkali metal carbonate in the central part is promoted, and the alkali metal ion concentrations in the outer peripheral part and the central part of the negative electrode can be changed. It is considered that the suppression of the resistance increase and the improvement of the capacity retention rate in the high-temperature and high-voltage cycle can be achieved.

[0132] 《Examples 12 to 17》 A non-aqueous alkali metal storage element was produced and evaluated in the same manner as in Example 1, except that the positive electrode protective layer was as described in Table 6.

[0133] In Examples 14 and 15 where a carbon material was used as the positive electrode protective layer, an anchor foil with an anchor layer coated with a width of 7.0 cm and a thickness of 1 μm on an aluminum foil with a width of 15.0 cm and a thickness of 15 μm was used as the positive electrode current collector. The positive electrode active material layer was coated with a width of 6.0 cm, leaving a 0.5 cm-wide portion where the anchor layer was exposed, to prepare a positive electrode precursor. Subsequently, when cutting out the positive electrode precursor, a non-aqueous alkali metal storage element was produced such that the anchor layer became a protective layer with a size of 0.5 cm × 2.5 cm.

[0134] In Examples 16 and 17 where inorganic fine particles were used as the positive electrode protective layer, an aqueous dispersion solution of 80 parts by mass of inorganic particles, 5 parts by mass of carboxymethyl cellulose, and 15 parts by mass of acrylic latex was applied with a width of 0.5 cm from the end of the positive electrode active material layer of the positive electrode precursor 1 and dried before use.

[0135]

Table 6

[0136] 《Example 18》 On one side of an electrolytic copper foil with a thickness of 10 μm, the negative electrode coating liquid 1 was applied using a doctor blade, and dried for 10 minutes on a hot plate heated to 50°C. Subsequently, the negative electrode coating liquid 1 was applied to the back surface of the electrolytic copper foil and dried in the same manner as above. Next, using a roll press machine, the negative electrode 5 was produced by pressing under the conditions of a pressure of 5 kN / cm and a surface temperature of 25°C in the pressing section.

[0137] Using a doctor blade, the positive electrode coating liquid 1 was applied to one side of an aluminum foil with a thickness of 15 μm, and dried for 10 minutes on a hot plate heated to 50°C. Subsequently, the positive electrode coating liquid 1 was applied to the back surface of the aluminum foil and dried in the same manner as above. By pressing using a roll press machine under the conditions of a pressure of 6 kN / cm and a surface temperature of 25°C in the pressing section, the positive electrode precursor 5 was obtained.

[0138] Polyimide tapes of 0.5 cm × 2.5 cm were attached to both sides of the current collector of the positive electrode precursor 5, and in the order of the negative electrode 5, the same separator as that used in Example 1, the positive electrode precursor 5, the separator, the negative electrode 5, with the separator sandwiched in between, the positive electrode active material layer and the negative electrode active material layer were laminated so as to face each other, and a non-aqueous alkali metal storage element was produced in the same manner as in Example 1 except for obtaining an electrode laminate.

[0139] 《Comparative Example 8》 A negative electrode 6 was produced in the same manner as in Example 18 except that an etched copper foil with a thickness of 12 μm and an aperture ratio of 20% was used. A positive electrode precursor 6 was produced in the same manner as in Example 18 except that an etched aluminum foil with a thickness of 20 μm and an aperture ratio of 20% was used. A non-aqueous alkali metal storage element was produced in the same manner as in Comparative Example 1 except that an electrode laminate was obtained by laminating the negative electrode 6, the separator, the positive electrode precursor 6, the separator, and the negative electrode 6 in this order with the separator sandwiched in between so that the positive electrode active material layer and the negative electrode active material layer faced each other.

[0140] The evaluation results of Example 18 and Comparative Example 8 are shown in Table 7.

[0141]

Table 7

[0142] In Comparative Example 8, by using an etched foil having openings as the current collector foil, the outermost negative electrode active material layer was also uniformly doped with alkali metal ions. As a result, the potential of the outermost negative electrode active material layer decreased, and the reaction with the excess non-aqueous electrolyte outside the electrode body became likely to occur, leading to an increase in resistance and a decrease in the capacity retention rate during high-temperature and high-voltage cycles.

Industrial Applicability

[0143] The non-aqueous alkali metal storage element of the present invention can be suitably used as a non-aqueous alkali metal storage element used in a power regeneration system of a hybrid drive system of an automobile, a power load leveling system in natural power generation such as solar power generation and wind power generation or a microgrid, an uninterruptible power supply system in a factory production facility, a non-contact power supply system for the purpose of leveling voltage fluctuations and storing energy such as microwave power transmission and electrolytic resonance, and an energy harvesting system for the purpose of using power generated by vibration power generation or the like, which requires high durability in a high-temperature and high-voltage environment. For example, a plurality of non-aqueous alkali metal storage elements can be connected in series or in parallel to form a storage module. The non-aqueous alkali metal storage element of the present invention is preferable because the effects of the present invention are maximally exhibited when applied as a lithium-ion capacitor.

Explanation of Reference Numerals

[0144] E Electrode body 1 Negative electrode 2 Negative electrode current collector 3 Negative electrode active material layer 4 Separator 5 Positive electrode 6 Positive electrode current collector 7 Positive electrode active material layer 8 Protective layer 9 Non-protective layer c Central portion of negative electrode e End portion of negative electrode о Outer peripheral portion of negative electrode

Claims

1. A non-aqueous alkali metal storage element comprising a positive electrode including a positive electrode active material layer disposed on a positive electrode current collector, a negative electrode including a negative electrode active material layer disposed on a negative electrode current collector, and a separator, and a non-aqueous electrolyte containing an alkali metal ion, wherein the positive electrode active material layer contains a positive electrode active material containing a carbon material and an alkali metal carbonate, the concentration of bis(fluorosulfonyl)imide ion contained in the non-aqueous electrolyte is 0.97 mol / L or more, and the concentration of hexafluorophosphate ion is 0.00 mol / L or more and 0.05 mol / L or less, the positive electrode has a protective layer and a non-protective layer on the positive electrode current collector, on the projection plane in the stacking direction of the electrode body, the protective layer and the negative electrode end overlap, and when the alkali metal ion concentration per unit area of the outer peripheral portion of the negative electrode is A (mAh / g) and the alkali metal ion concentration per unit area of the central portion is B (mAh / g), 1.02 ≦ B / A ≦ 1.

45.

2. The non-aqueous alkali metal storage element according to Claim 1, wherein the protective layer exists on both surfaces of the positive electrode.

3. The negative electrode has the negative electrode active material layer on both surfaces of the negative electrode current collector, the outermost layer of the electrode body is the negative electrode, and when the alkali metal ion concentration per unit area of the central portion of the negative electrode active material layer that does not face the positive electrode is E (mAh / g), B > E. The non-aqueous alkali metal storage element according to Claim 1 or 2.

4. The protective layer is a protective tape, and the base material of the protective tape is at least one material selected from the group consisting of polyether ketone, polyphenylene sulfide, polyethylene terephthalate, polyethylene naphthalate, polyamide, polyimide, aramid, acetate cloth, and polytetrafluoroethylene tape. The non-aqueous alkali metal storage element according to any one of Claims 1 to 3.

5. The non-aqueous alkali metal storage element according to any one of Claims 1 to 4, wherein the protective layer contains at least one carbon material selected from the group consisting of carbon black, graphite, graphene, and carbon nanotubes.

6. The non-aqueous alkali metal storage element according to any one of Claims 1 to 5, wherein the protective layer contains inorganic fine particles.

7. The non-aqueous alkali metal power storage element according to any one of claims 1 to 6, wherein the positive electrode and / or the negative electrode contains carbon nanotubes.

8. A power storage module including the non-aqueous alkali metal power storage element according to any one of claims 1 to 7.

9. The power storage module according to claim 8, wherein the power storage module is incorporated into at least one system selected from the group consisting of a power regeneration assist system, a power load leveling system, an uninterruptible power supply system, a non-contact power supply system, an energy harvesting system, a power storage system, a solar power generation power storage system, an electric power steering system, an emergency power supply system, an in-wheel motor system, an idle stop system, an electric vehicle, a plug-in hybrid vehicle, a hybrid vehicle, an electric motorcycle, a rapid charging system, and a smart grid system.

10. A non-aqueous alkali metal power storage element according to any one of claims 1 to 7, a lead battery, a nickel-hydrogen battery, a lithium-ion secondary battery, or a fuel cell is connected in series or parallel to form a power storage system.

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