JP2022142971A - positive electrode precursor - Google Patents

Abstract

To provide a positive electrode precursor capable of providing a non-aqueous alkali metal storage element having high stability and high capacity and promoting decomposition of an alkali metal compound.SOLUTION: A positive electrode precursor includes a positive electrode active material containing a carbon material, a coal oxide, and an alkali metal compound other than the positive electrode active material. The positive electrode precursor includes a positive electrode current collector, and a positive electrode active material layer containing the positive electrode active material and the coal oxide and provided on one or both sides of the positive electrode current collector. At least a part of the surface of the positive electrode active material and at least a part of the surface of the alkali metal compound are coated with the coal oxide.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to positive electrode precursors.

In recent years, from the viewpoint of effective use of energy aiming at conservation of the global environment and resource saving, power smoothing systems for wind power generation, late-night power storage systems, household distributed power storage systems based on solar power generation technology, and power storage for electric vehicles. systems are attracting attention. A primary requirement for batteries used in these power storage systems is high energy density. As a leading candidate for high energy density batteries that can meet such demands, the development of lithium ion batteries is being vigorously pursued. The second requirement is high output characteristics. For example, in a combination of a high-efficiency engine and an energy storage system (e.g., hybrid electric vehicle) or a combination of a fuel cell and an energy storage system (e.g., fuel cell electric vehicle), there is a demand for an energy storage system that exhibits high output discharge characteristics during acceleration. It is Currently, electric double layer capacitors, nickel-metal hydride batteries, and the like are being developed as high-power storage devices.

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

Nickel-metal hydride batteries, which are currently commonly used in hybrid electric vehicles, have a high output equivalent to that of electric double layer capacitors and an energy density of about 160 Wh/L. However, research is being vigorously pursued to further increase its energy density and output characteristics, as well as its durability (in particular, stability at high temperatures).

Also in lithium-ion batteries, research is being carried out toward higher output. For example, a lithium-ion battery has been developed that provides a high output exceeding 3 kW/L at a depth of discharge (that is, the ratio (%) of the amount of discharge to the discharge capacity of the storage element) of 50%. However, the energy density is 100 Wh/L or less, and the design deliberately suppresses the high energy density, which is the greatest feature of lithium-ion batteries. In addition, its durability (cycle characteristics and high-temperature storage characteristics) is inferior to that of electric double layer capacitors. used in a narrower range than the range of Since the capacity of lithium-ion batteries that can actually be used is even smaller, research to further improve the durability is being vigorously pursued.

As described above, there is a strong demand for practical use of an electric storage device having high energy density, high output characteristics, and high durability. However, since the existing electric storage elements described above each have advantages and disadvantages, there is a demand for new electric storage elements that satisfy these technical requirements. As a promising candidate, an electric storage element called a lithium ion capacitor has attracted attention and is being actively developed. Lithium ion capacitors are a type of energy storage device that uses a non-aqueous electrolyte solution containing lithium salt (hereinafter also referred to as a "non-aqueous alkali metal energy storage device"). It is a storage element that charges and discharges by a non-Faraday reaction due to the adsorption and desorption of anions as in the case of a lithium ion battery, and by a Faraday reaction due to the absorption and release of lithium ions at the negative electrode as in a lithium ion battery.

Summarizing the electrode materials and their characteristics generally used in the above storage devices, materials such as activated carbon are generally used for the electrodes, and charge and discharge are performed by the adsorption and desorption (non-Faraday reaction) of ions on the surface of the activated carbon. When it is carried out, high output and high durability are obtained, but the energy density becomes low (for example, 1 time). On the other hand, when an oxide or carbon material is used for the electrodes and charge and discharge are performed by faradaic reaction, the energy density is high (for example, 10 times that of non-faradaic reaction using activated carbon), but durability and output There is a problem with the characteristics.

As a combination of these electrode materials, the electric double layer capacitor uses activated carbon (one energy density) for the positive and negative electrodes, and is characterized in that both the positive and negative electrodes are charged and discharged by non-Faraday reactions, and therefore have high output and high durability. However, the energy density is low (one time positive electrode x one time negative electrode = 1).

Lithium ion secondary batteries are characterized by using a lithium transition metal oxide (10 times the energy density) for the positive electrode and a carbon material (10 times the energy density) for the negative electrode, and charging and discharging both the positive and negative electrodes by the Faraday reaction. It has a high energy density (10 times the positive electrode × 10 times the negative electrode = 100), but there are problems with the output characteristics and durability. Furthermore, in order to satisfy the high durability required for hybrid electric vehicles and the like, the depth of discharge must be limited, and lithium ion secondary batteries can only use 10 to 50% of that energy.

Lithium ion capacitors are characterized by using activated carbon (1 times the energy density) for the positive electrode and a carbon material (10 times the energy density) for the negative electrode, and charging and discharging by non-faradaic reaction at the positive electrode and faradaic reaction at the negative electrode. It is an asymmetric capacitor that combines the characteristics of an electric double layer capacitor and a lithium ion secondary battery. Lithium-ion capacitors have high output and high durability, but also have high energy density (1 times positive electrode × 10 times negative electrode = 10), and there is no need to limit the depth of discharge like lithium-ion secondary batteries. It is a feature.

Various studies have been conducted to further increase the capacity of the lithium ion capacitor and develop new carbon materials (Patent Documents 1 to 3, Non-Patent Document 1). Patent Document 1 discloses a lithium ion capacitor containing activated carbon and graphene oxide (GO), and the binding force between the active material particles can be increased by subjecting the graphene oxide in the positive electrode active material layer to reduction treatment. can. Patent Document 2 proposes a positive electrode precursor that promotes decomposition of an alkali metal compound contained in the positive electrode precursor and has high capacity and high output. Patent Document 3 discloses the use of coal oxide (CO), which exhibits excellent proton conductivity even at high temperatures of 100° C. or higher and does not exhibit electronic conductivity, as a solid electrolyte membrane. Non-Patent Document 1 discloses that a functional group such as a carbonyl group on carbon reacts with lithium ions to develop a pseudocapacity.

JP 2013-47171 A WO2017/126687 JP 2017-52667 A

Bor Z. Jag, Chenguang Liu, David Neff, Zhenning Yu, Ming C.; Wang, Wei Xiong, Aruna Zhamu Nano Lett. , 2011, 11, 3785-3791 E. P. Barrett, L.; G. Joyner andP. Halenda, J.; Am. Chem. Soc. , 73, 373 (1951) B. C. Lippens, J.; H. de Boer, J.; Catalysis, 4319 (1965) R. S. Mikhail, S.; Brunauer, E.; E. Bodor, J.; Colloid Interface Sci. , 26, 45 (1968)

However, since graphene oxide contains many epoxy groups with low thermal stability, the functional groups are reductively decomposed in an environment of 100° C. or higher. Therefore, when activated carbon and graphene oxide are mixed to improve energy density, vacuum drying in a high temperature environment of 100 ° C. or higher to remove moisture in the activated carbon decomposes the functional groups of graphene oxide, which prevents high capacity. Can not. Further, there is room for improvement in increasing the capacity by using oxidized coal in combination with activated carbon, and in the decomposition efficiency of alkali metal compounds when oxidized coal is used in combination with alkali metal compounds.

An object of the present disclosure is to provide a positive electrode precursor that can provide a non-aqueous alkali metal storage element that has high thermal stability, high capacity, and accelerates the decomposition of alkali metal compounds.

Examples of embodiments of the present disclosure are listed below.
[1]
A positive electrode precursor comprising a positive electrode active material containing a carbon material, coal oxide, and an alkali metal compound other than the positive electrode active material,
The positive electrode precursor has a positive electrode current collector and a positive electrode active material layer containing the positive electrode active material and the coal oxide provided on one or both sides of the positive electrode current collector,
A positive electrode precursor, wherein at least part of the surface of the positive electrode active material and at least part of the surface of the alkali metal compound are coated with the coal oxide.
[2]
The content of the coal oxide contained in the positive electrode active material layer of the positive electrode precursor is 0.5% by mass or more and 8.0% by mass or less based on the total mass of the positive electrode active material layer, and the alkali metal The positive electrode precursor according to item 1, wherein the content of the compound is 20.0% by mass or more and 45.0% by mass or less based on the total mass of the positive electrode active material layer.
[3]
The carboxyl group functional group content of the oxidized coal measured by XPS (X-ray photoelectron spectroscopy) is 10.0 atm% or more and 26.0 atm% or less, and the epoxy group functional group content is 0.1 atm% or more and 8.0 atm%. The positive electrode precursor according to item 1 or 2, which is:
[4]
4. The positive electrode precursor according to any one of items 1 to 3, wherein the oxidized coal has a sheet size of 10 nm or more and less than 50 nm as measured by an AFM (atomic force microscope).

According to the present disclosure, there is provided a positive electrode precursor capable of providing a non-aqueous alkali metal storage element that has high temperature stability of 100° C. or higher, high capacity, and accelerates the decomposition of alkali metal compounds. .

FIG. 1 is an AFM image of oxidized coal in an example. FIG. 2 is an XPS spectrum of oxidized coal in the example. FIG. 3 is an XPS spectrum of graphene oxide in a comparative example. FIG. 4 is an SeM image of the positive electrode precursor 1 in Example 1 taken at a magnification of 5,000. FIG. 5 is an SeM image of the positive electrode precursor 5 in Comparative Example 1 taken at a magnification of 5,000. FIG. 6 is an SeM image of the positive electrode precursor 6 in Comparative Example 2 taken at a magnification of 5,000.

《Non-aqueous alkali metal storage device》
A non-aqueous alkali metal storage element generally includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolytic solution as main components. As the non-aqueous electrolytic solution, a solution in which alkali metal ions are dissolved in an organic solvent is used.

<Positive electrode precursor (positive electrode)>
As will be described later, the negative electrode is pre-doped with alkali metal ions in the process of assembling the non-aqueous alkali metal storage element. In this specification, the positive electrode before the alkali metal doping step is defined as a “positive electrode precursor”, and the positive electrode after the alkali metal doping step is defined as a “positive electrode”.

A positive electrode precursor of the present disclosure includes a positive electrode active material containing a carbon material, coal oxide, and an alkali metal compound other than the positive electrode active material. At least part of the surface of the positive electrode active material and at least part of the surface of the alkali metal compound are coated with coal oxide. The positive electrode after the alkali metal doping step contains a positive electrode active material containing a carbon material and coal oxide, and in addition to these, may further contain an alkali metal compound.

[Positive electrode active material layer]
In the positive electrode current collector and the positive electrode, the positive electrode active material layer contains a positive electrode active material containing a carbon material and coal oxide. In addition to these, the positive electrode active material layer may contain optional components described later, if necessary.

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

When activated carbon is used as the positive electrode active material, there are no particular restrictions on the type of activated carbon and its raw material. preferable. Specifically, V ₁ (cm ³ /g) is the amount of mesopores derived from pores with a diameter of 20 Å or more and 500 Å or less calculated by the BJH method, and micropores derived from pores with a diameter of less than 20 Å calculated by the MP method. When the amount is V ₂ (cm ³ /g),
(1) For high input/output characteristics, 0.3<V ₁ ≤ 0.8 and 0.5 ≤ V ₂ ≤ 1.0 are satisfied, and the specific surface area measured by the BET method is 1, Activated carbon having a density of 500 m ² /g or more and 3,000 m ² /g or less (hereinafter also referred to as activated carbon 1) is preferable, and
(2) In order to obtain a high energy density, 0.8<V ₁ ≤ 2.5 and 0.8<V ₂ ≤ 3.0 are satisfied, and the specific surface area measured by the BET method is 2, Activated carbon having a density of 300 m ² /g or more and 4,000 m ² /g or less (hereinafter also referred to as activated carbon 2) is preferable.

The BET specific surface area, mesopore volume, micropore volume, and average pore diameter of the active material are values obtained by the following methods. The sample is vacuum-dried at 200° C. for a day and night, and the adsorption and desorption isotherms are measured using nitrogen as an adsorbate. Using the adsorption-side isotherm obtained here, the BET specific surface area is calculated by the BET multi-point method or the BET single-point method, the mesopore content is calculated by the BJH method, and the micropore content is calculated by the MP method. The BJH method is a calculation method generally used for analyzing mesopores, and was proposed by Barrett, Joyner, Halenda et al. (Non-Patent Document 1). The MP method means a method for determining micropore volume, micropore area, and micropore distribution using the "t-plot method" (Non-Patent Document 2). S. This is a method devised by Mikhail, Brunauer, and Bodor (Non-Patent Document 3). In addition, the average pore diameter is obtained by measuring each equilibrium adsorption amount of nitrogen gas under each relative pressure at liquid nitrogen temperature, and the total pore volume per mass of the sample is divided by the BET specific surface area. point to what you asked for.

(Activated carbon 1)
The mesopore volume V ₁ of the activated carbon 1 is preferably larger than 0.3 cm ³ /g from the viewpoint of increasing the input/output characteristics when the positive electrode material is incorporated in a power storage device. V ₁ is preferably 0.8 cm ³ /g or less from the viewpoint of suppressing a decrease in the bulk density of the positive electrode. V ₁ is more preferably 0.35 cm ³ /g or more and 0.7 cm ³ /g or less, and still more preferably 0.4 cm ³ /g or more and 0.6 cm ³ /g or less. The micropore volume V2 of the activated carbon ^{1 is preferably 0.5 cm 3} _/ g or more in order to increase the specific surface area of the activated carbon and increase its capacity. V ₂ is preferably 1.0 cm ³ /g or less from the viewpoint of suppressing the bulk of activated carbon, increasing the density as an electrode, and increasing the capacity per unit volume. V ₂ is more preferably 0.6 cm ³ /g or more and 1.0 cm ³ /g or less, and still more preferably 0.8 cm ³ /g or more and 1.0 cm ³ /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, V ₁ /V ₂ is preferably 0.3 or more from the viewpoint of increasing the ratio of the mesopore volume to the micropore volume to the extent that deterioration in output characteristics can be suppressed while maintaining a high capacity. preferable. On the other hand, V ₁ /V ₂ should be 0.9 or less from the viewpoint of increasing the ratio of the amount of micropores to the amount of mesopores to the extent that a decrease in capacity can be suppressed while maintaining high output characteristics. is preferred. A more preferable range of V ₁ /V ₂ is 0.4≦V ₁ /V ₂ ≦0.7, and a further preferable range of V ₁ /V ₂ is 0.55≦V ₁ /V ₂ ≦0.7.

The average pore diameter of the activated carbon 1 is preferably 17 Å or more, more preferably 18 Å or more, and most preferably 20 Å or more, from the viewpoint of maximizing the output of the obtained electricity storage device. Moreover, from the viewpoint of maximizing the capacity, the average pore diameter of the 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 2} /g or more, it is easy to obtain a good energy density. Since it is not necessary to add a large amount of binder, the performance per electrode volume is improved.

Activated carbon 1 having the characteristics described above can be obtained, for example, using the raw materials and processing methods described below. A carbon source used as a raw material of the activated carbon 1 is not particularly limited. For example, plant materials such as wood, wood flour, coconut shells, by-products of pulp manufacturing, bagasse, blackstrap molasses; Fossil-based raw materials: 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; polybutylene, polybutadiene, polychloroprene, etc. synthetic rubber; other synthetic woods, synthetic pulps, etc., and charcoalized products thereof. Among these raw materials, plant-based raw materials such as coconut shells and wood flour, and their carbonized materials are preferable, and coconut shell carbonized materials are particularly preferable, from the viewpoint of mass production and cost.

As the method of carbonization and activation for making these raw materials into the activated carbon 1, known methods such as a fixed bed method, a moving bed method, a fluidized bed method, a slurry method, a rotary kiln method, and the like can be adopted. Carbonization of these raw materials includes inert gases such as nitrogen, carbon dioxide, helium, argon, xenon, neon, carbon monoxide, combustion exhaust gas, etc., or other gases containing these inert gases as main components. A mixed gas may be used to bake at about 400 to 700° C. (preferably 450 to 600° C.) for about 30 minutes to 10 hours. As a method for activating the carbide obtained by the above-described carbonization method, a gas activation method of firing using an activation gas such as water vapor, carbon dioxide, or oxygen is preferably used. Among these, the method using water vapor or carbon dioxide as the activating gas is preferred. In this activation method, the resulting charcoal is heated for 3 to 12 hours (preferably 5 11 hours, more preferably 6 to 10 hours), the temperature is raised to 800 to 1,000° C. for activation. Furthermore, the carbide may be preliminarily activated prior to the above-described activation treatment of the carbide. In this primary activation, a method of calcining the carbon material at a temperature of less than 900° C. using an activating gas such as steam, carbon dioxide, or oxygen to activate the gas is preferably employed. Activated carbon 1 can be produced by appropriately combining the firing temperature and firing time in the carbonization method described above with the activation gas supply rate, temperature increase rate, and maximum activation temperature in the activation method.

The average particle size of activated carbon 1 is preferably 2 to 20 μm. When the average particle size is 2 μm or more, the density of the active material layer is high, so the capacity per electrode volume tends to be high. Incidentally, when the average particle size is small, there is a case where the drawback of low durability is caused, but if the average particle size is 2 μm or more, such a drawback hardly occurs. On the other hand, when the average particle size is 20 μm or less, there is a tendency that it is easily suitable for high-speed charging and discharging. The average particle size of the activated carbon 1 is more preferably 2-15 μm, more preferably 3-10 μm.

(Activated carbon 2)
The mesopore volume V1 of the activated carbon ₂ is preferably a value larger than 0.8 cm ³ /g from the viewpoint of increasing the output characteristics when the positive electrode material is incorporated in a power storage device. V ₁ is preferably 2.5 cm ³ /g or less from the viewpoint of suppressing a decrease in capacity of the storage element. V ₁ is more preferably 1.00 cm ³ /g or more and 2.0 cm 3 /g or less, and still more preferably 1.2 cm ³ /g or more and 1.8 cm ³ /g or less. The micropore volume V2 of the activated carbon ₂ is preferably greater than 0.8 cm3/g in order to increase the specific surface area of the activated carbon and increase its capacity. V ₂ is preferably 3.0 cm ³ /g or less from the viewpoint of increasing the density of the activated carbon as an electrode and increasing the capacity per unit volume. V ₂ is more preferably greater than 1.0 cm ³ /g and less than or equal to 2.5 cm ³ /g, still more preferably greater than or equal to 1.5 cm ³ /g and less than or equal to 2.5 cm ³ /g. The activated carbon 2 having the mesopore volume and micropore volume described above has a higher BET specific surface area than activated carbon used for conventional electric double layer capacitors or lithium ion capacitors. A specific value of the BET specific surface area of the activated carbon 2 is preferably 2,300 m ² /g or more and 4,000 m ² /g or less, and is 3,000 m ² /g or more and 4,000 m ² /g or less. is more preferable, and 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, good energy density is easily obtained, and when the BET specific surface area is 4,000 m ² /g or less, binding is required to maintain the strength of the electrode. Since it is not necessary to add a large amount of agent, the performance per electrode volume is increased.

The activated carbon 2 having the characteristics described above can be obtained, for example, using raw materials and processing 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 that is usually used as a raw material for activated carbon. Examples include plant materials such as wood, wood flour, and coconut shells; Fossil raw materials such as coke; various synthetic resins such as phenol resin, furan resin, vinyl chloride resin, vinyl acetate resin, melamine resin, urea resin, resorcinol resin, and the like. Among these raw materials, phenolic resins and furan resins are particularly preferred because they are suitable for producing activated carbon with a high specific surface area.

Methods for carbonizing these raw materials or methods for heating during activation include, for example, 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 containing these inert gases as main components and mixed with other gases is used. Generally, the carbonization temperature is about 400 to 700° C. and the firing is performed for about 0.5 to 10 hours. As a method for activating carbide, there are a gas activation method in which activating gas such as water vapor, carbon dioxide, and oxygen is used to calcine, and an alkali metal activation method in which heat treatment is performed after mixing with an alkali metal compound. The alkali metal activation method is preferred for producing activated carbon. In this activation method, the mass ratio of the carbide and the 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 greater than the amount of the carbide). After that, heating may be performed for 0.5 to 5 hours in the range of 600 to 900° C. in an inert gas atmosphere, after which the alkali metal compound may be washed off with acid and water, and dried. In order to increase the amount of micropores and not increase the amount of mesopores, it is preferable to increase the amount of carbide and mix it with KOH during activation. To increase both the micropore volume and the mesopore volume, a larger amount of KOH should be used. In order to mainly increase the mesopore volume, it is preferable to perform steam activation after performing alkali activation treatment. The average particle size of the activated carbon 2 is preferably 2 μm or more and 20 μm or less. More preferably, it is 3 μm or more and 10 μm or less.

(Mode of use of activated carbon)
Each of the activated carbons 1 and 2 may be one kind of activated carbon, or a mixture of two or more kinds of activated carbons, and the mixture as a whole may exhibit the respective characteristic values described above. As for the activated carbons 1 and 2, either one of them may be selected and used, or a mixture of the two may be used. The positive electrode active material is a material other than activated carbon ₁ and ₂ (e.g., activated carbon that does not have the specific V1 and/or V2 described above, or a material other than activated carbon (e.g., conductive polymer, etc.)). may include 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, high temperature durability and high voltage durability can be improved.

(lithium transition metal oxide)
The positive electrode active material layer preferably further contains a lithium transition metal compound. By containing the lithium transition metal oxide, the capacity of the non-aqueous alkali metal storage element can be increased. Lithium transition metal oxides include transition metal oxides capable of intercalating and deintercalating lithium. The transition metal oxide used as the positive electrode active material is not particularly limited. Examples of transition metal oxides 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 CoO ₂ {wherein x satisfies 0≦x≦1. },
Li _x NiO ₂ {wherein x satisfies 0≦x≦1. },
Li _x Ni _y M _(1-y) O ₂ {wherein M is at least one element selected from the group consisting of Co, Mn, Al, Fe, Mg, and Ti, and x is 0≦x ≦1 and y satisfies 0.05<y<0.97. },
Li _x Ni _1/3 Co _1/3 Mn _1/3 O ₂ {wherein x satisfies 0≦x≦1. },
Li _x MnO ₂ {wherein x satisfies 0≦x≦1. },
α-Li _x FeO ₂ {wherein x satisfies 0≦x≦1. },
Li _x VO ₂ {wherein x satisfies 0≦x≦1. },
Li _x CrO ₂ {wherein x satisfies 0≦x≦1. },
Li _x FePO ₄ {wherein x satisfies 0≦x≦1. },
Li _x MnPO ₄ {wherein x satisfies 0≦x≦1. },
Li _z V ₂ (PO ₄ ) ₃ {wherein z satisfies 0≦z≦3. },
Li _x Mn ₂ O ₄ {wherein x satisfies 0≦x≦1. },
Li _x M _y Mn _(2-y) O ₄ {wherein M is at least one element selected from the group consisting of Co, Mn, Al, Fe, Mg, and Ti, and x is 0≦x ≦1 and y satisfies 0.05<y<0.97. },
Li _x Ni _a Co _b Al _(1-ab) O ₂ {wherein x satisfies 0≦x≦1, and a and b are 0.02<a<0.97 and 0.02<b < 0.97. },
Li _x Ni _c Co _d Mn _(1-cd) O ₂ {wherein x satisfies 0≦x≦1, and c and d are 0.02<c<0.97 and 0.02<d < 0.97. }
Compounds represented by and the like. Among these, Li _x Ni _a Co _b Al _(1-ab) O ₂ of the above formula is used from the viewpoint of high capacity, low resistance, cycle characteristics, decomposition of alkali metal compounds, and suppression of loss of the positive electrode active material during pre-doping. , _{LixNicCodMn ( 1-cd) O2 , LixCoO2 , LixMn2O4} , _{or LixFePO4} , _{LixMnPO4 , and LizV2 ( PO4 ) 3} The compounds represented are preferred.

If an alkali metal compound different from the positive electrode active material is contained in the positive electrode precursor, the alkali metal compound becomes an alkali metal dopant source during pre-doping, and the negative electrode can be pre-doped. Electrochemical charging/discharging can be performed as a non-aqueous alkali metal storage element even if it is not (that is, x=0 or z=0). 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 capacity of the non-aqueous alkali metal storage element can be increased. When the content of the lithium transition metal oxide is 30.0% by mass or less, the resistance of the non-aqueous alkali metal storage element can be reduced.

(oxidized coal)
Oxidized coal is a carbon material obtained by oxidizing coal. Coal is classified into lignite, sub-bituminous coal, bituminous coal, and anthracite according to the degree of progress of coalification, and anthracite is more preferably used. Anthracite is the most advanced form of coalification, but the classification criteria and names vary depending on the degree of coalification depending on the country. In the present specification, classification of coal shall comply with JIS, and anthracite coal in particular follows the definition of JIS M1002. Oxidized coal is characterized by mainly containing carboxyl groups and less epoxy groups. The oxidized coal does not exhibit electrical conductivity even after heat treatment at 100°C to 200°C.

(graphene oxide)
Graphene oxide is a carbon material obtained by oxidizing graphene or graphite. Graphene is a carbon material in which carbon atoms form a skeleton of a two-dimensional sheet structure, and is classified into monolayer graphene for a single layer and multilayer graphene for a multilayer graphene. Graphite is classified into natural graphite and artificial graphite. In general, graphene oxide is synthesized by oxidizing graphite by the Hummers method using a strong acid aqueous solution such as sulfuric acid, and then separating and purifying the graphite. A feature of this oxidation process is that many epoxy groups are generated as oxygen-containing functional groups on the edge surface of graphene. Since the epoxy group has low thermal stability, oxygen is eliminated by applying heat of 100° C. or higher or by electrochemical reduction, resulting in reduced graphene oxide (RGO). RGO is characterized by exhibiting high electron conductivity because carbon is bonded by sp2 bonds, and is a carbon material different from oxidized coal.

The content of coal oxide in the positive electrode active material layer is preferably 0.5% by mass or more and 8.0% by mass or less, more preferably 1.0% by mass, based on the total mass of the positive electrode active material layer. 6.0% by mass or more, and particularly preferably 2.0% by mass or more and 5.0% by mass or less. If the content of coal oxide in the positive electrode active material layer is 0.5 or more, the capacity of the non-aqueous alkali metal storage element can be increased. If the content of the coal oxide in the positive electrode active material layer is 8.0 or less, the aggregation of the coal oxide can be suppressed and the surface of the positive electrode active material can be prevented from being excessively coated, thereby increasing the capacity.

Coal oxide coats at least part of the surface of the positive electrode active material and at least part of the surface of the alkali metal compound in the positive electrode precursor. By coating the surface of the positive electrode active material with the coal oxide, the carboxyl groups present on the surface of the coal oxide are more likely to react with the alkali metal ions in the electrolytic solution, so that a high-capacity non-aqueous alkali metal storage element can be obtained. can be done. In addition, by coating the surface of the alkali metal compound with the coal oxide, the acidic functional groups such as carboxyl groups present on the surface of the coal oxide promote the decomposition of the alkali metal compound and pre-dope the negative electrode. In the positive electrode after pre-doping, it is preferable that at least part of the surface of the positive electrode active material is coated with coal oxide, and when it is included, at least part of the surface of the alkali metal compound is also coated with coal oxide. preferably.

Oxidized coal can be synthesized, for example, by oxidizing coal using the Hummers method in an aqueous solution containing sodium nitrate, sulfuric acid, potassium permanganate, and oxygen peroxide. The obtained oxidized coal can be washed with an aqueous hydrochloric acid solution and water, and then dried to obtain an oxidized coal powder. A colloidal solution of oxidized coal can be obtained by dissolving the obtained oxidized coal powder in water, irradiating with ultrasonic waves, and then centrifuging to remove insoluble impurities.

The size of oxidized coal can be measured by Topology: Atomic Force Microscopy (AFM) deposited on mica. The sheet size (width) of the oxidized coal is preferably 1 nm or more and 100 nm, more preferably 5 nm or more and 50 nm or less, even more preferably 10 nm or more and less than 50 nm, and particularly 10 nm or more and 30 nm or less. preferable. If the width of the oxidized coal is 1 nm or more, the dispersibility is excellent. If the width is 100 nm or less, the resistance can be lowered by promoting the diffusion of ions. The height of the coal oxide is preferably 0.2 nm or more and 20 nm or less, more preferably 0.4 nm or more and 15 nm or less, and still more preferably 0.6 nm or more and 10 nm or less. If the height is 0.2 nm or more, the dispersibility is excellent. If the height is 20 nm or less, the resistance can be lowered by promoting the diffusion of ions.

Functional groups contained in coal oxide can be measured using X-ray photoelectron spectroscopy (XPS). Regarding the obtained XPS spectrum, the C1s bond energy 285 eV peak is the C-C bond, the 286 eV peak is the C-O bond, the 287 eV peak is the C-O-C bond, and the 289 eV peak is the O=C-O bond. can be attributed as In the oxidized coal in this example, the amount of carboxyl group functional groups assigned at the peak of 289 eV is 10.0 atm% or more and 26.0 atm% or less, and the amount of epoxy group functional groups assigned at the peak of 287 eV is 0.1 atm. % or more and 8.0 atm % or less. If the carboxyl group functional group content is 10.0 atm % or more, the dispersibility in the coating liquid is excellent, and since it functions as an adsorption/desorption site for alkali metal ions, it is possible to increase the capacity of the non-aqueous alkali metal storage element. . If the carboxyl group functional group content is 26.0 atm % or less, the electronic conductivity of the oxidized coal is enhanced, and the output can be increased. If the epoxy group functional group content is 0.1 atm % or more, the dispersibility in the coating liquid can be enhanced. If the epoxy group functional group content is 8.0 atm % or less, functional group decomposition at high temperatures can be suppressed, and thermal stability increases.

In general, epoxy groups and hydroxyl groups tend to form on the basal planes of graphene, and carboxyl groups tend to form on the edges. Graphite and graphene mainly have a developed basal surface, so that epoxy functional groups are likely to be generated by oxidation treatment. Coal, which mainly has an amorphous structure, is likely to generate carboxyl groups by oxidation treatment. This is the difference between oxidized coal and graphene oxide, and is a factor in the high thermal stability (structural stability) of oxidized coal.

(alkali metal compound)
The positive electrode active material layer of the positive electrode precursor of the present disclosure contains an alkali metal compound other than the positive electrode active material. The alkali metal compound can pre-dope the negative electrode by decomposing in the positive electrode precursor to release cations and being reduced at the negative electrode. The alkali metal compound may be included in the positive electrode precursor in any manner. For example, the alkali metal compound may exist between the positive electrode current collector and the positive electrode active material layer, may exist on the surface of the positive electrode active material layer, and may exist in the positive electrode active material layer. The alkali metal compound is preferably contained in the positive electrode active material layer formed on the positive electrode current collector of the positive electrode precursor. In such an embodiment, pre-doping of the negative electrode with alkali metal ions forms pores in the positive electrode active material layer, increasing the effective area of the positive electrode active material layer. The pre-doped positive electrode may also contain the alkali metal compound other than the positive electrode active material.

Examples of such alkali metal compounds include, for example, M being one or more selected from Li, Na, K, Rb, and Cs, oxides such as M ₂ O; hydroxides such as MOH; Examples include halides; carboxylates such as RCOOM (wherein R is H, an alkyl group, or an aryl group), and one or more of these may be used. Specific examples of alkali metal compounds include lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, cesium carbonate, lithium oxide, and lithium hydroxide. As the alkali metal compound, one or more alkali metal carbonates selected from lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, and cesium carbonate are preferably used, and lithium carbonate, sodium carbonate, or potassium carbonate is more preferable. Lithium carbonate is particularly preferably used from the viewpoint that it is preferably used and has a high capacity per unit mass.

The positive electrode precursor may contain at least one alkali metal compound, and the positive electrode precursor may contain Be, Mg, Ca, Sr instead of the above alkali metal compounds or together with the above alkali metal compounds. , and Ba, one or more selected from carbonates, oxides, hydroxides, halides, and carboxylates of alkaline earth metals selected from the group consisting of Ba.

The alkali metal compound, and alkaline earth metal compound if used, is preferably in particulate form. The average particle size of the alkali metal compound is preferably 0.1 μm or more and 10 μm or less. If the average particle size is 0.1 μm or more, the dispersibility in the positive electrode precursor is excellent. If the average particle size is 10 µm or less, the decomposition reaction proceeds efficiently because the surface area of the alkali metal compound increases. Also, the average particle size of the alkali metal compound is preferably smaller than the average particle size of the activated carbon described above. If the average particle size of the alkali metal compound is smaller than the average particle size of the activated carbon, the electron conduction of the positive electrode active material layer is enhanced, which can contribute to the reduction of the resistance of the electrode body or the storage element. Although the method for measuring the average particle size of the alkali metal compound in the positive electrode precursor is not particularly limited, it can be calculated from the SEM image and SEM-EDX image of the cross section of the positive electrode. As for the method for forming the cross section of the positive electrode, BIB processing can be used in which an Ar beam is irradiated from above the positive electrode to form a smooth cross section along the edge of a shielding plate placed directly above the sample. Various methods can be used for making the alkali metal compound into fine particles. For example, pulverizers such as ball mills, bead mills, ring mills, jet mills and rod mills can be used.

The content (% by mass) of the alkali metal compound contained in the positive electrode active material layer of the positive electrode precursor is 20.0% by mass or more and 45.0% by mass when the total mass of the positive electrode active material layer is 100% by mass. The following are preferable. When this value is 20.0% by mass or more, the negative electrode can be pre-doped with a sufficient amount of alkali metal ions, and the capacity of the non-aqueous alkali metal storage element increases. If this value is 45.0% by mass or less, the electron conduction in the positive electrode precursor can be enhanced, so that the alkali metal compound can be efficiently decomposed. When the positive electrode precursor contains two or more alkali metal compounds or alkaline earth metal compounds in addition to the alkali metal compound, the total amount of the alkali metal compounds and alkaline earth metal compounds is within the above range. is preferred. The above alkali metal elements and alkaline earth metal elements can be quantified by ICP-AES, atomic absorption spectrometry, fluorescent X-ray spectrometry, neutron activation spectrometry, ICP-MS, and the like.

(Other Components of Positive Electrode Active Material Layer)
The positive electrode active material layer of the positive electrode precursor in the present invention contains, in addition to the positive electrode active material, coal oxide, and alkali metal compound, if necessary, for example, a dispersant, a conductive filler, a binder, and a pH adjuster. Other ingredients such as agents may be included.

The dispersant is not particularly limited, but is preferably one or more selected from, for example, carboxymethylcellulose, polycarboxylic acid, polycarboxylate, polyvinylpyrrolidone, polyvinyl alcohol, surfactants, and the like. used for It is particularly preferred that the dispersant contains, for example, carboxymethylcellulose and one or more selected from polyvinylpyrrolidone and polyvinyl alcohol. The content of the dispersant 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 positive electrode active material layer of the positive electrode precursor. If the amount of the dispersing agent is 7.0% by mass or less, high input/output characteristics are exhibited without impeding the movement and diffusion of ions into and out of the positive electrode active material.

Examples of binders that can be used include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), fluororubber, polyimide, latex, styrene-butadiene copolymer, and acrylic copolymer. The content of the binder in the positive electrode active material layer of the positive electrode precursor is preferably 0 to 20% by mass, more preferably 0.1 to 15% by mass, relative to 100% by mass of the positive electrode active material.

The conductive filler is preferably made of a conductive carbonaceous material having higher conductivity than the positive electrode active material. As such a conductive filler, for example, one or more selected from carbon black, graphite, graphene, carbon nanotubes, etc., and mixtures thereof are preferable. Examples of carbon black include ketjen black and acetylene black. Examples of graphite include flake graphite. Carbon black is particularly preferably used as the conductive filler. The content of the conductive filler in the positive electrode active material layer of the positive electrode precursor is preferably 25% by mass or less, more preferably 5% by mass or more and 20% by mass or less with respect to 100% by mass of the positive electrode active material. Although it is preferable to mix the conductive filler in the positive electrode active material layer from the viewpoint of increasing the input power, it is preferable to limit the content to 25% by mass or less from the viewpoint of maintaining the energy density per volume of the storage element.

When water is used as a solvent for the coating liquid for forming the positive electrode active material layer, the addition of the alkali metal compound may make the coating liquid alkaline. Therefore, if necessary, a pH adjuster may be added to the coating liquid for forming the positive electrode active material layer. Examples of pH adjusters include, but are not limited to, hydrogen halides such as hydrogen fluoride, hydrogen chloride, and hydrogen bromide; halogen oxo acids such as hypochlorous acid, chlorous acid, and chloric acid; carboxylic acids such as formic acid, acetic acid, citric acid, oxalic acid, lactic acid, maleic acid and fumaric acid; sulfonic acids such as methanesulfonic acid, benzenesulfonic acid and p-toluenesulfonic acid; nitric acid, sulfuric acid, phosphoric acid, boric acid, Acids such as carbon dioxide can be used.

[Positive collector]
The material constituting the positive electrode current collector is not particularly limited 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, but metal foil is preferable. Aluminum foil is more preferable as the positive electrode current collector in the non-aqueous alkali metal storage element. 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, electrolytic deposition, blasting, etc., expanded metal, punched metal, A metal foil having through holes, such as an etched foil, may also be used. From the viewpoint of the alkali metal doping step, which will be described later, non-porous aluminum foil is more preferable, and it is particularly preferable 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. It is preferable to provide an anchor layer containing a conductive material such as graphite, flake graphite, carbon nanotube, graphene, ketjen black, acetylene black, and vapor grown carbon fiber on the surface of the metal foil. By providing the anchor layer, the electrical conductivity between the positive electrode current collector and the positive electrode active material layer is 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.

The thickness of the positive electrode active material layer 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 side, and still more preferably 30 μm or more and 100 μm or less. If this thickness is 10 μm or more, sufficient charge/discharge capacity can be exhibited. On the other hand, if the thickness is 200 μm or less, the ion diffusion resistance in the electrode can be kept low. Therefore, sufficient output characteristics can be obtained, and the cell volume can be reduced, so that the energy density can be increased. The thickness of the positive electrode active material layer when the positive electrode current collector has through-holes or unevenness refers to the average thickness per side of the portion of the positive electrode current collector that does not have through-holes or unevenness.

<Negative electrode>
The negative electrode has a negative electrode current collector and a negative electrode active material layer provided on one side or both sides thereof.

[Negative electrode active material layer]
The negative electrode active material layer contains a negative electrode active material, and in addition thereto, if necessary, may contain optional components such as a dispersant, a conductive filler, and a binder.

(Negative electrode active material)
A material that can occlude and release alkali metal ions can be used as the negative electrode active material. Specific 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 particulate.

The negative electrode active material preferably contains a carbon material. The content 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 of the carbon material can be 100% by mass, but from the viewpoint of obtaining the effect of combined use of other materials, it is preferably 95% by mass or less, and may be 90% by mass or less. The upper limit and lower limit of the carbon material content can be combined arbitrarily.

Examples of carbon materials include non-graphitizable carbon materials; easily graphitizable carbon materials; carbon black; carbon nanoparticles; artificial graphite; natural graphite; Carbonaceous material: Carbonaceous material obtained by heat-treating a carbon precursor such as petroleum pitch, coal pitch, mesocarbon microbeads, coke, synthetic resin (for example, phenolic resin, etc.); furfuryl alcohol resin or novolak Thermal decomposition products of resins; fullerenes; carbon nanofibers; and composite carbon materials thereof.

Among these, from the viewpoint of lowering the resistance of the negative electrode, one or more graphite materials selected from artificial graphite, natural graphite, graphitized mesophase carbon spherules, graphite whiskers, and high specific surface area graphite; pitch, coal-based pitch, mesocarbon microbeads, coke, and synthetic resins, such as phenolic resin, heat treatment in the presence of one or more carbonaceous material precursors, graphite material and a carbonaceous material derived from a carbonaceous material precursor are preferably combined. The carbonaceous material precursor is not particularly limited as long as it can be converted into a carbonaceous material by heat treatment, but petroleum-based pitch or coal-based pitch is particularly preferable. Prior to 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 component generated by volatilization or thermal decomposition of the carbonaceous material precursor used becomes a carbonaceous material, preferably 400° C. or higher and 2,500° C. or lower, more preferably 500° C. or higher. It is 2,000°C or lower, more preferably 550°C or higher and 1,500°C or lower. The atmosphere for the heat treatment is not particularly limited, but a non-oxidizing atmosphere is preferred.

(Other Components of Negative Electrode Active Material Layer)
If necessary, the negative electrode active material layer may contain optional components such as a dispersant, a binder, and a conductive filler in addition to the negative electrode active material. The dispersant, conductive filler, and binder in the negative electrode active material layer are appropriately selected from those exemplified above as the dispersant, conductive filler, and binder in the positive electrode active material layer of the positive electrode precursor, respectively. You can choose to use it. The contents of the dispersant and the binder in the negative electrode active material layer may be within the ranges described above as the contents of the dispersant and the binder in the positive electrode active material of the positive electrode precursor.

[Negative electrode current collector]
The material constituting the negative electrode current collector is preferably a material that has high electronic conductivity and does not deteriorate due to elution into the electrolytic solution or reaction with the electrolyte or ions. For example, metal foil may be used. Such metal foil is not particularly limited, and examples thereof include aluminum foil, copper foil, nickel foil, stainless steel foil and the like. As the negative electrode current collector in the non-aqueous alkali metal storage element, copper foil is preferable when the non-aqueous electrolyte contains lithium ions, and aluminum foil is preferable when the non-aqueous electrolyte contains sodium ions or potassium ions. is preferred. The metal foil as the negative electrode current collector may be a normal metal foil having no unevenness or through-holes, or may be a metal foil having unevenness subjected to embossing, chemical etching, electrolytic deposition, blasting, or the like. , expanded metal, punching metal, etching foil, or other metal foil having through holes may be used. 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.

The thickness of the negative electrode active material layer is preferably 10 μm or more and 100 μm or less, more preferably 15 μm or more and 80 μm or less per side. If this thickness is 10 μm or more, good charge/discharge capacity can be exhibited. On the other hand, if the thickness is 100 μm or less, the cell volume can be reduced and the energy density can be increased. The thickness of the negative electrode active material layer when 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 that does not have holes.

<Separator>
The positive electrode precursor and the negative electrode are laminated with a separator interposed therebetween, or laminated and wound to form an electrode laminate or electrode winding having the positive electrode precursor, the negative electrode and the separator. As the separator, a polyethylene microporous film or polypropylene microporous film used in a lithium ion secondary battery, or a cellulose nonwoven paper used in an electric double layer capacitor, or the like can be used. A film made of organic or inorganic fine particles may be laminated on one side or both sides of these separators. In addition, 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 an internal micro-short tends to decrease. On the other hand, a thickness of 35 μm or less is preferable because it tends to increase the output characteristics of the storage element. Moreover, the thickness of the film made of organic or inorganic fine particles is preferably 1 μm or more and 10 μm or less. A thickness of 1 μm or more is preferable because self-discharge due to internal micro-shorts tends to be reduced. On the other hand, a thickness of 10 μm or less is preferable because it tends to increase the output characteristics of the storage element.

<Exterior body>
A metal can, a laminate film, or the like can be used as the outer package. As the metal can, one made of aluminum is preferable. The metal can may be, for example, rectangular, round, cylindrical, or the like. As the laminate film, a film obtained by laminating a metal foil and a resin film is preferable, and a three-layer structure composed of an outer layer resin film/metal foil/inner resin film is exemplified. The outer layer resin film is for preventing the metal foil from being damaged by contact or the like, and a resin such as nylon or polyester can be suitably used. The metal foil is for preventing the permeation of moisture and gas, and foils of copper, aluminum, stainless steel, etc. can be suitably used. The interior resin film protects the metal foil from the electrolyte to be stored inside and melts and seals the exterior body when heat-sealed, and polyolefin, acid-modified polyolefin, etc. can be suitably used.

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

Examples of electrolyte salts containing alkali metal ions that dissolve in non-aqueous solvents include MFSI, MBF ₄ , MPF ₆ , MClO ₄ , LiB(C ₂ O ₄ ) ₂ , LiBF ₂ (C ₂ O ₄ ), and the like can be used. The non-aqueous electrolyte may contain at least one or more alkali metal ions, may contain two or more alkali metal salts, alkali metal salts and beryllium salts, magnesium salts, calcium salts , strontium salts, and barium salts. When two or more alkali metal salts are contained in the non-aqueous electrolyte, the presence of cations with different Stokes radii in the non-aqueous electrolyte can suppress the increase in viscosity at low temperatures. The low-temperature characteristics of the water-based alkali metal storage element are improved. When alkaline earth metal ions other than the above alkali metal ions are contained in the non-aqueous electrolytic solution, the capacity of the non-aqueous alkaline metal storage element can be increased.

The method of containing two or more alkali metal salts in the non-aqueous electrolytic solution, or the method of containing the alkali metal salt and alkaline earth metal salt in the non-aqueous electrolytic solution is not particularly limited. A method of preliminarily dissolving an alkali metal salt composed of two or more kinds of alkali metal ions in the electrolytic solution, and a method of preliminarily dissolving an alkali metal salt and an alkaline earth metal salt in a non-aqueous electrolytic solution. Further, in the positive electrode precursor, M in the following formula is one or more selected from Li, Na, K, Rb, and Cs,
_Carbonates such as _M2CO3 ;
oxides such as M ₂ O;
hydroxides such as MOH;
Halides such as MF and MCl;
carboxylates such as RCOOM, where R is H, an alkyl group, or an aryl group; and alkaline earth metal carbonates selected from _{BeCO3 , MgCO3 , CaCO3} , SrCO3, or BaCO3, and one or more selected from alkaline earth metal oxides, alkaline earth metal hydroxides, alkaline earth metal halides, alkaline earth metal carboxylates, etc., and pre-dope described later. A method of decomposing in the process and the like are also included.

The electrolyte salt concentration in the electrolytic 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 to maintain proper viscosity and conductivity of the electrolyte. If the non-aqueous electrolyte contains two or more alkali metal salts, or if it contains an alkali metal salt and an alkaline earth metal salt, the total concentration of these salts should be 0.5 mol/L or more. is preferred, and a range of 0.5 to 2.0 mol/L is more preferred.

The amount of water contained in the non-aqueous electrolytic solution is preferably 0 ppm or more and 500 ppm or less. If the water content is 0 ppm or more, the alkali metal compound in the positive electrode precursor can be slightly dissolved, so that pre-doping can be performed under mild conditions, so that the capacity can be increased and the resistance can be decreased. If the water content is 500 ppm or less, decomposition of the electrolyte is suppressed, thereby improving high-temperature storage characteristics. The water content in the electrolytic solution can be measured by the Karl Fischer method described above.

<<Method for producing non-aqueous alkali metal storage element>>
In the non-aqueous alkali metal storage element of the present disclosure, a voltage is applied between the positive electrode precursor and the negative electrode after assembling the storage element using the positive electrode precursor, the negative electrode, the separator, the outer package, and the non-aqueous electrolytic solution. can be manufactured by pre-doping with Each step will be described below.

[Production of positive electrode precursor]
The positive electrode precursor has a positive electrode active material layer on one side or both sides of the positive electrode current collector. In a typical embodiment, the positive electrode active material layer is adhered to the positive electrode current collector. The positive electrode precursor can be produced by known electrode production techniques for lithium ion batteries, electric double layer capacitors, and the like. For example, various materials including a positive 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 applied to one or both sides of the positive electrode current collector. A positive electrode precursor can be obtained by forming a coating film and drying it. Further, the obtained positive electrode precursor may be pressed to adjust the film thickness or bulk density of the positive electrode active material layer.

The method for preparing the coating liquid is not particularly limited, but it is preferable to use a dispersing machine such as a homodisper, a multi-axis dispersing machine, a planetary mixer, a thin-film swirling high-speed mixer, or a rotation-revolution mixer. can be done. In order to obtain a coating liquid in a good dispersed 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. A peripheral speed of 1 m/s or more is preferable because various materials are well dissolved or dispersed. A peripheral speed of 50 m/s or less is preferable because reaggregation is suppressed without destroying various materials due to heat or shear force due to dispersion.

The method of coating the surfaces of the positive electrode active material and the alkali metal compound with coal oxide is not particularly limited. From the viewpoint of more uniform coating, the oxidized coal is dispersed in water in advance to prepare an oxidized coal dispersion, and the positive electrode active material, alkali metal compound, dispersant, binder, etc. A method of adding an oxidized coal dispersion is preferred. The reason for this is that if the oxidized coal is not prepared as an oxidized coal dispersion, aggregation tends to occur, and if the positive electrode active material and the oxidized coal dispersion are mixed first, the oxidized coal is adsorbed on the positive electrode active material. Because there is something.

The degree of dispersion of the coating liquid is preferably such that the particle size measured with a particle gauge is 0.1 μm or more and 100 μm or less. The upper limit of the degree of dispersion is more preferably 80 μm or less, still more preferably 50 μm or less, as a particle size measured with a particle gauge. If the particle size is within this range, the material is not crushed during preparation of the coating liquid, clogging of the nozzle during coating, streaks in the coating film, etc. are suppressed, and stable coating can be achieved.

The viscosity (ηb) of the coating liquid is preferably 100 mPa s or more and 4,000 mPa s or less, more preferably 200 mPa s or more and 2,000 mPa s or less, and still more preferably 300 mPa s or more and 1,500 mPa s or less. is. If the viscosity (ηb) is 100 mPa·s or more, dripping during coating film formation is suppressed, and the coating film width and thickness can be well controlled. Further, when the viscosity is 4,000 mPa·s or less, the dispersibility of the coal oxide in the coating liquid is improved, and the surfaces of the positive electrode active material and the alkali metal storage element can be uniformly coated with the coal oxide.

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.

Formation of the coating film of the positive electrode active material layer is not particularly limited, but a coating machine such as a die coater, a comma coater, a knife coater, or a gravure coating machine can be preferably used. The coating film may be formed by single-layer coating, or may be formed by multi-layer coating. In the case of multi-layer coating, the composition of the coating solution may be adjusted so that the contents of the components in each layer of the coating film are different. When the coating film is applied onto the positive electrode current collector, the coating may be multi-strand coating, intermittent coating, or multi-strand intermittent coating. When the positive electrode active material layer is formed on both sides of the positive electrode current collector, one side of the positive electrode current collector may be coated and dried, and then the other side may be coated and dried sequentially. Both sides of the positive electrode current collector may be simultaneously coated with the coating liquid and dried. In this case, the difference in thickness between the positive electrode active material layers on the front and back surfaces of the positive electrode current collector is preferably 10% or less of the average thickness of both. The closer the mass ratio and film thickness ratio of the positive electrode active material layers on the front and back surfaces to 1.0, the less the charge/discharge load is concentrated on one surface, and the higher the high-load charge/discharge cycle characteristics are.

After forming the coating film of the positive electrode active material layer on the positive electrode current collector, the coating film is dried. The coating film of the positive electrode precursor is preferably dried by an appropriate drying method such as hot air drying or infrared (IR) drying, preferably with far infrared rays, near infrared rays, or hot air. The coating film may be dried at a single temperature, or may be dried by changing the temperature in multiple stages. A plurality of drying methods may be combined for drying. 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 still 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 the temperature is 200° C. or less, cracking of the coating film due to rapid volatilization of the solvent, uneven distribution of the binder due to migration, and oxidation of the positive electrode current collector or the positive electrode active material layer can be suppressed.

The amount of water contained in the dried positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less when the total mass of the positive electrode active material layer is 100% by mass. If the water content is 0.1% by mass or more, the deterioration of the binder due to excessive drying can be suppressed, and the resistance can be lowered. If the water content is 10% by mass or less, the deactivation of alkali metal ions can be suppressed and the capacity can be increased. When N-methyl-2-pyrrolidone (NMP) is used to adjust the coating liquid, the content of NMP in the positive electrode active material layer after drying is, when the total mass of the positive electrode active material layer is 100%, It is preferably 0.1% by mass or more and 10% by mass or less. The amount of water contained in the positive electrode active material layer can be measured, for example, by Karl Fischer titration (JIS 0068 (2001) "Method for measuring water content of chemical products"). The amount of NMP contained in the positive electrode active material layer is obtained by impregnating the positive electrode active material layer with ethanol having a mass 50 to 100 times the mass of the positive electrode active material layer for 24 hours in an environment of 25 ° C., and then extracting NMP by GC. /MS can be measured and quantified based on a calibration curve prepared in advance.

Appropriate press machines such as a hydraulic press machine, a vacuum press machine, and a roll press machine can be suitably used for pressing the positive electrode active material layer. The film thickness, bulk density, and electrode strength of the positive electrode active material layer can be adjusted by the press pressure, the gap between press rolls, and the surface temperature of the press portion, 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 still 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 sufficiently increased. On the other hand, if the pressing pressure is 20 kN/cm or less, the positive electrode precursor does not bend or wrinkle, and the positive electrode active material layer can be adjusted to a desired film thickness or bulk density. When a roll press machine is used for pressing, the gap between the press rolls can be set to an appropriate value so that the positive electrode active material layer has a desired thickness and bulk density. The pressing speed can be set to an appropriate speed at which the positive electrode precursor does not bend or wrinkle.

The surface temperature of the press portion may be room temperature, or may be heated if necessary. The lower limit of the surface temperature of the press part when heating is preferably minus 60° C. of the melting point of the binder used or more, more preferably minus 45° C. or more of the melting point of the binder, and still more preferably minus 30° C. of the melting point of the binder. °C or higher. On the other hand, the upper limit of the surface temperature of the press part when heating is preferably the melting point of the binder used plus 50° C. or less, more preferably the melting point of the binder plus 30° C. or less, and still more preferably the melting point of the binder plus 20°C or less. For example, when polyvinylidene fluoride (melting point 150° C.) is used as the binder, the press part is preferably heated to 90° C. or higher and 200° C. or lower, more preferably 105° C. or higher and 180° C. or lower, and still more preferably 120° C. or higher. It is to heat below 170°C. When a styrene-butadiene copolymer (melting point 100° C.) is used as the binder, the press section is preferably heated to 40° C. or higher and 150° C. or lower, more preferably 55° C. or higher and 130° C. or lower. More preferably, it is heated to 70°C or higher and 120°C or lower. The melting point of the binder can be obtained from the endothermic peak position of DSC (Differential Scanning Calorimetry). For example, using a differential scanning calorimeter "DSC7" manufactured by PerkinElmer, 10 mg of sample resin is set in a measurement cell, and the temperature is increased from 30 ° C. to 250 ° C. at a rate of 10 ° C./min in a nitrogen gas atmosphere. When the temperature is raised, the endothermic peak temperature in the temperature raising process becomes the melting point.

Pressing may be performed multiple times while changing the press pressure, gap, speed, and surface temperature of the press part. When the positive electrode active material layer is coated in multiple lines, slitting is preferably performed before pressing. When the positive electrode precursor is pressed without slitting the negative electrode active material layer coated in multiple lines, excessive stress is applied to the positive electrode current collector portion where the positive electrode active material layer is not coated, causing wrinkles. There is After pressing, the positive electrode active material layer may be slit again.

[Manufacturing of negative electrode]
The negative electrode of the non-aqueous alkali metal storage element can be manufactured by known electrode manufacturing techniques for lithium ion batteries, electric double layer capacitors, and the like. For example, the negative electrode active material 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 on the negative electrode current collector. A negative electrode can be obtained by coating one side or both sides of the polymer to form a coating film and drying it. Further, the obtained negative electrode may be pressed to adjust the film thickness or bulk density of the negative electrode active material layer. The preparation of the coating solution for forming the negative electrode active material layer, the coating of the coating solution on the negative electrode current collector, the drying of the coating film, and the pressing are each carried out according to the method described above for the production of the positive electrode precursor. be able to.

[Assembly process]
In the assembling process, for example, the positive electrode precursor and the negative electrode cut into sheets are laminated via a separator to form a laminate, and the positive electrode terminal and the negative electrode terminal are connected to the electrode laminate to produce the electrode laminate. Alternatively, a positive electrode precursor and a negative electrode may be stacked and wound with a separator interposed between them to form a wound body, 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. A method for connecting the positive electrode terminal and the negative electrode terminal is not particularly limited, but methods such as resistance welding and ultrasonic welding can be used. It is preferable to dry the electrode assembly (electrode laminate or electrode winding assembly) to which the terminals are connected to remove the residual solvent. Although the drying method is not limited, drying can be performed by vacuum drying or the like. The residual solvent is preferably 1.5% by mass or less based on the total mass of the positive electrode active material layer or the negative electrode active material layer. If the residual solvent is more than 1.5% by mass, the solvent remains in the system and deteriorates the self-discharge characteristics, which is not preferable. The dried electrode body is preferably housed in an exterior body typified by a metal can or laminated film in a dry environment with a dew point of −40° C. or less, and has an opening for injecting a non-aqueous electrolyte. It is preferable to leave only one side and seal. If the dew point is higher than −40° C., moisture adheres to the electrode body, remaining in the system, and deteriorating the self-discharge characteristics, which is not preferable. A method for sealing the exterior body is not particularly limited, but methods such as heat sealing and impulse sealing can be used.

[Injection, impregnation, sealing process]
After the assembly process, a non-aqueous electrolytic solution is injected into the electrode body housed in the exterior body. After the injection, it is desirable to further impregnate the positive electrode, the negative electrode, and the separator sufficiently with the non-aqueous electrolytic solution. When at least a part of the positive electrode, the negative electrode, and the separator is not immersed in the electrolytic solution, the alkali metal doping proceeds unevenly in the alkali metal doping step, which will be described later. increases and durability decreases. The method of impregnation is not particularly limited, but for example, the electrode body after injection is placed in a decompression chamber with the exterior body opened, the chamber is decompressed using a vacuum pump, and the pressure is returned to atmospheric pressure. can be used. After the impregnation, it is possible to seal the electrode body in a state where the exterior body is opened while reducing the pressure.

[Alkali metal doping step]
In the alkali metal doping step, a voltage is applied between the positive electrode precursor and the negative electrode to decompose the alkali metal compound preferably contained in the positive electrode precursor to release alkali metal ions, and the alkali metal ions are reduced at the negative electrode. By doing so, it is preferable to pre-dope the negative electrode active material layer with alkali metal ions. In the alkali metal doping step, gas such as CO ₂ is generated with the oxidative decomposition of the alkali metal compound in the positive electrode precursor. Therefore, when applying a voltage, it is preferable to provide means for discharging the generated gas to the outside of the exterior body. As this means, for example, a method of applying a voltage with a part of the exterior body opened; a method of applying a voltage;

[Aging process]
After the alkali metal doping step, the electrode body is preferably aged. In the aging process, the solvent in the electrolytic solution is decomposed on the negative electrode to form a solid polymer film permeable to alkali metal ions on the surface of the negative electrode. The aging method is not particularly limited, but for example, a method of reacting the solvent in the electrolytic solution under a high temperature environment can be used.

[Degassing process]
After the aging step, it is preferable to perform gas venting to ensure that the gas remaining in the electrolyte, positive electrode, and negative electrode is removed. In a state where gas remains in at least part of the electrolyte, the positive electrode, and the negative electrode, ionic conduction is inhibited, and the resistance of the obtained non-aqueous alkali metal storage element increases. The method of degassing is not particularly limited, but for example, a method of placing the electrode assembly in a decompressed chamber with the exterior body open and using a vacuum pump to reduce the pressure in the chamber can be used. After the degassing, the exterior body is sealed by sealing, and the non-aqueous alkali metal storage element can be produced.

<<Use of non-aqueous alkali metal storage element>>
A power storage module can be produced by connecting a plurality of non-aqueous alkali metal power storage elements in series or in parallel. The non-aqueous alkali metal storage element and storage module can achieve both high input/output characteristics and safety at high temperatures. Therefore, power regeneration assist system, power load leveling system, uninterruptible power supply system, contactless power supply system, energy harvesting system, power storage system, solar power generation power storage system, electric power steering system, emergency power supply system, in-wheel motor system , idling stop system, quick charging system, 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 microgrids, and the uninterruptible power supply system is preferably used for factory production equipment. In contactless power supply systems, non-aqueous alkali metal storage elements are used for leveling voltage fluctuations such as microwave power transmission or electric field resonance and storing energy; in energy harvesting systems, non-aqueous alkali metal storage elements are used for vibration power generation. In order to use the electric power generated by etc., it is preferably used respectively.

In an electric storage system, a plurality of non-aqueous alkali metal electric storage elements are connected in series or in parallel as a cell stack, or a non-aqueous alkali metal electric storage element and a lead battery, a nickel hydrogen battery, a lithium ion secondary battery or A fuel cell is connected in series or in parallel. In addition, since non-aqueous alkali metal storage devices can achieve both high input/output characteristics and safety at high temperatures, they are used in vehicles such as electric vehicles, plug-in hybrid vehicles, hybrid vehicles, and electric motorcycles. can 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 installed in the vehicle.

<<Example of production of oxidized coal (CO)>>
Anthracite coal (Sanyo Mining Co., Ltd., Vietnam) produced in mortar was made into coal oxide ₍ CO) using the _Hummers method in _NaNO3 , _H2SO4 , _KMnO4 and _H2O2 solutions. The resulting mixture was washed with 5% HCl solution and distilled water three times and dried at 50°C. The obtained CO powder was suspended in distilled water and irradiated with ultrasonic waves for 2 hours. The suspension was centrifuged to remove insoluble impurities, and the supernatant was collected to obtain a 1.5% by mass oxidized coal dispersion. The obtained sample was heat-treated in a baking machine for 1 hour to prepare a sample for analysis.

[Analysis of oxidized coal]
(Sheet size measurement of oxidized coal using AFM)
For the oxidized coal sample for analysis obtained above, the sheet size of the oxidized coal was measured using an atomic force microscope (manufactured by Bruker, Digital Instruments Nanoscope V). The measurement results are shown in FIG. From FIG. 1, the oxidized coal had a plate-like shape with a width of about 30 nm and a height of about 1 nm.

(Functional group measurement of oxidized coal using XPS)
For the oxidized coal sample for analysis obtained above, the X-ray source is monochromatic AlKα, the X-ray beam diameter is 100 μmφ (25 W, 15 kV), the pass energy is narrow scan: 58.70 eV, and the charge is neutralized. The number was measured by 10 narrow scans, and the energy step was measured by narrow scan: 0.25 eV. Before the XPS measurement, the surface of the sample was sputtered for 1 minute at an acceleration voltage of 1.0 kV over an area of 2 mm×2 mm to clean it. According to the XPS measurement results, the obtained oxidized coal had a carboxyl group content of 16.7 atm % and an epoxy group content of 6.3 atm %. The measurement results are shown in FIG.

<<Production example of graphene oxide (GO)>>
A graphene oxide dispersion was prepared in the same manner as above, except that graphene powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of anthracite. The obtained sample was heat-treated in a baking machine for 1 hour to prepare a sample for analysis. When XPS of graphene oxide was measured in the same manner as above, the carboxyl group content was 5.1 atm % and the epoxy group content was 46.9 atm %. FIG. 3 shows the XPS measurement results.

<<Production example of positive electrode precursor and electrolytic solution>>
[Preparation of positive electrode active material]
The crushed coconut shell charcoal was placed in a small carbonization furnace and carbonized at 500° C. for 3 hours in a nitrogen atmosphere to obtain a charcoal. The obtained carbide was placed in an activation furnace, 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 activated carbon was taken out and cooled in a nitrogen atmosphere to obtain activated carbon. The activated carbon obtained was washed with water for 10 hours, drained, dried in an electric dryer maintained at 115° C. for 10 hours, and then pulverized in a ball mill for 1 hour to obtain activated carbon 1. The average particle size of Activated Carbon 1 was measured using a laser diffraction particle size distribution analyzer (SALD-2000J) manufactured by Shimadzu Corporation and found to be 5.5 μm. In addition, the pore distribution of activated carbon 1 was measured using a pore distribution analyzer (AUTOSORB-1 AS-1-MP) manufactured by Yuasa Ionics. As a result, the BET specific surface area was 2360 m ² /g, the mesopore volume (V ₁ ) was 0.52 cm ³ /g, the micropore volume (V ₂ ) was 0.88 cm ³ /g, and V ₁ /V ₂ =0. was 59.

[Production of positive electrode precursor 1]
55.4% by weight of activated carbon 1, 1.5% by weight of CMC (carboxymethylcellulose), 31.1% by weight of lithium carbonate, 2.4% by weight of carbon black (CB), and 3% by weight of acrylic latex (LTX) 9% by mass, 1.8% by mass of PVP (polyvinylpyrrolidone), and distilled water so that the mass ratio of the solid content is 15.0% by mass. Tori Mixer (registered trademark)" was used to disperse for 20 minutes at a rotational speed of 2000 rpm to obtain a mixture. The obtained mixture was mixed with an oxidized coal dispersion so that the solid content of the oxidized coal was 3.9% by mass, and dispersed 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 resulting coating liquid were measured using an E-type viscometer TVE-35H manufactured by Toki Sangyo Co., Ltd. As a result, the viscosity (ηb) was 520 mPa·s and the TI value was 2.4. Using a doctor blade, one side of an aluminum foil having a thickness of 15 μm was coated with the positive electrode coating solution 1, dried on a hot plate heated to 50° C. for 10 minutes, and then pressed using a roll press at a pressure of 6 kN/cm. A positive electrode precursor 1 was obtained by pressing under the condition that the surface temperature of the pressed part was 25°C.

[Analysis of positive electrode precursor]
The surface of the positive electrode active material layer of the positive electrode precursor 1 was coated with a gold film having a thickness of several nm by sputtering gold in a vacuum of 10 Pa. Subsequently, under the conditions shown below, an SEM image of the surface of the positive electrode active material layer was taken under atmospheric exposure.
(SEM measurement conditions)
・ Measuring device: Field emission scanning electron microscope S-4700 manufactured by Hitachi High-Technologies Co., Ltd.
・Acceleration voltage: 1 kV
・Emission current: 10 μA
・Measuring magnification: 5,000 times ・Detector: Secondary electron detector ・Electron beam incident angle: 90°
In photographing, the brightness and contrast were adjusted so that there were no pixels reaching the maximum brightness value in the SEM image and the average brightness value was within the range of 40% to 60% of the maximum brightness value.

[Production Examples of Positive Electrode Precursors 2 to 10]
Positive electrode precursors 2 to 6 were produced in the same manner as [Production of positive electrode precursor 1] except that the amount of each component used was adjusted as shown in Table 1.

FIG. 4 is an SEM image of the positive electrode precursor 1 taken at a magnification of 5,000. It was confirmed that the positive electrode active material (activated carbon 1) and the alkali metal compound (lithium carbonate) were uniformly coated with coal oxide. FIG. 5 is an SEM image of the positive electrode precursor 5 taken at a magnification of 5,000. It was confirmed that there was no deposit on the positive electrode active material and on the alkali metal compound. FIG. 6 is an SEM image of the positive electrode precursor 6 taken at a magnification of 5,000. It was confirmed that the positive electrode active material and the alkali metal compound were uniformly covered with graphene oxide, but the gaps in the positive electrode active material layer were also covered because the sheet size of the graphene oxide was large.

[Preparation of electrolyte solution 1]
As an organic solvent, a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 33:67 (volume ratio) was used, and the concentration ratio of _LiPF6 and LiFSI was 1:1, for a total of 1.2 mol/ A non-aqueous electrolytic solution 1 was obtained by dissolving the electrolytic salt so as to have a concentration of L.

<<Example 1>>
<Manufacturing of monopolar cells>
One piece of the obtained positive electrode precursor 1 was cut out so that the positive electrode active material layer had a size of 4.4 cm×9.4 cm, and vacuum-dried at a temperature of 150° C. for 12 hours to obtain a working electrode. Subsequently, a piece of copper foil having a thickness of 10 μm was cut into a size of 4.5 cm×9.5 cm, and a metallic lithium foil having a thickness of 50 μm and a size of 4.4 cm×9.4 cm was attached to the copper foil as a counter electrode. . One sheet of 4.7 cm×9.8 cm polyethylene separator (manufactured by Asahi Kasei Corporation, thickness 15 μm) and a 4.7 cm×9.8 cm glass filter were prepared. Using these, a working electrode (positive electrode precursor 1), a separator, a glass filter, and a counter electrode (metallic lithium electrode) are laminated in this order so that the positive electrode active material layer and the metallic lithium foil face each other with the separator and glass filter interposed therebetween. to obtain an electrode laminate. A positive electrode terminal and a negative electrode terminal were ultrasonically welded to the obtained electrode body, placed in an exterior body formed of an aluminum laminate packaging material, and three sides including the electrode terminal portion were heat-sealed.

[Injection, impregnation, sealing process]
About 5.0 g of the non-aqueous electrolytic solution 1 was poured into the outer package housing the electrode laminate under atmospheric pressure, in a dry air environment with a temperature of 25° C. and a dew point of −40° C. or lower. Subsequently, the outer package housing the electrode laminate and the non-aqueous electrolytic solution was placed in a decompression chamber, and the pressure was reduced from the atmospheric pressure to −87 kPa, then returned to the atmospheric pressure, and allowed to stand for 5 minutes. After that, the exterior body in the chamber was evacuated from the atmospheric pressure to -87 kPa, and after repeating the step of returning to the atmospheric pressure four times, the chamber was allowed to stand under the atmospheric pressure for 15 minutes. The electrode laminate was impregnated with the non-aqueous electrolytic solution 1 through the above steps. After that, the electrode laminate impregnated with the non-aqueous electrolytic solution 1 is placed in a vacuum sealing machine, and the exterior body is sealed by sealing at 180 ° C. for 10 seconds at a pressure of 0.1 MPa while reducing the pressure to -95 kPa. Then, a monopolar cell was produced.

<Evaluation of monopolar cell>
[Capacitance measurement]
The capacitance Qa (mAh/g) is a value obtained by the following method. First, in a constant temperature bath set at 25 ° C., the monopolar cell was subjected to constant current charging at a current value of 3 C until reaching 4.0 V, and then constant voltage charging to apply a constant voltage of 4.0 V in total. Allow 30 minutes. Subsequently, the electric capacity (mAh) is obtained when the sampling interval is set to 1.0 second and the constant current discharge is performed at a current value of 1C to 2.0V. A value calculated by dividing the obtained electric capacity by the weight of the positive electrode active material is defined as the electric capacity Qa (mAh/g). The weight of the positive electrode active material is calculated by subtracting the weight of the aluminum foil from the weight of the positive electrode precursor to calculate the weight of the positive electrode active material layer, and multiplying it by the composition ratio (% by mass) of the positive electrode active material shown in Table 1. be able to.

[Measurement of decomposition capacity of alkali metal compound]
The decomposition capacities Qb (mAh) and Qc (mAh/g) of alkali metal compounds are values obtained by the following method. First, the monopolar cell was subjected to constant current charging at a current value of 3 C in a constant temperature bath set at 45 ° C. until reaching 4.5 V, followed by constant voltage charging to apply a constant voltage of 4.5 V in total. After 3 hours, the decomposition capacity Qb (mAh) is obtained as the electric capacity that flows at a voltage of 4.2 V or higher. A decomposition capacity Qc (mAh/g) is obtained by dividing the obtained electric capacity Qb by the weight of the alkali metal compound. The weight of the alkali metal compound is calculated by subtracting the weight of the aluminum foil from the weight of the positive electrode precursor to calculate the weight of the positive electrode active material layer, and multiplying the result by the composition ratio (% by mass) of the alkali metal compound shown in Table 1. be able to. Here, when lithium carbonate is used as the alkali metal compound, the decomposition efficiency of lithium carbonate can be calculated by dividing Qc by the theoretical capacity of 725 mAh/g for decomposition of lithium carbonate.

[Examples 2 to 8, Comparative Examples 1 and 2]
A monopolar cell was produced in the same manner as in Example 1, except that the positive electrode precursor was used as shown in Table 2.

When the content A of the oxidized coal was 0.5% by mass or more and 8.0% by mass or less, the electrostatic capacity Qa could be increased, and the decomposition capacity and decomposition efficiency of the alkali metal compound could be increased. When graphene oxide is used instead of oxidized coal, the surface of the positive electrode active material layer is excessively covered, so that the liquid retention and diffusibility of the electrolyte are reduced, and the decomposition capacity and decomposition efficiency of the alkali metal compound are reduced. It is thought that In addition, it is thought that the graphene oxide was reduced by drying in a high temperature environment of 150 ° C. and the functional group disappeared, so that the capacitance did not increase and the decomposition capacity and decomposition efficiency of the alkali metal compound decreased. be done.

The positive electrode precursor of the present disclosure is preferable because the effect of the present invention is maximized when applied as a lithium ion capacitor, and a power regeneration system for a hybrid drive system of an automobile that requires high energy density, solar power generation. and natural power generation such as wind power generation, power load leveling systems in micro grids, etc., uninterruptible power supply systems in factory production equipment, leveling of voltage fluctuations such as microwave power transmission and electrolytic resonance, and energy storage It can be suitably used as a non-aqueous alkali metal storage element used in a non-contact power feeding system, an energy harvesting system for the purpose of utilizing power generated by vibration power generation, or the like. A lithium-ion capacitor can be made into an electric storage module by connecting, for example, a plurality of non-aqueous alkali metal electric storage elements in series or in parallel.

Claims (4)

A positive electrode precursor comprising a positive electrode active material containing a carbon material, coal oxide, and an alkali metal compound other than the positive electrode active material,
The positive electrode precursor has a positive electrode current collector and a positive electrode active material layer containing the positive electrode active material and the coal oxide provided on one or both sides of the positive electrode current collector,
A positive electrode precursor, wherein at least part of the surface of the positive electrode active material and at least part of the surface of the alkali metal compound are coated with the coal oxide. The content of the coal oxide contained in the positive electrode active material layer of the positive electrode precursor is 0.5% by mass or more and 8.0% by mass or less based on the total mass of the positive electrode active material layer, and the alkali metal The positive electrode precursor according to claim 1, wherein the content of the compound is 20.0% by mass or more and 45.0% by mass or less based on the total mass of the positive electrode active material layer. The carboxyl group functional group amount measured by XPS (X-ray photoelectron spectroscopy) of the oxidized coal is 10.0 atm% or more and 26.0 atm% or less, and the epoxy group functional group amount is 0.1 atm% or more and 8.0 atm%. 3. The positive electrode precursor according to claim 1 or 2, wherein: The positive electrode precursor according to any one of claims 1 to 3, wherein the sheet size of the oxidized coal measured by AFM (atomic force microscope) is 10 nm or more and less than 50 nm.

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