Positive electrode precursor and positive electrode slurry

Abstract

To provide a positive electrode precursor for a non-water system hybrid capacitor with excellent high-output and input and high temperature durability, capable of attaining reduction in both process time and defective rate during manufacturing, and to provide a slurry that enables the manufacturing of the same.SOLUTION: After the addition of a sodium hydroxide solution to a positive electrode active material layer fetched after immersing a positive electrode precursor in water for 24 hours, the whole acid functional group content of the positive electrode active material layer calculated by back titration using hydrochloric acid is 0.15 mmol / g or more and 2.00 mmol / g or less, based on the weight of the positive electrode active material layer, and / or after a slurry of pH 9.0 or more containing a positive electrode active material, another alkali metal chemical compound, a biding agent, a water-soluble polymer, and a solvent is dried in order to remove the solvent, and the sodium hydroxide solution is added to a solid material fetched after immersion in water for 24 hours, the whole acid functional group content of the solid material calculated by back titration using hydrochloric acid is 0.15 mmol / g or more and 2.00 mmol / g or less, based on the weight of the solid material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a positive electrode precursor and a slurry for the production of a positive electrode for a non-aqueous hybrid capacitor. [Background technology]

[0002] In recent years, from the perspective of protecting the global environment and effectively utilizing energy to conserve resources, attention has been drawn to wind power generation power smoothing systems or late-night power storage systems, distributed home energy storage systems based on solar power generation technology, and energy storage systems for electric vehicles.

[0003] The primary requirement for batteries used in these energy storage systems is a high energy density, and the development of lithium-ion batteries is being actively pursued as a promising candidate for a high-energy-density battery that can meet this requirement.

[0004] The second requirement is high output characteristics. For example, in a combination of a high-efficiency engine and a power storage system (e.g., a hybrid electric vehicle) or a combination of a fuel cell and a power storage system (e.g., a fuel cell electric vehicle), the power storage system is required to have high output discharge characteristics during acceleration.

[0005] Currently, electric double layer capacitors, nickel-metal hydride batteries, and the like are being developed as high-power storage devices.

[0006] Among electric double layer capacitors, those that use activated carbon for the electrodes have output characteristics of approximately 0.5 to 1 kW / L. These electric double layer capacitors also have high durability (cycle characteristics and high-temperature storage characteristics), and have been considered the optimal device for the above-mentioned fields that require high output. However, their energy density is only approximately 1 to 5 Wh / L. Therefore, further improvement in energy density is necessary.

[0007] On the other hand, nickel-metal hydride batteries currently used in hybrid electric vehicles have high output equivalent to that of electric double-layer capacitors and an energy density of about 160 Wh / L. However, vigorous research is being conducted to further increase their energy density and output, as well as to improve their durability.

[0008] Research is also underway to increase the output of lithium-ion batteries. For example, lithium-ion batteries have been developed that can achieve high output of over 3 kW / L at a discharge depth of 50% (a value indicating the percentage of the discharge capacity of the storage element that has been discharged). However, their energy density is below 100 Wh / L, a design that deliberately suppresses the high energy density that is the greatest feature of lithium-ion batteries. Their durability (cycle characteristics and high-temperature storage characteristics) is inferior to that of electric double-layer capacitors. Therefore, to ensure practical durability, they must be used within a discharge depth range narrower than 0 to 100%. Because the actual usable capacity is even smaller, vigorous research is being conducted to further improve the durability of lithium-ion batteries.

[0009] As described above, there is a strong demand for practical application of energy storage devices that combine high energy density, high output characteristics, and durability. However, the existing energy storage devices described above each have their own advantages and disadvantages. Therefore, new energy storage devices that satisfy these technical requirements are needed. As a promising candidate, an energy storage device called a lithium-ion capacitor has attracted attention and is being actively developed.

[0010] The energy of the capacitor is 1 / 2 C V 2 where C is the capacitance and V is the voltage.

[0011] A lithium-ion capacitor is a type of energy storage element (non-aqueous hybrid capacitor) that uses a non-aqueous electrolyte containing lithium salt. At the positive electrode, charging and discharging takes place at approximately 3 V or higher through a non-Faradaic reaction caused by the adsorption and desorption of anions, similar to an electric double-layer capacitor; and at the negative electrode, charging and discharging takes place through a Faradic reaction caused by the absorption and release of lithium ions, similar to a lithium-ion battery.

[0012] To summarize the above-mentioned electrode materials and their characteristics, when materials such as activated carbon are used for the electrodes and charging and discharging is performed by the adsorption and desorption of ions on the surface of the activated carbon (non-Faradaic reaction), high output and durability are achieved, but the energy density is low (for example, 1x).When oxides or carbon materials are used for the electrodes and charging and discharging is performed by the Faraday reaction, the energy density is high (for example, 10x that of non-Faraday reactions using activated carbon), but there are issues with durability and output characteristics.

[0013] As a combination of these electrode materials, electric double layer capacitors use activated carbon (energy density 1x) for the positive and negative electrodes, and are characterized by charging and discharging through non-Faradic reactions at both the positive and negative electrodes.They have high output and high durability, but are characterized by low energy density (positive electrode 1x x negative electrode 1x = 1).

[0014] Lithium-ion secondary batteries use lithium transition metal oxides (10 times the energy density) for the positive electrode and carbon materials (10 times the energy density) for the negative electrode, and are characterized by charging and discharging through the Faraday reaction at both the positive and negative electrodes, resulting in a high energy density (10 times the positive electrode x 10 times the negative electrode = 100), but they have issues with output characteristics and durability. In order to satisfy the high durability required for hybrid electric vehicles and the like, the depth of discharge must be limited, and with lithium-ion secondary batteries, only 10 to 50% of the energy can be used.

[0015] Lithium-ion capacitors are a new asymmetric capacitor that combines the features of electric double-layer capacitors and lithium-ion secondary batteries. They use activated carbon (energy density 1x) for the positive electrode and carbon material (energy density 10x) for the negative electrode, and are characterized by charging and discharging through a non-Faradic reaction at the positive electrode and a Faradic reaction at the negative electrode. Lithium-ion capacitors are characterized by high output and durability, as well as a high energy density (positive electrode 1x x negative electrode 10x = 10), and do not require limitations on the depth of discharge like lithium-ion secondary batteries.

[0016] Various studies have been conducted on the above-described power storage elements (particularly lithium ion capacitors and lithium ion secondary batteries). For example, Patent Document 1 discloses a positive electrode precursor for a high-capacity non-aqueous hybrid capacitor, which promotes the decomposition of an alkali metal compound contained in the positive electrode precursor and enables pre-doping of the negative electrode in a short period of time. Patent Document 2 discloses a positive electrode coating liquid for a positive electrode precursor and a positive electrode precursor that can not only promote the decomposition of alkali metal compounds but also suppress the loss of positive electrode active material during pre-doping and have high temperature durability at 85°C or higher. Patent Document 3 proposes a non-aqueous lithium energy storage element that has both high-temperature durability and input performance, and discloses a positive electrode that contains activated carbon with a specific average particle size and amount of functional groups as a positive electrode active material. Patent Document 4 discloses an electrode for a lithium ion battery having an electrode resistance within a specific range in order to realize a lithium ion battery that is excellent in both battery characteristics and safety. Patent Document 5 discloses a positive electrode slurry for a non-aqueous hybrid capacitor that enables uniform decomposition of alkali metal carbonate, has high energy density and high input / output, and is also excellent in high-temperature durability. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] International Publication No. 2017 / 126687 [Patent Document 2] International Publication No. 2019 / 156090 [Patent Document 3] International Publication No. 2021 / 066174 [Patent Document 4] International Publication No. 2018 / 016528 [Patent Document 5] Japanese Patent Application Publication No. 2019-29420 Summary of the Invention [Problem to be solved by the invention]

[0018] The methods described in Patent Documents 1 to 5 take into consideration the prevention of loss of the positive electrode active material due to gas generation in the pre-doping step and the resulting micro-short circuit, as well as the state of the positive electrode active material itself and the state of the positive electrode slurry and / or positive electrode active material layer. However, the methods for obtaining a positive electrode or positive electrode precursor described in Patent Documents 1 to 5 do not sufficiently consider the state of the carbon material, which is the positive electrode active material in the presence of the alkali metal compound in the positive electrode slurry or positive electrode active material layer, and there is room for further improvement in shortening the process time and reducing the defect rate during the production of a nonaqueous hybrid capacitor, as well as in reducing the resistance and improving the durability of the nonaqueous hybrid capacitor.

[0019] Therefore, an object of the present invention is to provide a positive electrode precursor and a positive electrode slurry for a non-aqueous hybrid capacitor that can shorten the manufacturing process time and reduce the defect rate, and that has high input / output and excellent high-temperature durability. [Means for solving the problem]

[0020] The present inventors conducted extensive research and experiments to solve the above-mentioned problems. As a result, the present inventors discovered that by adding carboxymethyl cellulose to a positive electrode precursor and positive electrode slurry for a non-aqueous hybrid capacitor containing a carbon material and an alkali metal compound, and controlling the total amount of acidic functional groups to a specific level as an indicator of the state of carboxymethyl cellulose adsorption on the surface of the carbon material (positive electrode active material), and controlling the positive electrode precursor to have a specific mixed solvent impregnation property, electrode resistance, and peel strength, or by controlling the positive electrode slurry to have a specific alkalinity and slurry viscosity, the carbon material and alkali metal compound can be uniformly distributed in the positive electrode precursor without localization, and the carbon material surface can maintain electrolyte retention while suppressing the formation of a coating due to a side reaction, thereby enabling smooth ion adsorption and desorption. When the positive electrode precursor is incorporated into a non-aqueous hybrid capacitor, the electrolyte impregnation time can be shortened, the electrode strength can be maintained, and the defect rate can be reduced, and high input / output and high-temperature durability can be excellent. Based on these findings, the present invention has been completed. Specifically, the present invention is as follows. [1] A positive electrode precursor having a positive electrode current collector and a positive electrode active material layer on one or both surfaces of the positive electrode current collector, the positive electrode active material layer containing a positive electrode active material, an alkali metal compound other than the positive electrode active material, a binder, and a water-soluble polymer; the positive electrode active material is a carbon material, the carbon material includes activated carbon, and the water-soluble polymer includes carboxymethyl cellulose; the positive electrode precursor is immersed in water for 24 hours, and then the positive electrode active material layer is taken out. A sodium hydroxide solution is added to the positive electrode active material layer, and the total amount of acidic functional groups in the positive electrode active material layer is calculated by back titration using hydrochloric acid, and the total amount of acidic functional groups in the positive electrode active material layer is 0.15 mmol / g or more and 2.00 mmol / g or less by weight of the positive electrode active material layer, the penetration time when 3 μL of a mixed solvent of ethylene carbonate: methyl ethyl carbonate = 33:67 (volume ratio) is dropped onto the positive electrode precursor is 5 seconds or more and 40 seconds or less, The volume resistivity of the positive electrode active material layer of the positive electrode precursor is 1.0 Ω cm or more and 10.0 Ω cm or less, and the interface resistance between the positive electrode active material layer and the positive electrode current collector is 0.01 Ω cm2 Above 1.00 Ω·cm 2 Is below, and A positive electrode precursor in which the peeling strength of the positive electrode active material layer is 0.02 N / cm or more and 3.00 N / cm or less. [2] The positive electrode precursor according to item 1, wherein the ratio of the water-soluble polymer to the total mass of the carbon material contained in the positive electrode active material layer is 0.5% by mass or more and 10.0% by mass or less. [3] The positive electrode precursor according to item 1 or 2, wherein the alkali metal compound is at least one selected from the group consisting of lithium carbonate, sodium carbonate, and potassium carbonate. [4] The positive electrode precursor according to any one of items 1 to 3, wherein the alkali metal compound is lithium carbonate. [5] In the positive electrode active material layer, the alkali metal compound is 10% by mass or more and 50% by mass or less Contained, the positive electrode precursor according to any one of items 1 to 4. [6] The binder has oxidation resistance of 4.3 V (vs. Li / Li + ) or more, the positive electrode precursor according to any one of items 1 to 5. [7] The positive electrode precursor according to any one of items 1 to 6, wherein the binder is an acrylic latex. [8] When the mesopore volume derived from pores having a diameter of 20 Å or more and 500 Å or less calculated by the BJH method is V1 (cm 3 / g), and the micropore volume derived from pores having a diameter of less than 20 Å calculated by the MP method is V2 (cm 3 / g), the activated carbon satisfies 0.3 < V1 ≤ 0.8 and 0.5 ≤ V2 ≤ 1.0, and the specific surface area measured by the BET method is 1,500 m 2 / g or more and 3,000 m 2 / g or less, the positive electrode precursor according to any one of items 1 to 7. [9] The activated carbon has a mesopore volume V1 (cm derived from pores having a diameter of 20 Å or more and 500 Å or less calculated by the BJH method3 / g) satisfies 0.8 < V1 ≤ 2.5, and the micropore volume V2 (cm 3 / g) derived from pores with a diameter of less than 20 Å calculated by the MP method satisfies 0.8 < V2 ≤ 3.0, and the specific surface area measured by the BET method is 2,300 m 2 / g or more and 4,000 m 2 / g or less, the cathode precursor according to any one of items 1 to 7. 〔10〕 When the average particle diameter of the above alkali metal compound is X1, 0.1 μm ≤ X1 ≤ 10 μm, and when the average particle diameter of the above cathode active material is Y1, 2 μm ≤ Y1 ≤ 20 μm, and X1 < Y1, the cathode precursor according to any one of items 1 to 9. 〔11〕 For the production of the cathode of a non-aqueous hybrid capacitor, the cathode precursor according to any one of items 1 to 10. 〔12〕 A slurry containing a cathode active material, an alkali metal compound other than the above cathode active material, a binder, a water-soluble polymer, and a solvent, The above cathode active material is a carbon material, the above carbon material contains activated carbon, the above water-soluble polymer contains carboxymethyl cellulose, The above slurry is alkaline with a pH of 9.0 or more, The shear rate of the above slurry is 5 s -1 、50 s -1 、500 s -1 、and 2000 s -1 When the viscosities at and are η1 (mPa·s), η2 (mPa·s), η3 (mPa·s), and η4 (mPa·s) respectively, 0.10 ≤ η2 / η1 ≤ 1.00, and 0.10 ≤ η3 / η2 ≤ 1.00, and 0.10 ≤ η4 / η3 ≤ 1.00, After drying the above slurry to remove the solvent, after adding a sodium hydroxide solution to the solid taken out after immersing in water for 24 hours, the total acidic functional group amount of the above solid calculated by back titration using hydrochloric acid is 0.15 mmol / g or more and 2.00 mmol / g or less per unit weight of the solid. 〔13〕 The slurry according to item 12, wherein the ratio of the water-soluble polymer to the total mass of the carbon material contained in the slurry is 0.5% by mass or more and 10.0% by mass or less. 〔14〕 The slurry according to item 12 or 13, wherein the alkali metal compound is at least one selected from the group consisting of lithium carbonate, sodium carbonate, and potassium carbonate. 〔15〕 The slurry according to any one of items 12 to 14, wherein the alkali metal compound is lithium carbonate. 〔16〕 The slurry according to any one of items 12 to 15, wherein in the slurry, the ratio of the alkali metal compound to the total mass of all solids excluding the solvent is 10% by mass or more and 50% by mass or less. 〔17〕 The slurry according to any one of items 12 to 16, wherein the binder has oxidation resistance of 4.3 V (vs. Li / Li+) or more. 〔18〕 The slurry according to any one of items 12 to 17, wherein the binder is acrylic latex. 〔19〕 When 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 for the activated carbon is V1 (cm 3 / g), and the amount of micropores derived from pores with a diameter of less than 20 Å calculated by the MP method is V2 (cm 3 / g), the slurry according to any one of items 12 to 18 satisfies 0.3 < V1 ≤ 0.8 and 0.5 ≤ V2 ≤ 1.0, and the specific surface area measured by the BET method is 1,500 m 2 / g or more and 3,000 m 2 / g or less. 〔20〕 When the amount of mesopores V1 (cm 3 / g) derived from pores with a diameter of 20 Å or more and 500 Å or less calculated by the BJH method for the activated carbon satisfies 0.8 < V1 ≤ 2.5, and the amount of micropores V2 (cm 3 / g) derived from pores with a diameter of less than 20 Å calculated by the MP method satisfies 0.8 < V2 ≤ 3.0, and the specific surface area measured by the BET method is 2,300 m2 4,000 m or more per g 2 The slurry according to any one of items 12 to 18, which is per g or less. 〔21〕 The slurry according to any one of items 12 to 20, wherein when the average particle diameter of the alkali metal compound is X1, 0.1 μm ≤ X1 ≤ 10 μm, when the average particle diameter of the positive electrode active material is Y1, 2 μm ≤ Y1 ≤ 20 μm, and X1 < Y1. 〔22〕 The slurry according to any one of items 12 to 21, which is for producing a positive electrode of a non-aqueous hybrid capacitor.

Advantages of the Invention

[0021] According to the present invention, it is possible to shorten the process time and reduce the defect rate during the production of a non-aqueous hybrid capacitor, and to provide a positive electrode precursor for a non-aqueous hybrid capacitor having high input / output and excellent high-temperature durability, and a slurry capable of producing the same.

Mode for Carrying Out the Invention

[0022] Hereinafter, embodiments of the present invention (hereinafter referred to as "the present embodiments") will be described in detail, but the present invention is not limited to the present embodiments. The upper limit value and the lower limit value in each numerical range of the present embodiments can be arbitrarily combined to form an arbitrary numerical range.

[0023] 《Non-aqueous Hybrid Capacitor》 A non-aqueous hybrid capacitor generally has a positive electrode, a negative electrode, a separator, and an electrolytic solution as main components. As the electrolytic solution, an organic solvent (hereinafter referred to as "non-aqueous electrolytic solution") in which an electrolyte such as an alkali metal salt is dissolved is used.

[0024] In this specification, the state of the positive electrode before pre-doping is defined as "positive electrode precursor", and the state of the positive electrode after pre-doping is defined as "positive electrode". In this specification, a slurry for producing a positive electrode precursor or a positive electrode is referred to as a "positive electrode slurry".

[0025] <Positive electrode precursor> The positive electrode precursor of the present invention has a positive electrode current collector and a positive electrode active material layer on one or both sides of the positive electrode current collector, the positive electrode active material layer containing a positive electrode active material, an alkali metal compound other than the positive electrode active material, a binder, and a water-soluble polymer, the positive electrode active material being a carbon material, the carbon material containing activated carbon, and the water-soluble polymer containing carboxymethyl cellulose, the positive electrode precursor being immersed in water for 24 hours, and then removed from the positive electrode active material layer, and a sodium hydroxide solution is added to the positive electrode active material layer, and the positive electrode precursor is subjected to back titration using hydrochloric acid to obtain a positive electrode active material layer. The calculated total amount of acidic functional groups in the positive electrode active material layer is 0.15 mmol / g or more and 2.00 mmol / g or less per weight of the positive electrode active material layer, the penetration time when 3 μL of a mixed solvent of ethylene carbonate:methyl ethyl carbonate=33:67 (volume ratio) is dropped onto the positive electrode precursor is 5 seconds or more and 40 seconds or less, the volume resistivity of the positive electrode active material layer of the positive electrode precursor is 1.0 Ω cm or more and 10.0 Ω cm or less, and the interfacial resistance between the positive electrode active material layer and the positive electrode current collector is 0.01 Ω cm 2 More than 1.00Ω cm 2 The positive electrode precursor according to the present embodiment may be simply referred to as an electrode before pre-doping, a one-side electrode before pre-doping, a half-cell, a coated electrode, a dried electrode, or the like, depending on the desired configuration of the nonaqueous hybrid capacitor.

[0026] [Cathode active material layer] The positive electrode active material layer contained in the positive electrode precursor of this embodiment contains an alkali metal compound other than the positive electrode active material. In this embodiment, when assembling the energy storage device, it is preferable to pre-dope the negative electrode with alkali metal ions. As a pre-doping method, it is preferable to assemble the energy storage device using a positive electrode precursor containing the alkali metal compound, a negative electrode, a separator, and a non-aqueous electrolyte solution, and then apply a voltage between the positive electrode precursor and the negative electrode.

[0027] The positive electrode active material layer contained in the positive electrode precursor contains a positive electrode active material composed of a carbon material containing activated carbon, an alkali metal compound other than the above positive electrode active material, a water-soluble polymer containing carboxymethyl cellulose, and a binder. The positive electrode active material layer may contain optional components such as a conductive filler as required in addition to the above.

[0028] -Positive electrode active material- The above positive electrode active material is a carbon material. The carbon material includes activated carbon. As the positive electrode active material, one kind of carbon material may be used alone, or two or more kinds of carbon materials may be mixed and used, and it may contain materials other than carbon materials (such as composite oxides of alkali metals and transition metals, etc.). Examples of carbon materials other than activated carbon include carbon nanotubes, conductive polymers, and porous carbon materials.

[0029] The content rate of the carbon material with respect to the total mass of the positive electrode active material is preferably 50% by mass or more, more preferably 70% by mass or more, or may be 100% by mass. From the viewpoint of obtaining good effects by using in combination with other materials, for example, the content rate of the carbon material is preferably 90% by mass or less, or may be 80% by mass or less with respect to the total mass of the positive electrode active material.

[0030] Activated carbon is used as the positive electrode active material, but the type of activated carbon and its raw material are not particularly limited. However, in order to achieve both high input / output characteristics and high energy density, it is preferable to optimally control the pores of the activated carbon. Specifically, when the mesopore volume derived from pores with a diameter of 20 Å or more and 500 Å or less calculated by the BJH method is V1 (cm 3 / g), and the micropore volume derived from pores with a diameter of less than 20 Å calculated by the MP method is V2 (cm 3 / g), (1) In order to obtain high input / output characteristics, activated carbon (hereinafter also referred to as "activated carbon 1") that satisfies 0.3 < V1 ≤ 0.8, and 0.5 ≤ V2 ≤ 1.0, and has a specific surface area measured by the BET method of 1,500 m 2 / g or more and 3,000 m 2 / g or less is preferable, and (2) To obtain a high energy density, it is necessary to satisfy 0.8 < V1 ≤ 2.5 and 0.8 < V2 ≤ 3.0, and the specific surface area measured by the BET method is 2,300 m 2 / g or more and 4,000 m 2 / g or less of activated carbon (hereinafter also referred to as "activated carbon 2") is preferred.

[0031] Hereinafter, the above (1) activated carbon 1 and the above (2) activated carbon 2 will be sequentially described individually.

[0032] (Activated carbon 1) The mesopore volume V1 of activated carbon 1 is preferably greater than 0.3 cm 3 / g in terms of increasing the input / output characteristics when incorporated into the energy storage element. On the other hand, from the point of suppressing the decrease in the bulk density of the positive electrode, it is preferably 0.8 cm 3 / g or less. The above V1 is more preferably 0.35 cm 3 / g or more and 0.7 cm 3 / g or less, and even more preferably 0.4 cm 3 / g or more and 0.6 cm 3 / g or less.

[0033] The micropore volume V2 of 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 the capacity. On the other hand, from the point of suppressing the bulk of the activated carbon, increasing the density as an electrode, and increasing the capacity per unit volume, it is preferably 1.0 cm 3 / g or less. The above V2 is more preferably 0.6 cm 3 / g or more and 1.0 cm 3 / g or less, and even more preferably 0.8 cm 3 / g or more and 1.0 cm 3 / g or less.

[0034] The ratio of mesopore volume V1 to micropore volume V2 of activated carbon 1 (V1 / V2) is preferably in the range of 0.3≦V1 / V2≦0.9. That is, from the viewpoint of increasing the ratio of mesopore volume to micropore volume to an extent that can suppress a decrease in capacity while maintaining high input / output characteristics, V1 / V2 is preferably 0.3 or more. On the other hand, from the viewpoint of increasing the ratio of micropore volume to mesopore volume to an extent that can suppress a decrease in capacity while maintaining high input / output characteristics, V1 / V2 is preferably 0.9 or less, more preferably 0.4≦V1 / V2≦0.7, and even more preferably 0.55≦V1 / V2≦0.7.

[0035] For V1, V2, and V1 / V2 of activated carbon 1, the upper and lower limits of the preferred ranges described above can be combined in any desired manner.

[0036] The average pore diameter of the activated carbon 1 is set to 17 Å or more (i.e., 17×10 -10 In order to increase the capacity, the average pore diameter of the activated carbon 1 is preferably 25 Å or less.

[0037] The BET specific surface area of ​​activated carbon 1 is 1,500 m 2 / g or more 3,000m 2 / g or less, and 1,500m 2 / g or more 2,500m 2 / g or less is more preferable. 2 / g or more, a good energy density is easily obtained, while a BET specific surface area of ​​3,000 m 2 When the BET specific surface area is 0.01g or less, it is not necessary to add a large amount of binder to maintain the strength of the electrode, and therefore the performance per electrode volume is improved. The upper and lower limits of the above range of the BET specific surface area can be combined arbitrarily.

[0038] The activated carbon 1 having the above-mentioned characteristics can be obtained, for example, using the raw materials and processing method described below.

[0039] In this embodiment, the carbon source used as the raw material for the activated carbon 1 is not particularly limited. Examples include plant-based raw materials such as wood, wood flour, coconut shells, pulp manufacturing by-products, bagasse, and blackstrap molasses; fossil-based raw materials such as peat, lignite, brown coal, bituminous coal, anthracite, petroleum distillation residue components, petroleum pitch, coke, and coal tar; various synthetic resins such as phenolic resins, vinyl chloride resins, vinyl acetate resins, melamine resins, urea resins, resorcinol resins, celluloid, epoxy resins, polyurethane resins, polyester resins, and polyamide resins; synthetic rubbers such as polybutylene, polybutadiene, and polychloroprene; other synthetic woods, synthetic pulps, and carbonized versions of these. Among these raw materials, plant-based raw materials such as coconut shells and wood flour, and carbonized versions of these, are preferred from the standpoints of mass production and cost, with coconut shell carbonized versions being particularly preferred.

[0040] As a carbonization and activation method for obtaining the activated carbon 1 from these raw materials, known methods such as a fixed bed method, a moving bed method, a fluidized bed method, a slurry method, a rotary kiln method, etc. can be used.

[0041] Examples of methods for carbonizing these raw materials include a method of firing them using an inert gas such as nitrogen, carbon dioxide, helium, argon, xenon, neon, carbon monoxide, or combustion exhaust gas, or a mixed gas containing these inert gases as the main component with other gases, at 400 to 700°C, preferably 450 to 600°C, for about 30 minutes to 10 hours.

[0042] As a method for activating the carbonized material obtained by the above carbonization method, a gas activation method is preferably used in which the carbonized material is fired using an activation gas such as water vapor, carbon dioxide, oxygen, etc. Among these, a method using water vapor or carbon dioxide as the activation gas is preferred.

[0043] In this activation method, it is preferable to activate the carbonized material by raising the temperature to 800 to 1,000°C over a period of preferably 3 to 12 hours, more preferably 5 to 11 hours, and even more preferably 6 to 10 hours, while supplying the activation gas at a rate of preferably 0.5 to 3.0 kg / h, more preferably 0.7 to 2.0 kg / h.

[0044] Prior to the activation treatment of the carbonized material, the carbonized material may be subjected to primary activation in advance. In this primary activation, the carbonized material is preferably calcined at a temperature of less than 900°C using an activation gas such as water vapor, carbon dioxide, or oxygen.

[0045] The activated carbon 1 having the above characteristics can be produced by appropriately combining the calcination temperature and calcination time in the carbonization method with the activation gas supply amount, temperature rise rate, and maximum activation temperature in the activation method.

[0046] (activated carbon 2) The mesopore volume V1 of activated carbon 2 is set to 0.8 cm from the viewpoint of increasing the input / output characteristics when incorporated into an energy storage element. 3 From the viewpoint of suppressing a decrease in the capacity of the electric storage element, V1 is preferably set to a value larger than 2.5 cm 3 / g or less. The above V1 is more preferably 1.0 cm 3 / g or more 2.0cm 3 / g or less, more preferably 1.2 cm 3 / g or more 1.8cm 3 / g or less.

[0047] On the other hand, the micropore volume V2 of activated carbon 2 is set to 0.8 cm in order to increase the specific surface area of ​​the activated carbon and increase the capacity. 3 From the viewpoint of increasing the density of the activated carbon as an electrode and increasing the capacity per unit volume, V2 is preferably 3.0 cm 3 / g or less. The above V2 is more preferably 1.0 cm 3 / g or greater than 2.5cm 3 / g or less, more preferably 1.5 cm 3 / g or more 2.5cm 3 / g or less.

[0048] The activated carbon 2 having the above-mentioned mesopores and micropores has a higher BET specific surface area than activated carbons used in conventional electric double layer capacitors or lithium ion capacitors. The specific value of the BET specific surface area of ​​the activated carbon 2 is 2,300 m 2 / g or more 4,000m 2 The lower limit of the BET specific surface area is preferably 3,000 m / g or less. 2 / g or more is more preferable, and 3,200m 2 The upper limit of the BET specific surface area is 3,800 m / g or more. 2 / g or less is more preferable. 2 / g or more, a good energy density is easily obtained, while a BET specific surface area of ​​4,000 m 2 When the electrode has a porosity of 0.1g or less, it is not necessary to add a large amount of binder to maintain the strength of the electrode, and therefore the performance per volume of the electrode is improved.

[0049] The activated carbon 2 having the above-mentioned characteristics can be obtained, for example, using the raw materials and processing methods described below.

[0050] The carbon source used as the raw material for activated carbon 2 is not particularly limited as long as it is a carbon source typically used as a raw material for activated carbon, and examples thereof include plant-based raw materials such as wood, wood flour, and coconut shells; fossil-based raw materials such as petroleum pitch and coke; and various synthetic resins such as phenolic resin, furan resin, vinyl chloride resin, vinyl acetate resin, melamine resin, urea resin, and resorcinol resin. Among these raw materials, phenolic resin and furan resin are particularly preferred because they are suitable for producing activated carbon with a high specific surface area.

[0051] Methods for carbonizing these raw materials or heating methods during activation treatment include known methods such as fixed bed, moving bed, fluidized bed, slurry, and rotary kiln. The heating atmosphere is an inert gas such as nitrogen, carbon dioxide, helium, or argon, or a mixture of these inert gases with other gases as the main component. The carbonization temperature is preferably 400 to 700°C, with a lower limit of 450°C or higher, more preferably 500°C or higher, and an upper limit of 650°C or lower. The firing time is preferably about 0.5 to 10 hours.

[0052] Methods for activating the carbonized product after the carbonization treatment include a gas activation method in which the carbonized product is calcined using an activation gas such as water vapor, carbon dioxide, or oxygen, and an alkali metal activation method in which the carbonized product is mixed with an alkali metal compound and then heated. The alkali metal activation method is preferred for producing activated carbon with a high specific surface area.

[0053] In this activation method, the carbide is mixed with an alkali metal compound such as potassium hydroxide (KOH) or sodium hydroxide (NaOH) in a mass ratio of 1:1 or more (the amount of the alkali metal compound is the same as or greater than the amount of the carbide), and then heated in an inert gas atmosphere at a temperature preferably in the range of 600 to 900°C, more preferably 650 to 850°C, for 0.5 to 5 hours. Thereafter, the alkali metal compound is removed by washing with acid and water, and then the mixture is dried.

[0054] The mass ratio of carbide to alkali metal compound (= carbide:alkali metal compound) is preferably 1:1 or more, and since the amount of mesopores increases as the amount of alkali metal compound increases and the amount of pores tends to increase sharply at a mass ratio of around 1:3.5, the mass ratio of carbide to alkali metal compound is preferably 1:3 or more. The amount of pores increases as the amount of alkali metal compound increases, but considering the efficiency of subsequent treatments such as washing, the mass ratio of carbide to alkali metal compound is preferably 1:5.5 or less.

[0055] To increase the micropore volume without increasing the mesopore volume, it is recommended to mix a larger amount of carbide with KOH during activation. To increase both the micropore volume and the mesopore volume, it is recommended to use a larger amount of KOH. To mainly increase the mesopore volume, it is preferable to perform steam activation after alkali activation treatment.

[0056] For V1, V2 and the BET specific surface area of ​​the activated carbon 2, the upper and lower limits of the preferred ranges explained above can be combined arbitrarily.

[0057] (Use of activated carbon) Activated carbon is used as the positive electrode active material, and activated carbons 1 and 2 may each be a single type of activated carbon, or a mixture of two or more types of activated carbons that exhibit the above-mentioned characteristic values ​​of each of the mixtures as a whole.

[0058] The activated carbons 1 and 2 may be used either alone or in combination.

[0059] The positive electrode active material may contain a material other than activated carbons 1 and 2 (for example, activated carbon not having the above-mentioned specific V1 and / or V2, or a material other than activated carbon (for example, a composite oxide of an alkali metal and a transition metal)). The content of activated carbon 1, the content of activated carbon 2, or the total content of activated carbons 1 and 2 is preferably more than 50 mass% of the total positive electrode active material, more preferably 70 mass% or more, even more preferably 90 mass% or more, and even more preferably 100 mass%.

[0060] The content of the positive electrode active material in the positive electrode active material layer is preferably 35% by mass or more and 95% by mass or less, based on the total mass of the positive electrode active material layer in the positive electrode precursor. The lower limit of the content of the positive electrode active material is more preferably 45% by mass or more, and even more preferably 55% by mass or more. The upper limit of the content of the positive electrode active material is more preferably 90% by mass or less, and even more preferably 80% by mass or less. By maintaining the content within this range, favorable charge / discharge characteristics are exhibited.

[0061] -Alkali metal compounds- In this embodiment, the alkali metal compound used is a compound capable of decomposing in the positive electrode precursor to release alkali metal ions. At least one compound selected from the group consisting of carbonates, oxides, hydroxides, fluorides, chlorides, oxalates, iodides, nitrides, sulfides, phosphides, nitrates, sulfates, phosphates, oxalates, formates, and acetates, each of which has an alkali metal ion as a cation, is preferably used. Among these, carbonates, oxides, and hydroxides are more preferred, and alkali metal carbonates are even more preferred because they can be handled in air and have low hygroscopicity. As the alkali metal carbonate, at least one compound selected from the group consisting of lithium carbonate, sodium carbonate, and potassium carbonate is preferably used, and lithium carbonate is even more preferred because of its high capacity per unit weight. The alkali metal compound preferably contains at least 10% by mass of lithium carbonate, based on the total mass of the alkali metal compounds contained in the positive electrode precursor. The alkali metal compound contained in the positive electrode precursor may contain one type or two or more types.

[0062] In addition to the alkali metal compound, the positive electrode precursor of this embodiment may contain one or more alkaline earth metal carbonates, for example, at least one selected from the group consisting of BeCO3, MgCO3, CaCO3, SrCO3, and BaCO3, alkaline earth metal oxides, alkaline earth metal hydroxides, alkaline earth metal halides, alkaline earth metal oxalates, and alkaline earth metal carboxylates.

[0063] The content of the alkali metal compound in the positive electrode active material layer is preferably 5% by mass or more and 50% by mass or less, based on the total mass of the positive electrode active material layer in the positive electrode precursor. The lower limit of the content of the alkali metal compound is more preferably 10% by mass or more, and even more preferably 15% by mass or more. The upper limit of the content of the alkali metal compound is more preferably 45% by mass or less, and even more preferably 40% by mass or less.

[0064] If the content of the alkali metal compound in the positive electrode active material layer is 5% by mass or more, a sufficient amount of alkali metal ions can be secured for pre-doping into the negative electrode, and an appropriate degree of porosity can be imparted to the positive electrode, improving the input / output characteristics of the nonaqueous hybrid capacitor. If the content of the alkali metal compound in the positive electrode active material layer is 50% by mass or less, the electronic conductivity of the positive electrode precursor is increased, accelerating the decomposition of the alkali metal compound, thereby completing pre-doping in a short time and producing a nonaqueous hybrid capacitor with a high energy density.

[0065] When the positive electrode precursor contains the alkaline earth metal compound in addition to the alkali metal compound, the positive electrode precursor is preferably produced so that the total mass of the alkali metal compound and the alkaline earth metal compound is 5 mass % or more and 50 mass % or less, based on the total mass of the positive electrode active material layer in the positive electrode precursor.

[0066] (Average particle size of alkali metal compound and positive electrode active material) In the positive electrode precursor of this embodiment, when the average particle size of the alkali metal compound is designated as X1, it is preferable that X1 be 0.1 μm≦X1≦10 μm. The lower limit of X1 is more preferably 0.3 μm or more, and even more preferably 0.5 μm or more, and the upper limit of X1 is more preferably 5 μm or less, and even more preferably 3 μm or less. The upper and lower limits of X1 can be combined in any manner.

[0067] If X1 is 0.1 μm or more, the dispersion uniformity of the alkali metal compound in the positive electrode precursor is excellent. If X1 is 10 μm or less, since the surface area of the alkali metal compound increases, the decomposition reaction proceeds efficiently when the positive electrode precursor is incorporated for a non-aqueous hybrid capacitor.

[0068] Also, in the positive electrode precursor of the present embodiment, when the average particle diameter of the positive electrode active material is Y1, it is preferably 2 μm ≤ Y1 ≤ 20 μm. As the lower limit of Y1, it is more preferably 2.5 μm or more, and even more preferably 3 μm or more. As the upper limit of Y1, it is more preferably 15 μm or less, and even more preferably 10 μm or less. The upper and lower limits of Y1 can be arbitrarily combined.

[0069] If Y1 is 2 μm or more, the electrode density of the positive electrode precursor can be maintained high, and thus a high energy density can be obtained. If Y1 is 20 μm or less, since the reaction area with electrolyte ions increases, high input / output characteristics can be exhibited.

[0070] Furthermore, in the positive electrode precursor of the present embodiment, the relationship between the average particle diameters of the alkali metal compound and the positive electrode active material is preferably X1 < Y1. If X1 < Y1, the dispersion uniformity of the alkali metal compound and the positive electrode active material in the positive electrode precursor is excellent, and since the alkali metal compound fills the gaps generated between the positive electrode active materials inside the positive electrode precursor, the electron conductivity between the positive electrode active materials can be ensured while increasing the energy density.

[0071] -Binder- The positive electrode active material layer contained in the positive electrode precursor of the present embodiment contains a binder. The type of the binder is not particularly limited, and examples thereof include rubber-based polymers, fluorine-containing substances, polyimides, etc., but it is preferable to contain a rubber-based polymer and / or a fluorine-containing substance. The binder contained in the positive electrode active material layer may be used alone or in combination of two or more.

[0072] When the positive electrode precursor is incorporated into a non-aqueous hybrid capacitor, it is preferable to apply a voltage between the positive electrode precursor and the negative electrode during pre-doping. The binder contained in the positive electrode active material layer is 4.3 V (vs. Li / Li + ) or more, and + ) or more is more preferable, and 4.5V (vs. Li / Li + ) or more is more preferable. The oxidation resistance of the binder is 4.3V (vs. Li / Li + ) or more, oxidative decomposition of the binder can be suppressed when a voltage is applied during pre-doping, and sufficient electrode strength can be ensured even after pre-doping.

[0073] In this specification, the oxidation resistance of a binder is a value obtained by the following method. First, a slurry containing carbon black, carboxymethyl cellulose, and a binder is applied to a platinum foil and dried to prepare a measurement electrode. A measurement cell is prepared using the measurement electrode as the working electrode, a Li metal foil as the counter electrode and a reference electrode, a separator, and a non-aqueous electrolyte. Linear sweep voltammetry is measured at a sweep rate of 2 mV / sec, a voltage range of 3 V to 5.4 V, and a temperature of 25°C, and a current of 50 μA / cm is obtained. 2 The potential at which a current response of 0.01 is observed is taken as the oxidation resistance value.

[0074] (rubber-based polymer) When a rubber-based polymer is included as a binder in the positive electrode active material layer of this embodiment, examples of the rubber-based polymer include diene polymers, acrylic polymers, and fluororubbers. From the viewpoints of high binding ability with the positive electrode active material and excellent electrode strength or flexibility, diene polymers or acrylic polymers are preferred. Among these, acrylic latex is more preferred from the viewpoints of not containing unsaturated bonds in the polymer main chain and having high electrochemical stability. The acrylic latex is not particularly limited, but is preferably a polymer of acrylic acid ester and / or methacrylic acid ester, or a copolymer of these with a monomer copolymerizable therewith.

[0075] The binder for the positive electrode active material layer of the present embodiment may be the rubber-based polymer containing fluorine, the fluorine-containing material and the rubber-based polymer may be used in combination, or composite particles of the fluorine-containing material and the rubber-based polymer may be used.

[0076] (Fluorine-containing materials) When a fluorine-containing material is contained as a binder in the positive electrode active material layer of the present embodiment, the fluorine-containing material is preferably PVdF (polyvinylidene fluoride) or PTFE (polytetrafluoroethylene) from the viewpoints of oxidation resistance and high peel strength, and is more preferably PVdF (polyvinylidene fluoride) from the viewpoints of easy thinning of the positive electrode precursor and high input / output when incorporated into a nonaqueous hybrid capacitor.

[0077] The weight-average molecular weight of the binder contained in the positive electrode active material layer of this embodiment is preferably 500,000 or more and 1,800,000 or less. The upper limit of the weight-average molecular weight of the binder is preferably 1,600,000 or less, more preferably 1,450,000 or less, and even more preferably 1,300,000 or less, and the lower limit is preferably 600,000 or more, more preferably 700,000 or more, and even more preferably 800,000 or more. The upper and lower limits of the weight-average molecular weight of the binder can be combined in any manner.

[0078] When the weight-average molecular weight of the binder contained in the positive electrode active material layer is 500,000 or more, the binder is less likely to penetrate into the pores of the positive electrode active material, allowing the added binder to efficiently bind the components of the positive electrode active material layer together. Furthermore, even if voids remain in the electrode after pre-doping due to the alkali metal compound's elimination, high peel strength can be ensured due to the long molecular chains of the binder. When the weight-average molecular weight of the binder is 1,800,000 or less, the insulating binder does not inhibit the entry and exit and diffusion of ions into the positive electrode active material when incorporated into a non-aqueous hybrid capacitor, thereby achieving high input / output characteristics. Furthermore, pre-doping is accelerated by promoting the diffusion of alkali metal ions derived from the oxidative decomposition of the alkali metal compound.

[0079] The amount of binder used in the positive electrode active material layer is preferably 1% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 27% by mass or less, and even more preferably 5% by mass or more and 25% by mass or less, relative to 100% by mass of the positive electrode active material. If the amount of binder used is 1% by mass or more, sufficient electrode strength is exhibited. If the amount of binder used is 30% by mass or less, the ingress and egress of ions into and diffusion from the positive electrode active material are not hindered, high input / output characteristics are exhibited, and pre-doping is also promoted because the diffusion of alkali metal ions derived from the oxidative decomposition of the alkali metal compound is promoted during pre-doping.

[0080] -Water-soluble polymer- The positive electrode active material layer contained in the positive electrode precursor of this embodiment contains a water-soluble polymer as a dispersion stabilizer. The water-soluble polymer includes carboxymethyl cellulose. In this specification, carboxymethyl cellulose refers to carboxymethyl cellulose or a salt thereof. Examples of the salt of carboxymethyl cellulose include ammonium salts and alkali metal salts, but sodium salt of carboxymethyl cellulose is preferred.

[0081] In a case where a positive electrode precursor is obtained by dispersing or dissolving a positive electrode active material, an alkali metal compound, a binder, a water-soluble polymer, and other optional components used as needed in water to prepare a positive electrode slurry, applying this positive electrode slurry to one or both surfaces of a positive electrode current collector to form a coating film, and drying this, the skeleton of carboxymethyl cellulose becomes a hydrophobic moiety and the terminal groups become hydrophilic moieties in the positive electrode slurry, and the hydrophobic moieties of the carboxymethyl cellulose adsorb to a hydrophobic substance such as a carbon material, thereby functioning like a surfactant.

[0082] The degree of etherification of carboxymethyl cellulose is a value that indicates the amount of hydrophobic moieties and hydrophilic moieties, and is preferably 0.5 to 1.0, with the upper limit being more preferably 0.9 or less, and even more preferably 0.8 or less, and the lower limit being more preferably 0.55 or more, and even more preferably 0.6 or more. The upper and lower limits of the degree of etherification of the carboxymethyl cellulose can be combined arbitrarily. If the degree of etherification is 0.5 or higher, when added to a positive electrode slurry, the carboxymethyl cellulose dissolves uniformly without any undissolved matter such as gel, and does not inhibit the movement and diffusion of ions into and out of the positive electrode active material, resulting in high input / output characteristics. If the degree of etherification is 1.0 or lower, the carboxymethyl cellulose is sufficiently adsorbed onto the surface of the carbon material in the positive electrode slurry, and the carboxymethyl cellulose molecules are bound together with a binder, ensuring sufficient electrode strength. Furthermore, the carbon material and alkali metal compound are uniformly distributed within the positive electrode active material layer without localization. When incorporated into a nonaqueous hybrid capacitor, charge / discharge reactions proceed uniformly within the positive electrode active material layer, and side reactions are suppressed because the surface of the carbon material is adequately coated with carboxymethyl cellulose, resulting in excellent durability. The degree of etherification in this specification is a value obtained by ashing titration. Approximately 1 g of a carboxymethyl cellulose sample is accurately weighed, placed in a porcelain or platinum crucible, and incinerated at 600°C. The incinerated material is transferred to a 500 ml beaker, and 250 ml of water and 50 ml of 0.05 mol / L (0.1 N) aqueous sulfuric acid solution are added and boiled for 30 minutes. After cooling, the excess acid is back-titrated with 0.1 mol / L (0.1 N) aqueous sodium hydroxide solution using phenolphthalein as an indicator. The measurement results are used to calculate the degree of etherification using the following formula. Degree of etherification = 162 x A / (10000 - 80 x A) A = (a × f1 - bf2) / weight of sample (g) a: Amount (mL) of 0.05 mol / L (0.1 N) sulfuric acid solution used b: Amount (mL) of 0.1 mol / L (0.1N) sodium hydroxide solution used f1: Potency of 0.05 mol / L (0.1 N) sulfuric acid solution f2: Potency of 0.1 mol / L (0.1N) sodium hydroxide solution

[0083] The viscosity of a 1% by mass aqueous solution of carboxymethyl cellulose (25°C) is preferably 10 mPa·s or more and 6000 mPa·s or less, with an upper limit of 4500 mPa·s or less being more preferred, and 3000 mPa·s or less being even more preferred, and a lower limit of 50 mPa·s or more and even more preferred, and 300 mPa·s or more being even more preferred. The upper and lower limits of the viscosity of a 1% by mass aqueous solution of carboxymethyl cellulose (25°C) can be arbitrarily combined. When the viscosity of a 1% by mass aqueous solution (25°C) is 10 mPa·s or more, the carboxymethyl cellulose bonds with each other, ensuring sufficient electrode strength and excellent durability when incorporated into a non-aqueous hybrid capacitor. When the viscosity of a 1% by mass aqueous solution (25°C) is 6000 mPa·s or less, the carboxymethyl cellulose does not inhibit the ingress and egress of ions into and diffusion from the positive electrode active material when incorporated into a non-aqueous hybrid capacitor, resulting in high input / output characteristics. Furthermore, the diffusion of alkali metal ions resulting from the oxidative decomposition of the alkali metal compound is promoted during pre-doping, thereby accelerating pre-doping. Here, the viscosity of a 1% by mass aqueous solution (25°C) in this specification is a value obtained by the following method. First, the amount of water contained in a carboxymethyl cellulose sample is determined. Approximately 3 g of the sample is precisely weighed and dried at 105°C for 4 hours, after which the water content (% by mass) is calculated using the following formula: Moisture content (mass%) = (weight loss (g) - sample weight (g)) x 100 Next, approximately 2.5 g of carboxymethyl cellulose sample was weighed out and transferred to a 300 mL container with a lid. The amount of water calculated using the formula "sample weight (g) x (99 - water content (mass%))" was added, and the solution was stirred and left overnight to completely dissolve, yielding a 1% by mass aqueous solution of carboxymethyl cellulose. The viscosity of the resulting solution was measured after 3 minutes at 25°C with a rotor speed of 60 rpm using a BM-type viscometer (single-cylinder rotational viscometer) in accordance with JIS Z8803.

[0084] The water-soluble polymer contained in the positive electrode active material layer may be a single type of carboxymethyl cellulose, or two or more types of carboxymethyl cellulose, or a combination of water-soluble polymers other than carboxymethyl cellulose. Examples of water-soluble polymers other than carboxymethyl cellulose that can be used include PVP (polyvinylpyrrolidone) and PVA (polyvinyl alcohol).

[0085] The amount of the water-soluble polymer contained in the positive electrode active material layer is preferably 0.5% by mass or more and 10.0% by mass or less, based on the total mass of the carbon material contained in the positive electrode active material layer. The upper limit of the amount of the water-soluble polymer used is more preferably 9.0% by mass or less, and even more preferably 8.0% by mass or less, and the lower limit is more preferably 1.5% by mass or more, and even more preferably 2.5% by mass or more. The upper and lower limits of the amount of the water-soluble polymer used can be combined in any manner. When the amount of water-soluble polymer used is 0.5% by mass or more, the carbon material and alkali metal compound can be uniformly distributed within the positive electrode active material layer without localization, and when incorporated into a nonaqueous hybrid capacitor, charge / discharge reactions proceed uniformly within the positive electrode active material layer. Side reactions are also suppressed because the surface of the carbon material is moderately coated with the water-soluble polymer, resulting in excellent durability. When the amount of water-soluble polymer used is 10.0% by mass or less, the water-soluble polymer acts as an interparticle crosslinker for the carbon material, preventing particle aggregation. This allows the carbon material to be uniformly distributed within the positive electrode active material layer, preventing the inflow / outflow and diffusion of ions into the positive electrode active material and resulting in high input / output characteristics.

[0086] In this embodiment, as described below, controlling the state of the carbon material containing activated carbon, which is the positive electrode active material in the positive electrode active material layer of the positive electrode precursor and the positive electrode slurry, is important. When the positive electrode precursor is incorporated into a nonaqueous hybrid capacitor, the state of carboxymethyl cellulose adsorbed on the carbon material surface determines the performance of the nonaqueous hybrid capacitor. The state of carboxymethyl cellulose adsorbed on the carbon material surface is significantly affected by the constituent materials of the positive electrode active material layer and the positive electrode slurry, particularly the combination of activated carbon and carboxymethyl cellulose. The degree of etherification of the carboxymethyl cellulose, the viscosity of a 1% by mass aqueous solution (25°C), and the amount used are important factors. Among these, controlling the degree of etherification, which is an indicator of the amount of hydrophobic and hydrophilic moieties, is particularly important, as described above, from the perspective that the hydrophobic moieties of carboxymethyl cellulose adsorb to hydrophobic materials such as carbon materials and function like surfactants.

[0087] -Optional components of the positive electrode active material layer- The positive electrode active material layer of the positive electrode precursor in this embodiment may contain optional components such as a conductive filler in addition to the positive electrode active material, alkali metal compound, binder, and water-soluble polymer, as needed.

[0088] The conductive filler is not particularly limited, and examples thereof include acetylene black, ketjen black, furnace black, vapor-grown carbon fiber, graphite, carbon nanotubes, and mixtures thereof. The amount of conductive filler used in the positive electrode active material layer of the positive electrode precursor is preferably more than 0 parts by mass and less than 30 parts by mass, more preferably 0.01 parts by mass or more and less than 20 parts by mass, and even more preferably 1 part by mass or more and less than 15 parts by mass, per 100 parts by mass of the positive electrode active material. The conductive filler promotes oxidative decomposition during pre-doping by contacting with an alkali metal compound. Furthermore, from the viewpoint of high input / output characteristics, the positive electrode active material layer preferably contains a conductive filler. When the amount of conductive filler used is 30 parts by mass or less, the content of the positive electrode active material in the positive electrode active material layer is increased, thereby ensuring the energy density per volume of the positive electrode active material layer.

[0089] [Positive electrode current collector] The material for the positive electrode current collector in this embodiment is not particularly limited as long as it has high electronic conductivity and is not susceptible to deterioration due to elution in the electrolytic solution or reaction with the electrolyte or ions, etc., and is preferably a metal foil. Aluminum foil is particularly preferred as the metal foil for the positive electrode current collector.

[0090] The positive electrode current collector may be a metal foil having no irregularities or through holes, or may be a metal foil having irregularities that have been subjected to embossing, chemical etching, electrolytic deposition, blasting, or the like, or may be a metal foil having through holes such as expanded metal, punched metal, or etched foil. Among these, metal foil without through holes is preferred for the positive electrode current collector, as it is cheaper to manufacture, easier to make a thin film, which contributes to a high energy density, and lowers current collection resistance, resulting in high input / output characteristics.

[0091] The thickness of the positive electrode current collector is not particularly limited as long as it can sufficiently maintain the shape and strength of the positive electrode, and is preferably, for example, 1 to 100 μm.

[0092] [Positive electrode slurry] The positive electrode slurry according to the present invention is a slurry containing a positive electrode active material, an alkali metal compound other than the positive electrode active material, a binder, a water-soluble polymer, and a solvent, wherein the positive electrode active material is a carbon material, the carbon material includes activated carbon, and the water-soluble polymer includes carboxymethyl cellulose. The slurry is alkaline with a pH of 9.0 or higher, and the slurry is heated at a shear rate of 5 s -1 , 50s -1 , 500s -1 , and 2000s -1where η1 (mPa·s), η2 (mPa·s), η3 (mPa·s), and η4 (mPa·s) are the viscosities at η1 / η1 and η2 / η1, respectively, and 0.10≦η2 / η1≦1.00, 0.10≦η3 / η2≦1.00, and 0.10≦η4 / η3≦1.00. The slurry is dried to remove the solvent, and the solid is immersed in water for 24 hours. A sodium hydroxide solution is added to the solid, and the solid is then extracted. The total amount of acidic functional groups in the solid is calculated by back titration with hydrochloric acid and is 0.15 mmol / g or more and 2.00 mmol / g or less by weight of the solid.

[0093] The positive electrode slurry according to the present embodiment may be in the form of a known slurry, or may be in the form of a known suspension, dispersion, emulsion, composition, or mixture. The positive electrode slurry according to the present embodiment may be simply referred to as a coating liquid, coating liquid, or the like.

[0094] The positive electrode active material layer contained in the positive electrode precursor in this embodiment is constituted by the entire solid content of the positive electrode slurry excluding the solvent. That is, the positive electrode slurry contains the positive electrode active material made of a carbon material including activated carbon, an alkali metal compound other than the positive electrode active material, a water-soluble polymer including carboxymethyl cellulose, and a binder, as well as a solvent. Furthermore, the positive electrode slurry may contain optional components such as a pH adjuster in addition to the conductive filler in the positive electrode active material layer, as needed.

[0095] -solvent- The positive electrode slurry of this embodiment contains a solvent. The type of solvent is not particularly limited, and an organic solvent medium and / or an aqueous medium is used depending on the type of binder. However, since the positive electrode slurry of this embodiment contains a water-soluble polymer, it is preferable to use an aqueous medium.

[0096] When an aqueous medium is used as the solvent for the positive electrode slurry of this embodiment, the water content is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and most preferably 100% by mass, based on the total mass of the solvent in the positive electrode slurry. If the water content is 50% by mass or more, solids in the positive electrode slurry are less likely to settle. The water used as the solvent for the positive electrode slurry is preferably ion-exchanged water or ultrapure water treated with an ion exchange resin or a reverse osmosis membrane water purification system.

[0097] When an aqueous medium is contained as a solvent, a non-aqueous liquid medium other than water may be contained. Examples of the non-aqueous liquid medium include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, and sulfone compounds, and preferably alcohols such as methanol, ethanol, propanol, isopropanol, n-butanol, and t-butanol. One or more selected from these may be used.

[0098] -Optional components of positive electrode slurry- The positive electrode slurry in this embodiment is alkaline with a pH of 9.0 or higher. However, not only does this decrease the molecular weight of the binder, but under conditions where the positive electrode slurry exhibits strong alkalinity when the positive electrode precursor is produced, corrosion of the positive electrode current collector is accelerated, which is thought to result in a shortened lifespan of the nonaqueous hybrid capacitor. Therefore, when the positive electrode slurry exhibits strong alkalinity, it is preferable to add a pH adjuster. The type of pH adjuster is not particularly limited, and either a strong acid or a weak acid can be used. Furthermore, the strong acid or weak acid may be an inorganic acid or an organic acid.

[0099] For example, inorganic acids include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and carbonic acid, while organic acids include acetic acid, oxalic acid, and citric acid. Among these, acids that decompose or volatilize during the manufacturing process of the positive electrode precursor and / or nonaqueous hybrid capacitor are preferred, such as acetic acid and hydrochloric acid. The amount of pH adjuster used in the positive electrode slurry is preferably greater than 0% by mass, or 0.1% by mass or more and 1% by mass or less, based on the total mass of all solids in the positive electrode slurry. Using an amount of pH adjuster of 1% by mass or less reduces the amount of residual pH adjuster.

[0100] [Production of positive electrode slurry] In this embodiment, the positive electrode slurry for the nonaqueous hybrid capacitor can be produced by a known production technique for electrode slurries in lithium ion batteries, electric double layer capacitors, etc. For example, the positive electrode slurry is prepared by dispersing or dissolving a positive electrode active material, an alkali metal compound, a binder, a water-soluble polymer, and other optional components used as needed in a solvent.

[0101] The positive electrode slurry may be prepared by dry-blending some or all of various material powders, including the positive electrode active material, followed by adding a solvent and / or a liquid or slurry-like substance in which a binder or dispersion stabilizer is dissolved or dispersed. Alternatively, the positive electrode slurry may be prepared by adding various material powders, including the positive electrode active material, to a liquid or slurry-like substance in which a binder or dispersion stabilizer is dissolved or dispersed in a solvent. As a dry-blending method, for example, a ball mill may be used to premix the positive electrode active material, the alkali metal compound, and optionally, a conductive filler, thereby coating the low-conductivity alkali metal compound with the conductive filler. Premixing facilitates decomposition of the alkali metal compound in the positive electrode precursor during the pre-doping process described below. If the positive electrode slurry becomes strongly alkaline due to the addition of the alkali metal compound, a pH adjuster may be added as needed.

[0102] The method for dispersing the positive electrode slurry is not particularly limited, and preferably, a disperser such as a homodisper, a multi-axis disperser, a planetary mixer, or a thin film rotary high-speed mixer can be used. To obtain a positive electrode slurry in a well-dispersed state, it is preferable to disperse the slurry 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 various materials are less likely to be destroyed by heat or shear force due to dispersion, and re-aggregation is less likely to occur.

[0103] [Production of positive electrode precursor] In this embodiment, the positive electrode precursor that serves as the positive electrode of the nonaqueous hybrid capacitor can be manufactured by known electrode manufacturing techniques for lithium ion batteries, electric double layer capacitors, etc. For example, the positive electrode precursor can be obtained by applying the positive electrode slurry to one or both sides of a positive electrode current collector to form a coating film, and then drying the coating film. The obtained positive electrode precursor may be pressed to adjust the thickness or bulk density of the positive electrode active material layer.

[0104] The method for forming the coating film of the positive electrode precursor is not particularly limited, and a coating machine such as a die coater, comma coater, knife coater, or gravure coater can be suitably used. The coating film may be formed by single-layer coating or multi-layer coating. In the case of multi-layer coating, the positive electrode slurry composition may be adjusted so that the content of the alkali metal compound in each layer of the coating film is different. The coating speed is preferably 0.1 m / min to 100 m / min, more preferably 0.5 m / min to 70 m / min, and even more preferably 1 m / min to 50 m / min. A coating speed of 0.1 m / min or higher ensures stable coating. A coating speed of 100 m / min or lower ensures sufficient coating accuracy.

[0105] The method for drying the coating film of the positive electrode precursor is not particularly limited, and suitable drying methods include hot air drying and infrared (IR) drying. The coating film may be dried at a single temperature or at multiple stages with varying temperatures. The coating film may also be dried using a combination of multiple drying methods. The drying temperature is preferably 25°C or higher and 200°C or lower, more preferably 40°C or higher and 180°C or lower, and even more preferably 50°C or higher and 160°C or lower. A drying temperature of 25°C or higher allows the solvent in the coating film to be sufficiently volatilized. A drying temperature of 200°C or lower can prevent cracking of the coating film due to rapid solvent evaporation, uneven distribution of the binder due to migration, and oxidation of the positive electrode current collector and the positive electrode active material layer.

[0106] The method for pressing the positive electrode precursor is not particularly limited, and a press such as a hydraulic press, a vacuum press, etc. can be suitably used. The thickness, bulk density, and electrode strength of the positive electrode active material layer can be adjusted by the press pressure, gap, and surface temperature of the press part, which will be described later.

[0107] The pressing pressure is preferably 0.5 kN / cm or more and 20 kN / cm or less, more preferably 1 kN / cm or more and 10 kN / cm or less, and even more preferably 2 kN / cm or more and 7 kN / cm or less. If the pressing pressure is 0.5 kN / cm or more, the electrode strength can be sufficiently increased. 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 thickness and bulk density can be adjusted to the desired value.

[0108] Those skilled in the art can set the gap between the press rolls to any value depending on the thickness of the dried positive electrode precursor so as to achieve a desired thickness and bulk density of the positive electrode active material layer, and can set the pressing speed to any speed at which bending or wrinkling is unlikely to occur in the positive electrode precursor.

[0109] The surface temperature of the press part may be room temperature, or the press part may be heated as necessary. When heated, the lower limit of the surface temperature of the press part is preferably at least 60°C below the melting point of the binder used, more preferably at least 45°C below the melting point, and even more preferably at least 30°C below the melting point. When heated, the upper limit of the surface temperature of the press part is preferably at most 50°C above the melting point of the binder used, more preferably at most 30°C above the melting point, and even more preferably at most 20°C above the melting point. For example, when PVdF (polyvinylidene fluoride: melting point 150°C) is used as the binder, the surface temperature of the press part is preferably at least 90°C and no more than 200°C, more preferably at least 105°C and no more than 180°C, and even more preferably at least 120°C and no more than 170°C.

[0110] The melting point of the binder can be determined from the endothermic peak position in DSC (Differential Scanning Calorimetry). For example, using a PerkinElmer DSC7 differential scanning calorimeter, 10 mg of sample resin is placed in the measurement cell, and the temperature is raised from 30°C to 250°C at a rate of 10°C / min in a nitrogen gas atmosphere. The endothermic peak temperature during the temperature rise process is the melting point.

[0111] Pressing may be performed multiple times while changing the conditions of press pressure, gap, speed, and surface temperature of the press part.

[0112] [Physical properties of positive electrode slurry] In this embodiment, as described below, after assembling a nonaqueous hybrid capacitor, applying a voltage between a positive electrode precursor containing an alkali metal compound and a negative electrode decomposes the alkali metal compound in the positive electrode precursor, thereby pre-doping the negative electrode with alkali metal ions. At this time, it is very important that the alkali metal compound is uniformly decomposed within the positive electrode precursor. That is, uniform pre-doping within the negative electrode electrode suppresses negative electrode potential unevenness and also suppresses the remnants of alkali metal compounds that were not completely decomposed within the positive electrode after pre-doping, resulting in a nonaqueous hybrid capacitor with excellent high-temperature durability. Furthermore, since alkali metal compounds are insulators, if they remain in the positive electrode after pre-doping, they will inhibit the electron conduction of the positive electrode and cause a decrease in input / output characteristics. Therefore, it is important that the alkali metal compound is uniformly distributed within the positive electrode precursor without localization. Here, in order to increase uniformity within the positive electrode precursor, high dispersion uniformity of the solids, particularly the alkali metal compound, is required even within the positive electrode slurry. Furthermore, in this embodiment, as described below, it is important to control the state of the carbon material containing activated carbon, which is the positive electrode active material in the positive electrode active material layer of the positive electrode precursor, and when the positive electrode precursor is incorporated into a nonaqueous hybrid capacitor, the state of carboxymethyl cellulose adsorbed on the surface of the carbon material determines the performance of the nonaqueous hybrid capacitor. To achieve this state in the positive electrode precursor, it is important to ensure that the carboxymethyl cellulose is not present in excess in the liquid in the positive electrode slurry and is appropriately adsorbed on the surface of the carbon material.

[0113] -Viscosity properties- The positive electrode slurry of this embodiment is prepared by shearing the slurry at a shear rate of 5 s -1 , 50s -1 , 500s -1 , and 2000s -1When the viscosities at η1 (mPa·s), η2 (mPa·s), η3 (mPa·s), and η4 (mPa·s) are respectively, 0.10≦η2 / η1≦1.00, 0.10≦η3 / η2≦1.00, and 0.10≦η4 / η3≦1.00. The upper limit of η2 / η1 is preferably 0.95 or less, more preferably 0.90 or less, and even more preferably 0.85 or less. On the other hand, the lower limit of η2 / η1 is preferably 0.15 or more, more preferably 0.20 or more, and even more preferably 0.25 or more. The upper limit of η3 / η2 is preferably 0.95 or less, more preferably 0.90 or less, and even more preferably 0.85 or less. On the other hand, the lower limit of η3 / η2 is preferably 0.20 or more, more preferably 0.30 or more, and even more preferably 0.35 or more. The upper limit of η4 / η3 is preferably 0.95 or less, more preferably 0.90 or less, and even more preferably 0.85 or less. On the other hand, the lower limit of η4 / η3 is preferably 0.20 or more, more preferably 0.30 or more, and even more preferably 0.35 or more. The upper and lower limits of the above η2 / η1, η3 / η2, and η4 / η3 can be combined arbitrarily.

[0114] In this embodiment, as described above, the correlations η / η, η / η, and η / η are defined as indicators of the state of carboxymethyl cellulose adsorption on the carbon material surface in the positive electrode slurry, which influences the performance of the nonaqueous hybrid capacitor. In this embodiment, when the viscosity of the positive electrode slurry increases with increasing shear rate, i.e., when the positive electrode slurry exhibits dilatant fluid-like behavior, it is presumed that this reflects the state in which carboxymethyl cellulose is insufficiently adsorbed onto the carbon material surface or is easily desorbed and released into the liquid, and that increasing the shear rate in this state, i.e., applying an external force, causes the carboxymethyl cellulose to re-adsorb onto the carbon material surface or causes aggregation of carboxymethyl cellulose molecules in the liquid. An ideal positive electrode slurry is a pseudoplastic fluid, in which shear rate and viscosity are negatively correlated, and the viscosity decreases as the shear rate increases.

[0115] If η2 / η1, η3 / η2, and η4 / η3 are 0.10 or greater, the change in viscosity with respect to shear rate is suppressed, which enables uniform distribution of the coating film in the coating length and coating width directions when forming a coating film of the positive electrode precursor using a coater. This also enables uniform pre-doping of alkali metal ions into the negative electrode when assembling a nonaqueous hybrid capacitor, resulting in excellent high input / output characteristics and high-temperature storage characteristics. On the other hand, if η2 / η1, η3 / η2, and η4 / η3 are 1.00 or less, carboxymethyl cellulose is sufficiently adsorbed onto the surface of the carbon material, thereby suppressing aggregation of carbon material particles due to a lack of carboxymethyl cellulose on the surface of the carbon material, resulting in excellent dispersion stability of the positive electrode slurry. Furthermore, by binding the carboxymethyl cellulose particles together in the positive electrode precursor with a binder, sufficient electrode strength can be ensured, and the carbon material and alkali metal compound can be uniformly distributed within the positive electrode active material layer without localization. Therefore, when the positive electrode is incorporated into a nonaqueous hybrid capacitor, charge / discharge reactions proceed uniformly within the positive electrode active material layer. Furthermore, since the surface of the carbon material is moderately coated with carboxymethyl cellulose, side reactions are also suppressed, resulting in excellent high-temperature durability.

[0116] The viscosity (ηb) of the positive electrode slurry is preferably 1,000 mPa·s or more and 20,000 mPa·s or less, more preferably 1,500 mPa·s or more and 10,000 mPa·s or less, and even more preferably 1,700 mPa·s or more and 5,000 mPa·s or less. If the viscosity (ηb) is 1,000 mPa·s or more, dripping during coating film formation is suppressed, and the width and thickness of the coating film can be well controlled. If the viscosity (ηb) is 20,000 mPa·s or less, stable coating can be achieved with little pressure loss in the flow path of the positive electrode slurry when using a coating machine, and the coating film thickness can be controlled to a desired value or less.

[0117] The TI value (thixotropy index value) of the positive electrode slurry is preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.5 or more. If the TI value is 1.1 or more, the coating width and thickness can be well controlled.

[0118] The positive electrode slurry was stirred in a container and then allowed to stand for 7 days. When the total volume of the positive electrode slurry was divided into three parts in the height direction, the viscosity of the top layer liquid and the viscosity of the bottom layer liquid were each η U , η L (mPa·s), 0.50≦η U / η L It is preferable that η is ≦1.00. U / η L The upper limit of η may be 0.98 or less or 0.95 or less. U / η L The lower limit of η is preferably 0.60 or more, more preferably 0.70 or more, even more preferably 0.80 or more, and even more preferably 0.85 or more. U / η L The upper and lower limits can be combined arbitrarily.

[0119] η U / η L If η is 0.50 or more, the dispersion stability of the positive electrode slurry is high, making it easy to handle during storage, and when forming a coating film of the positive electrode precursor, it becomes possible to uniformly distribute the constituent materials of the positive electrode active material layer in the direction of the coating film thickness, and when incorporated into a non-aqueous hybrid capacitor, it will have excellent high input / output characteristics and high-temperature storage characteristics. U / η L If the ratio is 1.00 or less, the solid content in the positive electrode slurry is sufficiently dispersed, and when the positive electrode precursor is incorporated into a non-aqueous hybrid capacitor, the alkali metal compound is sufficiently decomposed by pre-doping, resulting in high energy density and excellent high-temperature storage characteristics.

[0120] -Other physical properties- The positive electrode slurry of this embodiment is alkaline with a pH of 9.0 or higher. The upper limit of the pH is preferably 12.0 or lower, more preferably 11.5 or lower, and even more preferably 11.0 or lower. On the other hand, the lower limit of the pH is preferably 9.2 or higher, more preferably 9.4 or higher, and even more preferably 9.6 or higher. The upper and lower limits of the pH can be combined in any manner.

[0121] If the pH is 9.0 or higher, the alkali metal compound is not excessively neutralized and can exist as an alkali metal compound in the positive electrode slurry. Therefore, when the positive electrode precursor is produced, it can exist as an alkali metal compound in the positive electrode active material layer. When the positive electrode precursor is incorporated into a nonaqueous hybrid capacitor, the alkali metal compound is sufficiently decomposed by pre-doping, resulting in excellent high-temperature durability. On the other hand, if the pH is 12.0 or lower, molecular weight reduction due to depolymerization of the binder or water-soluble polymer is suppressed, and aggregation of carbon material particles is suppressed, resulting in a nonaqueous hybrid capacitor with high input / output characteristics. Furthermore, sufficient electrode strength is ensured. When the positive electrode precursor is produced, corrosion of the positive electrode current collector due to the alkalinity of the positive electrode slurry is suppressed, resulting in a nonaqueous hybrid capacitor with excellent high-temperature durability.

[0122] The positive electrode slurry is prepared by mixing the total mass of the positive electrode slurry with the total mass of the solid components excluding the solvent in a ratio of W T When expressed as mass%, 10≦W T It is preferable that W is ≦50. T The upper limit of W is more preferably 47.5 or less, and even more preferably 45 or less. T The lower limit is more preferably at least 15, even more preferably at least 20, and even more preferably at least 25. The upper and lower limits of WT can be combined arbitrarily.

[0123] W T If W is 10 or more, the degree of freedom of movement of the particles or polymers that are the solid content in the positive electrode slurry is suppressed, so that sedimentation is suppressed and dispersion uniformity can be maintained. In addition, the process loads of drying the coating film during the formation of the positive electrode precursor and removing the solvent during the assembly of the non-aqueous hybrid capacitor are reduced, so that productivity can be maintained. T When the value is 50 or less, the coating thickness can be controlled to a desired value or less during the formation of the positive electrode precursor, and unevenness in the coating surface can be suppressed. Therefore, even when the nonaqueous hybrid capacitor is assembled, the decomposition uniformity of the alkali metal compound can be maintained, and the high-temperature storage characteristics are excellent.

[0124] The degree of dispersion of the positive electrode slurry is preferably 0.1 μm or more and 100 μm or less, as measured with a particle gauge. The upper limit of the degree of dispersion is more preferably 80 μm or less, and even more preferably 50 μm or less. A particle size of less than 0.1 μm results in a size equal to or smaller than the particle diameter of the powdered materials, including the positive electrode active material, which is undesirable because the materials are crushed during the preparation of the positive electrode slurry. A particle size of 100 μm or less can maintain uniform dispersion of the positive electrode slurry, minimize clogging during discharge of the positive electrode slurry, and minimize the occurrence of streaks in the coating film, allowing for stable coating.

[0125] The positive electrode slurry was stirred in a container and then allowed to stand for 7 days. The total volume of the positive electrode slurry was divided into three parts in the height direction. The densities of the top layer liquid and the bottom layer liquid were ρ U , ρ L (g / mL), 0.60≦ρ U / ρ L ≦1.00, and ρ U / ρ L The upper limit of may be 0.98 or less or 0.95 or less, and ρ U / ρ L The lower limit of the above ρ is more preferably 0.70 or more, even more preferably 0.80 or more, and even more preferably 0.85 or more. U / ρ L The upper and lower limits can be combined arbitrarily.

[0126] ρ U / ρ L If ρ is 0.60 or more, the alkali metal compound having a high density in the positive electrode slurry is less likely to settle, and the alkali metal compound is not unevenly distributed in the vicinity of the positive electrode current collector even during the formation of the coating film of the positive electrode precursor, and a non-aqueous hybrid capacitor having both high input / output characteristics and excellent high-temperature storage characteristics can be obtained. U / ρ L If the ratio is 1.00 or less, the solid content in the positive electrode slurry is sufficiently dispersed, the coating stability during the formation of the positive electrode precursor is excellent, and pre-doping of alkali metal ions into the negative electrode proceeds uniformly during the assembly of the nonaqueous hybrid capacitor. The ratio of the water-soluble polymer to the total mass of the carbon material contained in the slurry, the type of alkali metal compound, its average particle size, and its content relative to the total mass of all solids excluding the solvent, the type and oxidation resistance of the binder, the type of activated carbon, and the average particle size of the positive electrode active material may be the same as the ratio of the water-soluble polymer to the total mass of the carbon material contained in the positive electrode active material layer, the type of alkali metal compound, its average particle size, and its content relative to the total mass of all solids excluding the solvent, the type and oxidation resistance of the binder, the type of activated carbon, and the average particle size of the positive electrode active material described above.

[0127] [Total Amount of Acidic Functional Groups in Positive Electrode Precursor and Positive Electrode Slurry] In this embodiment, the positive electrode precursor is immersed in water for 24 hours, removed, and then a sodium hydroxide solution is added to the positive electrode active material layer. The total amount of acidic functional groups in the positive electrode active material layer is calculated by back titration using hydrochloric acid. The upper limit of the total amount of acidic functional groups in the positive electrode active material layer is preferably 1.50 mmol / g or less, more preferably 1.00 mmol / g or less, and particularly preferably 0.80 mmol / g or less. The lower limit is preferably 0.20 mmol / g or more, and even more preferably 0.25 mmol / g or more. The upper and lower limits of the total amount of acidic functional groups in the positive electrode active material layer can be arbitrarily combined.

[0128] In this embodiment, the positive electrode slurry is dried to remove the solvent, immersed in water for 24 hours, and then the solid is extracted. The solid is then added with a sodium hydroxide solution, and the total amount of acidic functional groups in the solid is calculated by back titration using hydrochloric acid. The upper limit of the total amount of acidic functional groups in the positive electrode slurry is preferably 1.50 mmol / g or less, more preferably 1.00 mmol / g or less, and particularly preferably 0.80 mmol / g or less. The lower limit is preferably 0.20 mmol / g or more, and even more preferably 0.25 mmol / g or more. The upper and lower limits of the total amount of acidic functional groups in the positive electrode slurry can be combined in any manner.

[0129] In this embodiment, it is important to control the state of the carbon material containing activated carbon, which is the positive electrode active material in the positive electrode slurry and the positive electrode precursor positive electrode active material layer. Specifically, as described above, carboxymethyl cellulose acts like a surfactant for the carbon material in the positive electrode active material layer and the positive electrode slurry, affecting the distribution of the carbon material in the positive electrode active material layer and the positive electrode slurry. When the positive electrode precursor is incorporated into a nonaqueous hybrid capacitor, the state of carboxymethyl cellulose adsorbed on the carbon material surface determines the performance of the nonaqueous hybrid capacitor.

[0130] In this embodiment, the total amount of acidic functional groups in the positive electrode active material layer obtained by immersing the positive electrode precursor in water for 24 hours and then removing the positive electrode slurry, and the total amount of acidic functional groups in the solid obtained by drying the positive electrode slurry to remove the solvent and then immersing the positive electrode precursor in water for 24 hours are defined as indicators of the state of carboxymethyl cellulose adsorbed on the carbon material surface. In this embodiment, the positive electrode precursor and positive electrode slurry contain alkali metal compounds. Therefore, even if sodium hydroxide solution is added directly to the positive electrode precursor and positive electrode slurry and then back titration is performed using hydrochloric acid, it is impossible to estimate the total amount of acidic functional groups in the positive electrode active material layer and positive electrode slurry due to the alkalinity of the alkali metal compounds. Therefore, by immersing the dried positive electrode precursor or the dried positive electrode slurry in water, the alkali metal compounds and water-soluble polymers in the positive electrode active material layer and the dried positive electrode slurry can be dissolved in water and removed from the solid material. However, some or all of the carboxymethyl cellulose physically adsorbed on the carbon material surface during the preparation of the positive electrode slurry for the positive electrode precursor remains in the solid material even when the positive electrode precursor is immersed in water. The total amount of acidic functional groups in the positive electrode active material layer obtained by immersing this positive electrode precursor in water for 24 hours and then removing it, and the total amount of acidic functional groups in the solid material obtained by drying the positive electrode slurry to remove the solvent and then immersing it in water for 24 hours and then removing it, are presumably values ​​obtained by subtracting the amount of surface functional groups removed by adsorption of carboxymethyl cellulose from the amount of surface functional groups in the carbon material itself, including activated carbon, in other words, reflect the state of carboxymethyl cellulose adsorbed on the surface of the carbon material.

[0131] If the total amount of acidic functional groups in the positive electrode active material layer obtained by immersing the positive electrode precursor in water for 24 hours and then extracting it is 0.15 mmol / g or more per weight of the positive electrode active material layer, or if the total amount of acidic functional groups in the solid material obtained by drying the positive electrode slurry to remove the solvent and then immersing it in water for 24 hours is 0.15 mmol / g or more per weight of the solid material, then when the positive electrode precursor is incorporated into a nonaqueous hybrid capacitor, the wettability of the carbon material containing activated carbon, which is the positive electrode active material, to the electrolyte is ensured, thereby shortening the electrolyte impregnation time, preventing excessive adsorption of carboxymethyl cellulose on the surface of the carbon material, and maintaining high input / output characteristics. On the other hand, if the total amount of acidic functional groups in the positive electrode active material layer obtained by immersing the positive electrode precursor in water for 24 hours and then extracting it is 2.00 mmol / g or less per weight of the positive electrode active material layer, or if the total amount of acidic functional groups in the solid obtained by drying the positive electrode slurry to remove the solvent and then immersing it in water for 24 hours and then extracting it is 2.00 mmol / g or less per weight of the solid, then when the positive electrode precursor is incorporated into a nonaqueous hybrid capacitor, it is possible to suppress the formation of a coating due to a side reaction during charging and discharging that is caused by the amount of functional groups in the carbon material itself, including activated carbon, which is the positive electrode active material, and it is also possible to suppress the aggregation of carbon material particles due to a lack of carboxymethyl cellulose on the surface of the carbon material, thereby suppressing an increase in resistance and a decrease in durability.

[0132] [Positive electrode precursor solvent soaking time] In this embodiment, the penetration time when 3 μL of a mixed solvent of ethylene carbonate:methyl ethyl carbonate = 33:67 (volume ratio) is dropped onto the positive electrode precursor is 5 seconds or more and 40 seconds or less. The upper limit of the penetration time is more preferably 35 seconds or less, and even more preferably 30 seconds or less, and the lower limit is more preferably 7.5 seconds or more, and even more preferably 10 seconds or more. The upper and lower limits of the penetration time can be combined as desired. The penetration time of the mixed solvent in the positive electrode precursor is a value measured after the above-described pressing. When pressing is performed multiple times, the value is measured after the final pressing. When an electrode laminate or an electrode wound body described below is produced without pressing, the value is measured in an unpressed state.

[0133] The permeation time of the mixed solvent in the positive electrode precursor is dependent on the electrode state and affects performance when incorporated into a nonaqueous hybrid capacitor. If the permeation time of the mixed solvent in the positive electrode precursor is 5 seconds or longer, there will not be excessive voids inside the electrode, and sufficient electrode strength can be ensured, resulting in high durability. On the other hand, if the permeation time of the mixed solvent in the positive electrode precursor is 40 seconds or less, the binder and water-soluble polymer will not segregate on the surface of the positive electrode precursor, but will be uniformly distributed within the positive electrode active material, thereby maintaining sufficient electrode strength and high input characteristics.

[0134] [Volume resistivity and interface resistance of positive electrode precursor] In this embodiment, the volume resistivity of the positive electrode active material layer of the positive electrode precursor is 1.0 Ω cm or more and 10.0 Ω cm or less, and the interface resistance between the positive electrode active material layer and the positive electrode current collector is 0.01 Ω cm 2 More than 1.00Ω cm 2 The upper limit of the volume resistivity of the positive electrode active material layer is more preferably 8.0 Ω·cm or less, and even more preferably 6.0 Ω·cm or less, and the lower limit is more preferably 1.2 Ω·cm or more, and even more preferably 1.4 Ω·cm or more. The upper and lower limits of the volume resistivity of the positive electrode active material layer can be arbitrarily combined. In addition, the upper limit of the interface resistance between the positive electrode active material layer and the positive electrode current collector is 0.80 Ω·cm. 2 Less than 0.60 Ω cm is preferable. 2 More preferably, the lower limit is 0.02 Ω cm. 2 More preferably, 0.03 Ω cm or more 2 The upper and lower limits of the interface resistance between the positive electrode active material layer and the positive electrode current collector can be combined arbitrarily. The volume resistivity of the positive electrode active material layer and the interfacial resistance between the positive electrode active material layer and the positive electrode current collector are values ​​measured after the above-mentioned pressing. When pressing is performed multiple times, the values ​​are measured after the final pressing. When an electrode laminate or an electrode wound body described below is produced without pressing, the values ​​are measured in an unpressed state. Furthermore, in the present embodiment, when a positive electrode active material layer is provided on both sides of the positive electrode current collector, it is sufficient that the volume resistivity of the positive electrode active material layer and the interface resistance between the positive electrode active material layer and the positive electrode current collector are within the above-mentioned ranges on at least one side of the positive electrode active material layer, and it is preferable that the volume resistivity of the positive electrode active material layer and the interface resistance between the positive electrode active material layer and the positive electrode current collector are within the above-mentioned ranges on both sides of the positive electrode active material layer.

[0135] The volume resistivity of the positive electrode active material layer of the positive electrode precursor and the interface resistance between the positive electrode active material layer and the positive electrode current collector affect the performance when incorporated into a non-aqueous hybrid capacitor. If the volume resistivity of the positive electrode active material layer is 1.0 Ω·cm or higher, the positive electrode active material layer is overfilled, maintaining a moderate amount of void space, which does not hinder ion movement during charge and discharge, and the alkali metal compounds during pre-doping are uniformly oxidized and decomposed, thereby maintaining high durability.On the other hand, if the volume resistivity of the positive electrode active material layer is 10.0 Ω·cm or lower, the conductive network within the positive electrode active material layer is sufficiently secured, promoting the oxidative decomposition of the alkali metal compounds during pre-doping, resulting in high durability and excellent input / output characteristics. In addition, the interface resistance between the positive electrode active material layer and the positive electrode current collector is 0.01 Ω cm 2 If the interfacial resistance between the positive electrode active material layer and the positive electrode current collector is 1.00 Ω cm or more, the binder in the positive electrode active material is not distributed unevenly on the surface of the positive electrode active material, and sufficient electrode strength can be ensured, thereby maintaining high durability. 2 If the above ratio is less than 1, the binder in the positive electrode active material and resistors such as water-soluble polymers are not distributed excessively unevenly at the interface between the positive electrode active material layer and the positive electrode current collector, the alkali metal compound is oxidized and decomposed uniformly during pre-doping, and the charge / discharge reaction also proceeds uniformly, thereby maintaining high input / output characteristics and high durability.

[0136] [Peel strength of positive electrode precursor] In this embodiment, the peel strength of the positive electrode active material layer of the positive electrode precursor is 0.02 N / cm or more and 3.00 N / cm or less. The upper limit of the peel strength of the positive electrode active material layer is more preferably 2.76 N / cm or less, and even more preferably 1.64 N / cm or less, and the lower limit is more preferably 0.03 N / cm or more, and even more preferably 0.05 N / cm or more. The upper and lower limits of the peel strength of the positive electrode active material layer can be combined in any manner. The peel strength of the positive electrode active material layer of the positive electrode precursor is a value measured after the above-described pressing. When pressing is performed multiple times, the peel strength is a value measured after the final pressing. When an electrode laminate or an electrode wound body described below is produced without pressing, the peel strength is a value measured in an unpressed state.

[0137] If the peel strength of the positive electrode active material layer is 0.02 N / cm or more, when the positive electrode active material layer is incorporated into a nonaqueous hybrid capacitor, chipping of the positive electrode active material layer due to gas generation during pre-doping can be suppressed, micro-short circuits can be suppressed, leading to a reduction in the defective rate during manufacturing and excellent durability. On the other hand, if the peel strength of the positive electrode active material layer is 3.00 N / cm or less, the binder and water-soluble polymer are not present in excess throughout the positive electrode active material layer, or are not excessively and unevenly distributed at the interface between the positive electrode active material layer and the positive electrode current collector, thereby maintaining high input / output characteristics.

[0138] [Other properties of the cathode precursor] The thickness of the positive electrode active material layer is preferably 20 μm to 200 μm, more preferably 25 μm to 100 μm, and even more preferably 30 μm to 80 μm per side of the positive electrode current collector. A positive electrode active material layer having a thickness of 20 μm or more can exhibit sufficient charge / discharge capacity. A positive electrode active material layer having a thickness of 200 μm or less can maintain low ion diffusion resistance within the electrode. Therefore, sufficient input / output characteristics can be obtained, and the cell volume can be reduced, thereby increasing the energy density. The upper and lower limits of the thickness range of the positive electrode active material layer can be arbitrarily combined. In this specification, when the current collector has through-holes or irregularities, the thickness of the positive electrode active material layer refers to the average thickness per side of the current collector in the portion not having through-holes or irregularities.

[0139] <Negative electrode> The negative electrode generally has a negative electrode current collector and a negative electrode active material layer present on one or both sides of the negative electrode current collector.

[0140] [Negative electrode active material layer] The negative electrode active material layer preferably contains a negative electrode active material capable of absorbing and releasing alkali metal ions. In addition to the negative electrode active material, the negative electrode active material layer may contain optional components such as a conductive filler, a binder, and a dispersion stabilizer, as necessary.

[0141] -Negative electrode active material- The negative electrode active material can be a material capable of absorbing and releasing alkali metal ions. Specific examples of the negative electrode active material include carbon materials, titanium oxides, silicon, silicon oxides, silicon alloys, silicon compounds, tin, and tin compounds. The content of the carbon material relative to the total mass of the negative electrode active material is preferably 50% by mass or more, more preferably 70% by mass or more, or even 100% by mass. From the viewpoint of obtaining the effects of the combined use of other materials, the content of the carbon material is preferably, for example, 90% by mass or less, and may be 80% by mass or less. The upper and lower limits of the range of the content of the carbon material can be arbitrarily combined.

[0142] Examples of the carbon material include non-graphitizable carbon materials, graphitizable carbon materials, carbon black, carbon nanoparticles, activated carbon, artificial graphite, natural graphite, graphitized mesophase carbon microspheres, graphite whiskers, amorphous carbonaceous materials such as polyacene-based substances, carbonaceous materials obtained by heat-treating carbonaceous material precursors, pyrolysis products of furfuryl alcohol resins or novolac resins, fullerenes, carbon nanophones, and composite carbon materials thereof. The carbonaceous material precursor is not particularly limited as long as it can be converted into a carbonaceous material by heat treatment, and examples include petroleum-based pitch, coal-based pitch, mesocarbon microbeads, coke, and synthetic resins (e.g., phenolic resins).

[0143] -Optional components of the negative electrode active material layer- The negative electrode active material layer may contain optional components such as a conductive filler, a binder, and a dispersion stabilizer in addition to the negative electrode active material, as required.

[0144] The type of conductive filler is not particularly limited, and examples thereof include acetylene black, ketjen black, vapor-grown carbon fiber, etc. The amount of the conductive filler used is preferably more than 0 part by mass and not more than 30 parts by mass, more preferably 0.01 part by mass or more and 20 parts by mass or less, and even more preferably 0.1 part by mass or more and 15 parts by mass or less, relative to 100 parts by mass of the negative electrode active material.

[0145] The binder is not particularly limited, and examples thereof include PVdF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), polyimide, latex, styrene-butadiene copolymer, fluororubber, and acrylic copolymer. The amount of binder used is preferably 1 part by mass or more and 30 parts by mass or less, more preferably 2 parts by mass or more and 27 parts by mass or less, and even more preferably 3 parts by mass or more and 25 parts by mass or less, relative to 100 parts by mass of the negative electrode active material. When the amount of binder used is 1 part by mass or more, sufficient electrode strength is achieved. On the other hand, when the amount of binder used is 30 parts by mass or less, the ingress and egress of alkali metal ions into and from the negative electrode active material is not inhibited, and high input / output characteristics are achieved.

[0146] The dispersion stabilizer is not particularly limited, and examples thereof include PVP (polyvinylpyrrolidone), PVA (polyvinyl alcohol), and cellulose derivatives. The amount of the dispersion stabilizer used is preferably more than 0 part by mass, or 0.1 part by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the negative electrode active material. When the amount of the dispersion stabilizer used is 10 parts by mass or less, the ingress and egress of alkali metal ions into and from the negative electrode active material is not inhibited, and high input / output characteristics are exhibited.

[0147] [Negative electrode current collector] The material constituting the negative electrode current collector is preferably a metal foil that has high electronic conductivity and is resistant to degradation due to elution in the electrolytic solution and reaction with the electrolyte or ions. Such metal foil is not particularly limited, and examples thereof include aluminum foil, copper foil, nickel foil, and stainless steel foil. Copper foil is preferred as the negative electrode current collector in a nonaqueous hybrid capacitor.

[0148] The metal foil may be a metal foil without irregularities or through holes, or may be a metal foil with irregularities that have been subjected to embossing, chemical etching, electrolytic deposition, blasting, or the like, or may be a metal foil with through holes such as expanded metal, punched metal, or etched foil. Among these, metal foil without through holes is preferred for the negative electrode current collector, as it is cheaper to manufacture, easier to make a thin film, which contributes to a high energy density, and lowers current collection resistance, resulting in high input / output characteristics.

[0149] The thickness of the negative electrode current collector is not particularly limited as long as it can sufficiently maintain the shape and strength of the negative electrode, but is preferably, for example, 1 to 100 μm.

[0150] [Manufacturing of negative electrodes] The negative electrode comprises a negative electrode active material layer on one or both sides of a negative electrode current collector. In a typical embodiment, the negative electrode active material layer is adhered to the negative electrode current collector.

[0151] The negative electrode can be manufactured by known electrode manufacturing techniques for lithium ion batteries, electric double layer capacitors, etc. For example, various materials including the negative electrode active material are dispersed or dissolved in water or an organic solvent to prepare a slurry-like coating liquid, and this coating liquid is applied to one or both sides of a negative electrode current collector to form a coating film, which is then dried to obtain a negative electrode. The obtained negative electrode may then be pressed to adjust the film thickness and bulk density of the negative electrode active material layer.

[0152] The thickness of the negative electrode active material layer is preferably 5 μm or more and 100 μm or less per side. If the thickness is 5 μm or more, no streaks or the like occur when the negative electrode active material layer is applied, resulting in excellent coatability. If the thickness is 100 μm or less, high energy density can be achieved by reducing the cell volume. The upper and lower limits of the thickness range of the negative electrode active material layer can be arbitrarily combined. When the current collector has through-holes or irregularities, the thickness of the negative electrode active material layer refers to the average thickness per side of the current collector in the portion that does not have through-holes or irregularities.

[0153] The bulk density of the negative electrode active material layer is preferably 0.30 g / cm 3 More than 1.8g / cm 3 Bulk density is 0.30 g / cm or less. 3 If the bulk density is 1.8 g / cm or more, sufficient strength can be maintained and sufficient conductivity between the negative electrode active materials can be exhibited. 3 If the content is equal to or less than this, pores that allow ions to diffuse sufficiently can be secured in the negative electrode active material layer.

[0154] <Separator> The positive electrode precursor and the negative electrode can be stacked with a separator interposed therebetween, or stacked and wound, to form an electrode stack or electrode wound body having the positive electrode precursor, separator, and negative electrode.

[0155] The separator may be a polyethylene microporous membrane or a polypropylene microporous membrane used in lithium ion secondary batteries, or a cellulose nonwoven paper used in electric double layer capacitors. A membrane composed of organic or inorganic fine particles may be laminated on one or both sides of the separator. The separator may contain organic or inorganic fine particles.

[0156] The thickness of the separator is preferably 5 μm or more and 35 μm or less. A thickness of 5 μm or more is preferred because it tends to reduce self-discharge due to internal micro-short circuits. A thickness of 35 μm or less is preferred because it tends to improve the input / output characteristics of the energy storage element.

[0157] The thickness of the film composed 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 preferred because it tends to reduce self-discharge due to internal micro-short circuits. A thickness of 10 μm or less is preferred because it tends to improve the input / output characteristics of the energy storage element.

[0158] <Exterior body> As the exterior body, a metal can, a laminate film, etc. can be used. As the metal can, one made of aluminum is preferred. As the laminate film, a film in which a metal foil and a resin film are laminated is preferred, and an example is a three-layer structure consisting of an outer layer resin film / metal foil / inner layer resin film. The outer layer resin film is intended to prevent damage to the metal foil due to contact, etc., and resins such as nylon or polyester can be suitably used. The metal foil is intended to prevent permeation of moisture and gas, and foils of copper, aluminum, stainless steel, etc. can be suitably used. The inner layer resin film is intended to protect the metal foil from the electrolyte solution stored inside and to melt-seal the exterior body when it is heat-sealed, and polyolefins, acid-modified polyolefins, etc. can be suitably used.

[0159] <Non-aqueous electrolyte> The electrolyte used in the nonaqueous hybrid capacitor is preferably a nonaqueous electrolyte. That is, the electrolyte contains a nonaqueous solvent. The nonaqueous electrolyte contains 0.5 mol / L or more of an alkali metal salt based on the total amount of the nonaqueous electrolyte. That is, the nonaqueous electrolyte contains an alkali metal salt as an electrolyte. Examples of nonaqueous solvents contained in the nonaqueous electrolyte include cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0160] <<Method for manufacturing a non-aqueous hybrid capacitor>> <Assembly> Typically, a positive electrode precursor and a negative electrode cut into sheets are stacked with a separator interposed therebetween to obtain an electrode laminate, and a positive electrode terminal and a negative electrode terminal are connected to the electrode laminate. Alternatively, a positive electrode precursor and a negative electrode are stacked with a separator interposed therebetween and wound to obtain an electrode wound body, and a positive electrode terminal and a negative electrode terminal are connected to the electrode wound body. The shape of the electrode wound body may be cylindrical or flat.

[0161] The method for connecting the positive electrode terminal and the negative electrode terminal is not particularly limited, and methods such as resistance welding and ultrasonic welding can be used.

[0162] The electrode laminate or electrode wound body to which the terminals are connected is preferably dried to remove the remaining solvent. The drying method is not limited, and drying can be performed by vacuum drying or the like. The remaining solvent is preferably 1.5 mass % or less per weight of the positive electrode active material layer or the negative electrode active material layer. Residual solvent exceeding 1.5 mass % is undesirable because the solvent remains in the system and deteriorates the self-discharge characteristics.

[0163] The dried electrode laminate or electrode wound body is preferably housed in an exterior body, such as a metal can or a laminate film, in a dry environment, preferably with a dew point of -40°C or lower, and sealed with only one opening remaining. If the dew point is higher than -40°C, moisture may adhere to the electrode laminate or electrode wound body, leaving water in the system and deteriorating the self-discharge characteristics. The method for sealing the exterior body is not particularly limited, and methods such as heat sealing and impulse sealing may be used.

[0164] <Injection, impregnation, sealing> After assembly, a non-aqueous electrolyte solution is injected into the electrode stack or electrode wound body housed in the outer casing. After the injection, it is desirable to thoroughly impregnate the positive electrode precursor, negative electrode, and separator with the non-aqueous electrolyte solution. If the electrolyte solution is not immersed in at least a portion of the positive electrode precursor, negative electrode, and separator, the doping process will proceed unevenly in the pre-doping step described below, resulting in increased resistance and reduced durability of the resulting non-aqueous hybrid capacitor. The impregnation method is not particularly limited. For example, a method can be used in which the non-aqueous hybrid capacitor after the injection is placed in a decompression chamber with the outer casing open, the chamber is decompressed using a vacuum pump, and the pressure is returned to atmospheric pressure. After the impregnation, the non-aqueous hybrid capacitor with the outer casing open is sealed while decompressing.

[0165] <Pre-Dope> A preferred pre-doping method is to apply a voltage between the positive electrode precursor and the negative electrode, decompose the alkali metal compound in the positive electrode precursor to release alkali metal ions, and reduce the alkali metal ions at the negative electrode, thereby pre-doping the alkali metal ions into the negative electrode active material layer.

[0166] During pre-doping, gases such as CO2 are generated due to the oxidative decomposition of the alkali metal compound in the positive electrode precursor. Therefore, when applying a voltage, it is preferable to take measures to release the generated gas to the outside of the exterior body. Examples of such measures include a method of applying a voltage with a part of the exterior body open; a method of applying a voltage with an appropriate gas release means, such as a gas vent valve or a gas permeable film, previously installed in a part of the exterior body; etc.

[0167] <Aging> After the pre-doping step, the non-aqueous hybrid capacitor is preferably subjected to aging, during which the solvent in the electrolyte decomposes at the negative electrode, forming an alkali metal ion-permeable solid polymer coating on the negative electrode surface.

[0168] The aging method is not particularly limited, but for example, a method of reacting the solvent in the electrolyte in a high-temperature environment can be used.

[0169] <Gas release> After aging, it is preferable to further degas the capacitor to completely remove any remaining gas from the electrolyte, the positive electrode, and the negative electrode. If gas remains in at least part of the electrolyte, the positive electrode, and the negative electrode, ion conduction is inhibited, resulting in an increase in the resistance of the resulting nonaqueous hybrid capacitor.

[0170] The method for degassing is not particularly limited, and for example, a method can be used in which the nonaqueous hybrid capacitor is placed in a reduced pressure chamber with the outer casing open, and the chamber is reduced pressure using a vacuum pump.

[0171] <Characteristics evaluation of energy storage elements> (capacitance) In this specification, the capacitance F(F) is a value obtained by the following method. First, a cell corresponding to the nonaqueous hybrid capacitor is charged at a constant current of 2 C in a thermostatic chamber set at 25°C until it reaches 3.8 V, and then a constant voltage charge of 3.8 V is applied for a total of 30 minutes. After that, the capacity when a constant current discharge is performed at a current of 2 C to 2.2 V is defined as Q. Using the Q obtained here, F is the value calculated by the formula F = Q / (3.8 - 2.2).

[0172] Here, the C-rate of current refers to the current value at which constant current discharge from the upper limit voltage to the lower limit voltage is completed in one hour. In this specification, 1 C refers to the current value at which constant current discharge from the upper limit voltage of 3.8 V to the lower limit voltage of 2.2 V is completed in one hour.

[0173] (internal resistance) In this specification, the internal resistance Ra (Ω) is a value obtained by the following method. First, the nonaqueous hybrid capacitor was charged at a constant current of 20 C in a thermostatic chamber set at 25°C until it reached 3.8 V, and then a constant voltage of 3.8 V was applied for a total of 30 minutes for constant voltage charging. Subsequently, a constant current discharge was performed at a current of 20 C down to 2.2 V to obtain a discharge curve (time-voltage). In this discharge curve, the voltage at 0 seconds, obtained by linear approximation from the voltage values ​​at 2 and 4 seconds of discharge, was defined as Vo. The voltage drop ΔV was calculated as 3.8 - Vo, and Ra was calculated as ΔV / (current value at 20 C).

[0174] (Electric energy) In this specification, the amount of electric energy E (Wh) is a value obtained by the following method. Using the capacitance F(F) calculated using the method described above, F×(3.8 2 -2.2 2 ) / 2 / 3600.

[0175] (volume) The volume V(L) of the energy storage element refers to the volume of the portion of the electrode laminate or electrode wound body where the positive electrode active material layer and the negative electrode active material layer are stacked and enclosed by the exterior body.

[0176] For example, in the case of an electrode stack or electrode wound body housed in a laminate film, the region of the electrode stack or electrode wound body where the positive electrode active material layer and the negative electrode active material layer exist is housed in a cup-shaped laminate film, and the volume (V x ) is the outer length of this cup forming part (l x ) and outer width (w x ), and the thickness of the energy storage element including the laminate film (t x ) by V x =l x ×w x ×t x It is calculated as follows.

[0177] In the case of an electrode stack or an electrode wound body housed in a rectangular metal can, the volume of the energy storage element is simply the volume of the outer dimensions of the metal can. y ) is the outer length of a rectangular metal can (l y ) and outer width (w y ), outer thickness (t y ) by V y =l y ×w y ×t y It is calculated as follows.

[0178] Even in the case of an electrode wound body housed in a cylindrical metal can, the volume of the energy storage element is the volume of the outer dimensions of the metal can. z ) is the outer radius (r) and outer length (l) of the bottom or top surface of a cylindrical metal can. z ) by V z =3.14×r×r×l z It is calculated as follows.

[0179] (High temperature storage test) In this specification, the amount of gas generated during a high-temperature storage test and the rate of increase in internal resistance at room temperature after a high-temperature storage test are measured by the following method: First, a cell corresponding to the nonaqueous hybrid capacitor was charged at a constant current of 100°C in a thermostatic chamber set at 25°C until it reached 4.0 V. This was followed by a 10-minute constant-voltage charge at 4.0 V. The cell was then stored in a 60°C environment, removed from the 60°C environment every two weeks, and charged to 4.0 V using the aforementioned charging process. The cell was then stored again in a 60°C environment. This process was repeated, and the cell volume Va before storage and the cell volume Vb after three months of storage were measured using the Archimedes method. Vb-Va was defined as the amount of gas generated during three months of storage at a cell voltage of 4.0 V and an ambient temperature of 60°C. When the resistance value obtained for the cell after the high-temperature storage test using the same measurement method as for the room-temperature internal resistance is defined as the room-temperature internal resistance Rb after the high-temperature storage test, the rate of increase in the room-temperature internal resistance after the high-temperature storage test relative to the room-temperature internal resistance Ra before the start of the high-temperature storage test is calculated as Rb / Ra.

[0180] "Measurement Method" <BET Specific Surface Area, Mesopore Volume, Micropore Volume, Average Pore Diameter> The BET specific surface area, mesopore volume, micropore volume, and average pore diameter in this embodiment are values obtained by the following methods respectively. The sample is vacuum dried at 200 °C for one day and night, and nitrogen is used as the adsorbate to measure the adsorption / desorption isotherm. Using the adsorption-side isotherm obtained here, the BET specific surface area is calculated by the BET multi-point method or the BET one-point method, the mesopore volume is calculated by the BJH method, and the micropore volume is calculated by the MP method respectively.

[0181] The BJH method is a calculation method generally used for the analysis of mesopores, and was proposed by Barrett, Joyner, Halenda et al. (E. P. Barrett, L. G. Joyner and P. Halenda, J. Am. Chem. Soc., 73, 373(1951)).

[0182] The MP method means a method for obtaining the micropore volume, micropore area, and micropore distribution by using the "t-plot method" (B.C. Lippens, J.H. de Boer, J. Catalysis, 4319(1965)), and is a method devised by R.S. Mikhail, Brunauer, and Bodor (R.S. Mikhail, S. Brunauer, E.E. Bodor, J. Colloid Interface Sci., 26, 45 (1968)).

[0183] The average pore diameter refers to the value obtained by dividing the total pore volume per unit mass of the sample by the above BET specific surface area, which is obtained by measuring the equilibrium adsorption amount of nitrogen gas at each relative pressure under liquid nitrogen temperature.

[0184] <Viscosity Ratio of Different Shear Rates> The viscosity ratios η2 / η1, η3 / η2, and η4 / η3 of different shear rates in this embodiment are values obtained by the following methods respectively. First, using a rheometer, at a temperature of 25 °C and a shear rate of 5 s-1 , 50s -1 , 500s -1 , and 2000s -1 After measuring for 30 seconds or more under each condition, obtain the stable viscosities η1, η2, η3, and η4. Using the viscosity values ​​obtained above, calculate the viscosity ratios η2 / η1, η3 / η2, and η4 / η3 at different shear rates. -1 From the 50s -1 To the 50s -1 From the 500s -1 To the 500s -1 From the 2000s -1 When increasing the shear rate to each of the above ranges, the increase may be made in one step, or the shear rate may be increased in multiple steps within the above range, while appropriately obtaining the viscosity at each shear rate.

[0185] <Viscosity and TI value> The viscosity (ηb) and TI value in this embodiment are values ​​that are determined by the following method. First, an E-type viscometer is used to measure the viscosity at a temperature of 25°C and a shear rate of 2 s -1 Obtain a stable viscosity (ηa) after measuring for 2 minutes or more under the conditions. -1 The viscosity (ηb) is measured under the same conditions as above, except that the shear rate is changed to . Using the viscosity value obtained above, the TI value is calculated using the formula TI value = ηa / ηb. -1 From the 20s -1 When increasing the shear rate, the increase may be made in one step, or the shear rate may be increased in multiple steps within the above range while appropriately obtaining the viscosity at each shear rate.

[0186] <Viscosity ratio and density ratio of the top layer liquid and the bottom layer liquid> The viscosity ratio η of the top layer liquid and the bottom layer liquid in this embodiment U / η L and density ratio ρ U / ρ L are values ​​determined by the following methods. U , η L , ρ U , and ρ LThe viscosity, density, and density of the top layer liquid are measured when the total volume of the positive electrode slurry is divided into three parts in the height direction after being stirred in a container and left to stand for 7 days. To prepare a slurry sample for measurement, first fill a container with the slurry sample. The container used for measurement is not particularly limited in volume or shape, as long as it can uniformly stir the slurry, can be left standing stably, and can divide the total volume of the slurry into three portions without mixing. For example, the volume of the container is preferably 50 mL to 100 L, and the shape of the container is preferably approximately cylindrical, more preferably cylindrical. Furthermore, the amount of slurry filled into the container is preferably 50 vol % to 90 vol % of the total volume of the container. Next, the slurry sample filled in the container is stirred using a stirrer in an environment of 25°C so that the constituent materials in the slurry are uniformly dispersed. At this time, the stirring method is not particularly limited as long as the constituent materials in the slurry can be stirred uniformly without settling. For example, a stirrer with the product name "Awatori Rentaro" manufactured by Thinky Corporation is used as the stirrer, and stirring is performed at a rotation speed of 1000 rpm for 2 minutes. After stirring, the slurry sample is left to stand in an environment of 25°C for 7 days. After standing, the total volume of the slurry sample is divided into three parts in the height direction, and the top layer liquid, middle layer liquid, and bottom layer liquid are separated. At this time, the division method is not particularly limited as long as the liquids in each divided layer can be separated without substantially mixing. The obtained top and bottom layers were measured using an E-type viscometer at a temperature of 25°C and a shear rate of 20 s -1 The stable viscosity after measuring for 2 minutes or more under the conditions is η U and η L Let's say.

[0187] The densities of the obtained top and bottom liquid layers are determined by the density measurement method using a pycnometer specified in JIS Z8804. That is, the pycnometer is filled with a standard substance such as water, and the internal volume of the pycnometer is first calibrated by measuring the mass B1 [g] of the empty pycnometer at room temperature (temperature t°C) and the mass B2 [g] of the pycnometer containing the standard substance. Next, the pycnometer is filled with the sample liquid, and the mass B3 [g] of the pycnometer containing the sample liquid at room temperature (temperature t°C) is measured. At this time, it is preferable to degas the sample liquid in the pycnometer by reducing the pressure or vibrating it to prevent bubbles from entering the liquid. The density ρ of the sample liquid at temperature t°C is t [g / mL] can be calculated using the following formula (1). ρ t =(B3-B1) / (B2-B1)×(ρ s -ρ air )+ρ air Formula (1) {where ρ s ; density of the standard substance at temperature t°C [g / mL], ρ air ;The density of air in the measurement environment is [g / mL].} The obtained top layer liquid and bottom layer liquid were used as sample liquids and measured by the above-mentioned density measurement method, respectively. U and ρ L is required.

[0188] <Weight ratio of all solid components in the slurry excluding the solvent> The weight ratio W of all solid components excluding the solvent in the slurry in this embodiment TThe method for measuring is not particularly limited, but can be measured, for example, by the following method. First, a slurry sample is prepared, and the total mass W1 [g] of the sample is measured. Next, the slurry sample is dried, the solvent is volatilized to obtain only the solid components, and the mass W2 [g] of all solid components excluding the solvent is measured. The drying method and conditions are not particularly limited, but multi-stage drying is performed by combining atmospheric drying and vacuum drying, etc., at a drying temperature in the range of 60 to 200°C, preferably under conditions such that the amount of residual solvent is 1% by mass or less, more preferably 0.5% by mass or less. The amount of residual solvent can be quantified using GC / MS (gas chromatography mass spectrometry) when the solvent is an organic solvent medium, or using the Karl Fischer method when the solvent is an aqueous medium. Using the above method, the weight ratio W of all solid components excluding the solvent in the slurry can be calculated using the following formula (2): T can be calculated. W T =W2 / W1×100 Equation (2)

[0189] <Slurry pH> The pH in this embodiment is a value determined by the pH measurement method specified in JIS Z8802. That is, a sufficient amount of sample solution is taken so that the measured value does not change, the pH meter is calibrated, the pH meter electrodes are cleaned, and the pH of the sample solution is immediately measured and the measured value is read. The temperature of the sample solution is 25°C.

[0190] <Dispersion> The degree of dispersion in this embodiment is a value determined by a dispersion evaluation test using a particle gauge as specified in JIS K5600. That is, a sufficient amount of sample is poured into the deep end of a particle gauge having a groove of the desired depth according to the particle size, allowing it to slightly overflow from the groove. The long side of the scraper is parallel to the width direction of the gauge, and the cutting edge is placed so that it contacts the deep end of the groove of the particle gauge. While holding the scraper so that it is on the surface of the gauge, the surface of the gauge is pulled at a uniform speed perpendicular to the long side direction of the groove to a depth of 0 over 1 to 2 seconds, and within 3 seconds after the pull is completed, light is applied at an angle of 20° to 30° and observed, and the depth at which the particles appear in the groove of the particle gauge is read.

[0191] <Method for identifying alkali metal compounds> The method for identifying the alkali metal compounds contained in the positive electrode slurry or positive electrode precursor is not particularly limited, and for example, in the case of a positive electrode slurry, the alkali metal compounds can be identified in the state of a positive electrode precursor formed as a coating on a positive electrode current collector, or in the case of a positive electrode precursor in its original state, by SEM-EDX, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) as described below. The alkali metal compounds are preferably identified by a combination of the following analytical techniques.

[0192] In ion chromatography, anions can be identified by analyzing the water obtained after washing the positive electrode precursor with distilled water.

[0193] If the alkali metal compounds cannot be identified using the above analytical methods, other analytical methods are available: 7 Alkali metal compounds can also be identified using Li-solid-state NMR, XRD (X-ray diffraction), TOF-SIMS (time-of-flight secondary ion mass spectrometry), AES (Auger electron spectroscopy), TPD / MS (thermal evolved gas mass spectrometry), DSC (differential scanning calorimetry), etc.

[0194] (SEM-EDX) Alkali metal compounds and positive electrode active materials can be identified by oxygen mapping of SEM-EDX images of the positive electrode precursor surface measured at magnifications of 1000x to 4000x. For example, SEM-EDX images can be measured at an acceleration voltage of 10 kV, an emission current of 1 μA, a measurement pixel count of 256 × 256 pixels, and 50 integration times. To prevent sample charging, surface treatment with gold, platinum, osmium, or the like can be performed using methods such as vacuum deposition or sputtering. The measurement conditions for SEM-EDX images are preferably adjusted for brightness and contrast so that no pixels reach maximum brightness and the average brightness falls within the range of 40% to 60%. Particles containing bright areas binarized based on the average brightness value in the obtained oxygen mapping, with an area of ​​50% or more, are considered alkali metal compounds.

[0195] (Raman) The alkali metal compound and positive electrode active material composed of carbonate ions can be identified by Raman imaging of carbonate ions on the surface of the positive electrode precursor, measured at a magnification of 1000x to 4000x. Measurement conditions include an excitation light of 532 nm, an excitation light intensity of 1%, a long working distance of the objective lens of 50x, a diffraction grating of 1800 gr / mm, a point scanning mapping method (slit 65 mm, binning 5 pix), 1 mm steps, an exposure time of 3 seconds per point, one integration, and a noise filter. The measured Raman spectrum shows peaks from 1071 to 1104 cm. -1 A linear baseline is set within the range, and the area is calculated assuming that positive values ​​from the baseline are carbonate ion peaks, and the frequency is integrated. At this time, the frequency for the carbonate ion peak area, which is obtained by approximating noise components with a Gaussian function, is subtracted from the carbonate ion frequency distribution.

[0196] (XPS) By analyzing the electronic state of the positive electrode precursor by XPS, it is possible to determine the bonding state of the compounds contained in the positive electrode precursor.

[0197] As an example of measurement conditions, measurements can be made under the following conditions: X-ray source is monochromated AlKα, X-ray beam diameter is 100 μmφ (25 W, 15 kV), pass energy is narrow scan: 58.70 eV, charge neutralization is enabled, number of sweeps is narrow scan: 10 times (carbon, oxygen), 20 times (fluorine), 30 times (phosphorus), 40 times (alkali metal), 50 times (silicon), and energy step is narrow scan: 0.25 eV.

[0198] Before XPS measurement, the surface of the positive electrode precursor is preferably cleaned by sputtering. For example, the sputtering conditions are an acceleration voltage of 1.0 kV, a range of 2 mm × 2 mm, and a time of 1 minute (1.25 nm / min in terms of SiO).

[0199] Regarding the obtained XPS spectrum, The peak of Li1s binding energy 50-54 eV corresponds to LiO2 or Li-C bond, The peaks at 55-60 eV are LiF, Li2CO3, Li x PO y F z (wherein x, y, and z are integers of 1 to 6), The C1s peak at 285 eV is a C-C bond. The peak at 286 eV is the CO bond. The peak at 288 eV is COO, The peak at 290-292 eV is CO3 2- , CF bond, The O1s binding energy peak of 527-530 eV is 2- (Li2O), The peaks at 531-532 eV are CO, CO3, OH, and PO x (wherein x is an integer of 1 to 4), SiO x (wherein x is an integer of 1 to 4), The 533 eV peak is CO and SiO x (wherein x is an integer of 1 to 4), The F1s binding energy peak of 685 eV is LiF, The 687 eV peak is a C—F bond, and Li x PO y F z (wherein x, y, and z are integers from 1 to 6), PF6 - , Furthermore, the binding energy of P2p is The 133 eV peak is PO x (wherein x is an integer of 1 to 4), The peak at 134 to 136 eV is PF x (wherein x is an integer of 1 to 6), The peak of Si2p binding energy 99 eV is Si, silicide, The peaks at 101 to 107 eV are Si x O y (wherein x and y are any integers) It can be attributed as:

[0200] When the peaks of the obtained spectrum overlap, it is preferable to separate the peaks by assuming a Gaussian function or a Lorentzian function and assign the spectrum. The alkali metal compounds present can be identified from the results of the measurement of the electronic state and the results of the ratio of the elements present obtained above.

[0201] (Ion Chromatography) The anion species eluted in the water can be identified by analyzing the distilled water wash solution of the positive electrode precursor using ion chromatography. Columns can be ion exchange, ion exclusion, or reversed-phase ion pair. Detectors such as electrical conductivity detectors, UV-visible absorbance detectors, and electrochemical detectors can be used. Suppressor-based detectors, which use a suppressor before the detector, or non-suppressor-based detectors, which use a low-conductivity solution as the eluent without a suppressor, can be used. Measurements can also be performed in combination with a mass spectrometer or charged aerosol detectors.

[0202] Once the conditions, such as the column and eluent, are determined, the sample retention time is constant for each ionic species, and the magnitude of the peak response differs for each ionic species but is proportional to the concentration. Qualitative and quantitative determination of ionic species is possible by measuring standard solutions of known concentrations with traceability in advance.

[0203] <Method for quantifying alkali metal compounds in positive electrode slurry> The method for quantifying the alkali metal compounds contained in the positive electrode slurry is described below. In this embodiment, the weight ratio W of the alkali metal compounds in the slurry is A is based on the total mass of all solid components excluding the solvent. A The following water immersion method or combustion method is used to calculate the water immersion content, and the water immersion method and / or combustion method can be selected depending on the properties of the materials other than the alkali metal compound contained in the solid component, and a combination of the water immersion method and the combustion method may be used. For example, if the binder and / or the water-soluble polymer is water-insoluble, it is preferable to use the water immersion method, and if it is water-soluble, it is preferable to use the combustion method.

[0204] (Water immersion method) The solid component of the positive electrode slurry is immersed in distilled water, and the amount of alkali metal compounds can be quantified based on the weight change before and after immersion. T Similarly to the measurement method of (1), the slurry sample is dried, the solvent is evaporated to obtain only the solid components, and the mass W2 [g] of all solid components excluding the solvent is measured. Next, the solid components are thoroughly immersed in distilled water in an amount 100 times (100W2 [g]) the weight of the positive electrode slurry solid components for at least three days at 25°C to dissolve the alkali metal compounds into the water. At this time, it is preferable to take measures such as covering the container to prevent the distilled water from volatilizing. After immersion for at least three days, the solid components are removed from the distilled water and vacuum dried. Vacuum drying conditions are preferably, for example, a temperature of 100 to 200°C, a pressure of 0 to 10 kPa, and a time of 5 to 20 hours, under which the residual moisture content in the solid components is 1% by mass or less. The residual moisture content can be quantified using the Karl Fischer method. The weight of the solid components after vacuum drying is defined as W3 [g], and the weight ratio W of the alkali metal compounds contained in the positive electrode slurry solid components is calculated. A [% by mass] can be calculated using the following formula (3). W A =(W2-W3) / W2×100 Equation (3)

[0205] (Combustion method) The solid components of the positive electrode slurry are burned, and the amount of alkali metal compounds can be quantified based on the change in weight before and after the combustion. T As in the measurement method of (1), the slurry sample is dried and the solvent is evaporated to obtain only the solid component. Next, this solid component is placed in a platinum sample pan, and a TG curve is obtained using a TG measurement device under the following conditions. Gas: atmospheric air or compressed air Heating rate: 0.5℃ / min or less Temperature range: 25°C to 500°C or higher, up to 50°C below the melting point of alkali metal compounds The mass of the obtained TG curve at 25°C is defined as W2 [g] (mass of all solid components excluding solvent), and the mass at the first temperature above 500°C at which the mass loss rate becomes W2 × 0.01 [g / min] or less is defined as W4 [g]. Components other than alkali metal compounds, such as activated carbon, binders, and water-soluble polymers contained in the positive electrode active material, are all oxidized and burned when heated at temperatures below 500°C in an oxygen-containing atmosphere (e.g., air atmosphere). On the other hand, alkali metal compounds do not lose mass even in an oxygen-containing atmosphere up to a temperature 50°C below the melting point of alkali metal carbonate. Therefore, the weight ratio W of alkali metal compounds contained in the solid components of the positive electrode slurry A [% by mass] can be calculated using the following formula (4). W A =W4 / W2×100 Formula (4)

[0206] <Method for quantifying alkali metal compounds in positive electrode precursor> The method for quantifying the alkali metal compounds contained in the positive electrode precursor is described below. The positive electrode precursor is washed with distilled water, and the alkali metal compounds can be quantified from the change in the weight of the positive electrode before and after washing with distilled water. The area of ​​the positive electrode precursor to be measured is not particularly limited, but a 5 cm area is used to reduce measurement variability. 2 More than 200cm 2 It is preferable that it is less than 25 cm, and more preferably 2 More than 150cm 2 The area is 5cm or less. 2 If the area is 200cm or more, the reproducibility of the measurement is ensured. 2 The upper and lower limits of the area range of the positive electrode precursor to be measured can be combined arbitrarily.

[0207] The following describes a method for quantifying the alkali metal compounds in the positive electrode active material layer of the positive electrode precursor. The weight of the cut positive electrode precursor is measured and recorded as M0 [g]. Next, the positive electrode is thoroughly immersed in distilled water in an amount 100 times the weight of the positive electrode precursor (100 M0 [g]) at 25°C for at least three days to dissolve the alkali metal compounds into the water. It is preferable to take measures such as covering the container to prevent the distilled water from volatilizing. After immersion for at least three days, the positive electrode precursor is removed from the distilled water (when measuring the above-mentioned ion chromatography, adjust the liquid volume so that the amount of distilled water is 100 M0 [g]) and then vacuum-dried. Vacuum-drying conditions, such as a temperature of 100 to 200°C, a pressure of 0 to 10 kPa, and a time of 5 to 20 hours, are preferred, so that the residual water content in the positive electrode precursor is 1% by mass or less. The residual water content can be quantified using the Karl Fischer method. The weight of the positive electrode precursor after vacuum drying is designated as M1 [g]. Next, to measure the weight of the current collector of the obtained positive electrode precursor, the positive electrode active material layer on the current collector is removed using a spatula, brush, or paintbrush. If the weight of the obtained positive electrode current collector is designated as M2 [g], the weight ratio X [mass%] of the alkali metal compound contained in the active material layer of the positive electrode precursor can be calculated using equation (5). X=100×(M0-M1) / (M0-M2) Formula (5)

[0208] <Method for determining alkali metal elements: ICP-MS> In the case of positive electrode slurry, the solid component, or in the case of positive electrode precursor, is acid-decomposed using a strong acid such as concentrated nitric acid, concentrated hydrochloric acid, or aqua regia, and the resulting solution is diluted with pure water to an acid concentration of 2% to 3%. Acid decomposition can also be performed by heating or pressurizing as appropriate. The resulting diluted solution is analyzed by ICP-MS, but it is preferable to add a known amount of an element as an internal standard. If the alkali metal element to be measured exceeds the upper limit of measurable concentration, it is preferable to further dilute the diluted solution while maintaining the acid concentration. Each element can be quantified based on the obtained measurement results using a calibration curve previously prepared using standard solutions for chemical analysis.

[0209] <Average particle diameters X1 and Y1 of alkali metal compound and positive electrode active material> The average particle diameters X1 and Y1 of the alkali metal compound and the positive electrode active material in the positive electrode slurry or positive electrode precursor can be measured by any method. For example, the average particle diameters X1 and Y1 can be calculated from images of the cross section of the positive electrode precursor obtained by scanning electron microscopy (SEM) and scanning electron microscopy / energy dispersive X-ray spectroscopy (SEM-EDX) in the state of the positive electrode precursor formed as a coating on a positive electrode current collector. The positive electrode cross section can be formed, for example, by broad ion beam (BIB) processing, in which an Ar beam is irradiated from above the positive electrode precursor to create a smooth cross section along the edge of a shielding plate placed directly above the sample. The carbonate ion distribution can also be determined by Raman imaging of the cross section of the positive electrode precursor.

[0210] (Method for distinguishing between alkali metal compounds and positive electrode active materials) Alkali metal compounds and positive electrode active materials can be distinguished by oxygen mapping of SEM-EDX images of the cross section of a positive electrode precursor measured at a magnification of 1000x to 4000x. Regarding the measurement conditions for SEM-EDX images, it is preferable to adjust the brightness and contrast so that no pixels reach the maximum brightness and the average brightness falls within the range of 40% to 60%. For the obtained oxygen mapping, particles containing bright areas binarized based on the average brightness value at 50% or more in area can be distinguished as alkali metal compounds.

[0211] (Calculation method for X1 and Y1) X1 and Y1 can be determined by image analysis of a cross-sectional SEM-EDX image obtained by measuring the same field of view as the cross-sectional SEM of the positive electrode precursor. Particles X of the alkali metal compound identified in the SEM image of the cross-section of the positive electrode precursor and other particles are defined as particles Y of the positive electrode active material. The cross-sectional area S is determined for all particles X and Y observed in the cross-sectional SEM image, and the particle diameter d is calculated using the following formula (6). d=2×(S / π) 1 / 2 Formula (6) {where pi is the constant of the circumference of a circle.}

[0212] Using the obtained particle diameter d, the volume average particle diameters X0 and Y0 are calculated using the following formula (7). X0(Y0)=Σ[4 / 3π×(d / 2)] 3 ×d] / Σ[4 / 3π×(d / 2)] 3 ] Formula (7)

[0213] Measurements are taken at five or more points in different fields of view on the cross section of the positive electrode precursor, and the average values ​​of X0 and Y0 are taken as the average particle diameters X1 and Y1.

[0214] <Method for identifying binder> There is no particular limitation on the method for identifying the binder contained in the positive electrode active material layer in the positive electrode precursor or the positive electrode slurry. For example, FT-IR (Fourier transform infrared spectroscopy) measurement can be used to identify fluorine-containing substances. Fluorine-containing substances can be identified by observing the CF absorption of the obtained IR spectrum. Other analytical methods include: 19 F-solid state NMR, 19 The binder can also be identified by using F-solution NMR, etc. Furthermore, as a method for identifying rubber-based polymers, for example, Py-GC / MS (pyrolysis gas chromatography / mass spectrometry) measurement can be used. It is preferable to combine multiple analytical techniques to identify the binder.

[0215] <Method for quantifying binder> The method for quantifying the amount of binder contained in the positive electrode active material layer in the positive electrode precursor or the positive electrode slurry is not particularly limited, and can be measured, for example, by thermogravimetry (TG). Here is an example of a method for quantifying the binder using TG. In the case of a positive electrode precursor, the positive electrode active material layer is scraped onto a platinum pan and heated at a rate of 2 to 10°C / min in an air atmosphere, and the amount of binder contained in the positive electrode active material layer can be quantified from the weight loss. In the case of a positive electrode slurry, the positive electrode slurry is dried in the air and / or vacuum dried to volatilize the solvent and obtain only the solid content. The obtained solid content is scraped onto a platinum pan and heated at a rate of 2 to 10°C / min in an air atmosphere, and the amount of binder contained in the positive electrode slurry solid content can be quantified from the weight loss. For example, in the case of PVdF, the amount can be determined from the weight loss due to decomposition in an air atmosphere at temperatures up to 400 to 500°C.

[0216] For example, the amount of fluorine-containing substances can be determined by subjecting the positive electrode active material layer scraped from the positive electrode precursor to combustion ion chromatography using a tubular combustion method, as described above, based on the amount of fluoride ions. For example, in the case of PVdF, the amount of PVdF can be calculated by multiplying the measured amount of fluoride ions by 64(CH2CF2) / 38(2F).

[0217] Furthermore, the quantitative determination of rubber-based polymers can be carried out by, for example, subjecting the positive electrode active material layer scraped off from the positive electrode precursor in the same manner as described above, or the solid content obtained by volatilizing the solvent from the positive electrode slurry, to pyrolysis gas chromatography / mass spectrometry (Py-GC / MS) measurement. The amount of the binder is preferably determined by a combination of a plurality of analytical techniques.

[0218] <Weight average molecular weight of binder> The method for measuring the weight-average molecular weight of the binder contained in the positive electrode active material layer in the positive electrode precursor or the positive electrode slurry is not particularly limited, but can be measured, for example, by GPC (gel permeation chromatography). The following is an example of a method for measuring the weight-average molecular weight of the binder when using GPC.

[0219] In the case of a positive electrode precursor, the binder is extracted from the positive electrode active material layer with a solvent such as NMP (N-methylpyrrolidone) or DMF (dimethylformamide). The resulting solution is adjusted with an eluent such as DMF to a polymer concentration of approximately 1 mg / ml, then filtered, and the filtrate is used as a GPC measurement sample. In the case of a positive electrode slurry, the positive electrode slurry is adjusted with an eluent such as DMF to a polymer concentration of approximately 1 mg / ml, then filtered, and the filtrate is used as a GPC measurement sample. If necessary, heating and pressure may be applied to promote dissolution of the binder.

[0220] The column used in GPC measurement is not particularly limited as long as it can efficiently separate the sample components. The detector is not particularly limited as long as it can measure the molecular weight of the sample with high sensitivity. An RI (differential refractometer) detector can be used to detect changes in refractive index associated with changes in solute components, thereby obtaining information about the average molecular weight or molecular weight distribution of the contained polymer. The weight-average molecular weight of the binder polymer can be calculated by processing the data in the device.

[0221] In addition to the binder, other polymers such as water-soluble polymers may be present in the positive electrode active material layer or the positive electrode slurry. It is sufficient if they can be detected separately from the binder in the GPC measurement data, but even if it is difficult to separate them from the binder, it is preferable that the weight average molecular weight of the binder and dispersion stabilizer combined in the positive electrode active material layer be the above-mentioned value.

[0222] <Method for identifying water-soluble polymers> The method for identifying the water-soluble polymer contained in the positive electrode active material layer in the positive electrode precursor or the positive electrode slurry is not particularly limited, and may be, for example, 13 Examples of measurement methods include C-NMR and FT-IR. It is preferable to identify water-soluble polymers by combining multiple analytical methods.

[0223] <Quantitative method for water-soluble polymers> The method for quantifying the water-soluble polymer contained in the positive electrode active material layer in the positive electrode precursor or the positive electrode slurry is not particularly limited, and can be measured, for example, by thermogravimetry (TG). Here is an example of a method for quantifying the water-soluble polymer using TG. In the case of a positive electrode precursor, the positive electrode active material layer is scraped onto a platinum pan and heated at a rate of 2 to 10°C / min in an air atmosphere, and the water-soluble polymer contained in the positive electrode active material layer can be quantified from the weight loss. In the case of a positive electrode slurry, the positive electrode slurry is air-dried and / or vacuum-dried to volatilize the solvent and obtain only the solid content. The obtained solid content is scraped onto a platinum pan and heated at a rate of 2 to 10°C / min in an air atmosphere, and the water-soluble polymer contained in the positive electrode slurry solid content can be quantified from the weight loss. For example, in the case of carboxymethyl cellulose, the weight loss can be determined from the weight loss due to decomposition in an air atmosphere at temperatures below 300 to 350°C.

[0224] <Total amount of acidic functional groups in the positive electrode precursor> The method for measuring the total amount of acidic functional groups in the positive electrode active material layer obtained by immersing the positive electrode precursor in water for 24 hours and then removing it is described below. First, the positive electrode precursor is immersed in water at 25°C for 24 hours. The area of ​​the positive electrode precursor to be measured is not particularly limited, but in order to reduce the variation in the measurement, a 50 cm 2 More than 500cm 2 It is preferable that the length is less than 100 cm, and more preferably less than 100 cm. 2 More than 300cm 2 The area is 50cm 2 If the area is 500cm or more, the reproducibility of the measurement is ensured. 2 If the area of ​​the positive electrode precursor is less than 100%, the sample is easy to handle. The upper and lower limits of the area range of the positive electrode precursor to be measured can be arbitrarily combined. The amount of water used for immersion is not particularly limited as long as it is sufficient to dissolve the alkali metal compound contained in the positive electrode precursor. However, immersion in water in an amount at least 10 times the product of the content and solubility of the alkali metal compound is preferred. The water is not particularly limited, but distilled water or ion-exchanged water is preferred. After immersion for 24 hours, the positive electrode precursor is removed from the immersion water, the immersion water remaining on the surface is washed with fresh water, and the positive electrode precursor is vacuum-dried. If the positive electrode active material layer has peeled off from the positive electrode precursor, the positive electrode active material layer is removed by filtration from the immersion water and then vacuum-dried. Vacuum drying conditions, for example, are preferably a temperature of 100 to 200°C, a pressure of 0 to 10 kPa, and a time of 5 to 20 hours, under which the residual moisture content in the positive electrode precursor is 1% by mass or less. The residual moisture content can be quantified by the Karl Fischer method. After vacuum drying, if the current collector remains on the positive electrode precursor, the current collector is removed using a spatula, brush, paintbrush, or the like. Next, the resulting vacuum-dried cathode active material layer was weighed, a sodium hydroxide solution was added, and the mixture was stirred and allowed to stand at 25°C for at least 48 hours. The sample was allowed to settle, and the filtrate was back-titrated with hydrochloric acid to calculate the sodium hydroxide consumption (mmol / g). The stirring and standing time after the addition of the sodium hydroxide solution was preferably sealed with a lid, more preferably in a nitrogen atmosphere, to eliminate the influence of carbon dioxide in the air. Next, the total amount of acidic functional groups in the cathode active material layer, which was removed after immersion in water for 24 hours, was calculated using the following formula, according to the method described in H.P. Boehm, E. Diehl, W. Heck, and R. Sappok, Advances in Catalysis, 16, 179 (1966)). Total amount of acidic functional groups = Sodium hydroxide consumption [mmol / g]

[0225] <Total amount of acidic functional groups in positive electrode slurry> The positive electrode slurry is dried to remove the solvent, and the solid matter is taken out after immersion in water for 24 hours. The method for measuring the total amount of acidic functional groups is described below. First, the positive electrode slurry sample is dried to volatilize the solvent and obtain only the solid. The drying method and conditions are not particularly limited, but a multi-stage drying method using a combination of air drying and vacuum drying is used. The drying temperature is preferably in the range of 60 to 200°C, and the residual solvent amount is preferably 1% by mass or less, more preferably 0.5% by mass or less. The residual solvent amount can be quantified using GC / MS (gas chromatography / mass spectrometry) when the solvent is an organic solvent medium, or using the Karl Fischer method when the solvent is an aqueous medium. Next, the solid sample from which the solvent has been removed is immersed in water for 24 hours in an environment of 25° C. The weight used for measuring the solid sample from which the solvent has been removed from the positive electrode slurry is not particularly limited, but from the viewpoint of reducing the variation in the measurement, it is preferably 5 g or more and 200 g or less, and more preferably 20 g or more and 100 cm 2The weight is 5 g or more to ensure measurement reproducibility. A weight of 200 g or less provides excellent sample handling. The upper and lower limits of the weight range used for measuring the solid sample can be arbitrarily combined. The amount of water used for immersion is not particularly limited as long as it is sufficient to dissolve the alkali metal compound contained in the positive electrode slurry, but immersion in water in an amount at least 10 times the product of the alkali metal compound content and solubility is preferred. The water is not particularly limited, but distilled water or ion-exchanged water is preferred. After immersion for 24 hours, the immersion water is filtered while washing with fresh water to obtain a solid, which is then vacuum-dried. Vacuum-drying conditions, for example, are preferably a temperature of 100 to 200°C, a pressure of 0 to 10 kPa, and a time of 5 to 20 hours, under which the residual moisture content in the solid is 1% by mass or less. The residual moisture content can be quantified using the Karl Fischer method. The vacuum-dried solid material obtained above was weighed, sodium hydroxide solution was added, and the mixture was stirred and left to stand at 25°C for at least 48 hours. The sample was allowed to settle, and the filtrate was back-titrated with hydrochloric acid to calculate the sodium hydroxide consumption (mmol / g). The stirring and standing after the addition of the sodium hydroxide solution was preferably sealed with a lid to eliminate the influence of carbon dioxide in the air, and more preferably in a nitrogen atmosphere. Next, according to the method described in the literature (H.P. Boehm, E. Diehl, W. Heck, and R. Sappok, Advances in Catalysis, 16, 179 (1966)), the positive electrode slurry was dried to remove the solvent, and the total amount of acidic functional groups in the solid material extracted after immersion in water for 24 hours was calculated using the following formula: Total amount of acidic functional groups = Sodium hydroxide consumption [mmol / g]

[0226] <Solvent soaking time> The penetration time when 3 μL of a mixed solvent of ethylene carbonate:methyl ethyl carbonate = 33:67 (volume ratio) is dropped onto the positive electrode precursor is determined by measuring the time from when 3 μL of the mixed solvent is dropped all at once with a dropper onto the surface of the positive electrode active material layer of the positive electrode precursor until the mixed solvent penetrates into the positive electrode active material layer and the gloss of the surface of the positive electrode active material layer disappears (i.e., until the mixed solvent disappears from the surface of the positive electrode active material layer).

[0227] <Volume resistivity and interface resistance> In this embodiment, the positive electrode precursor has a positive electrode active material layer on one or both sides of the positive electrode current collector. The method for measuring the volume resistivity of the positive electrode active material layer of the positive electrode precursor and the interface resistance between the positive electrode active material layer and the positive electrode current collector is not particularly limited. For example, measurements can be made using an electrode resistance measurement system (an electrode resistance measuring device for positive and negative electrode sheets of lithium-ion secondary batteries) manufactured by Hioki E.E. Corporation. A measurement probe is brought into contact with the surface of the positive electrode active material layer of the positive electrode precursor at normal pressure, a constant current (1 mA) is applied to the surface of the positive electrode active material layer, and the potential distribution generated on the surface is measured at multiple points to calculate the volume resistivity of the positive electrode active material layer in the positive electrode precursor and the interface resistance between the positive electrode active material layer and the positive electrode current collector. When positive electrode active material layers are present on both sides of the positive electrode current collector, the volume resistivity and interface resistance of the side contacted by the measurement probe can be measured. To measure the volume resistivity and interface resistance of the other side, the positive electrode precursor is turned over and measured again.

[0228] <Peel strength> The peel strength of the positive electrode active material layer of the positive electrode precursor is not particularly limited, and can be measured by a known method. For example, a peel test in accordance with JIS Z0237 (2009) "Test methods for adhesive tapes and adhesive sheets" may be used, or the test method used in the examples described below may be used. [Example]

[0229] Hereinafter, the embodiments of the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to the following examples and comparative examples in any way.

[0230] <Preparation of positive electrode active material> [Preparation of activated carbon 1] The crushed coconut shell carbonized material was carbonized in a small carbonization furnace in nitrogen at 450°C for 3 hours to obtain a carbonized material. The obtained carbonized material was placed in an activation furnace, and 1 kg / h of steam was preheated in the furnace before being introduced into the activation furnace and heated to 800°C over 8 hours for activation. After activation, the carbonized material was removed and cooled under a nitrogen atmosphere to obtain activated activated carbon. The obtained activated carbon was washed with water for 10 hours and then drained. After drying for 10 hours in an electric dryer maintained at 115°C, activated carbon 1 was obtained by pulverizing it in a ball mill for 1 hour.

[0231] The average particle diameter of this activated carbon 1 was measured using a laser diffraction particle size distribution analyzer (SALD-2000J) manufactured by Shimadzu Corporation, and was found to be 4.8 μm. The pore size distribution was measured using a pore size distribution analyzer (AUTOSORB-1 AS-1-MP) manufactured by Yuasa Ionics Corporation. As a result, the BET specific surface area was found to be 2250 m 2 / g, mesopore volume (V1) is 0.50 cm 3 / g, micropore volume (V2) is 0.84 cm 3 / g, V1 / V2=0.60.

[0232] [Preparation of activated carbon 2] The crushed coconut shell carbonized material was carbonized in a small carbonization furnace in nitrogen at 600°C for 3 hours to obtain a carbonized material. The obtained carbonized material was placed in an activation furnace, and 1 kg / h of steam was preheated in the furnace before being introduced into the activation furnace. The temperature was raised to 1000°C over 5 hours for activation. After activation, the carbonized material was removed and cooled under a nitrogen atmosphere to obtain activated activated carbon. The obtained activated carbon was washed with water for 10 hours and then drained. After drying for 10 hours in an electric dryer maintained at 115°C, activated carbon 2 was obtained by pulverizing it in a ball mill for 1 hour.

[0233] The average particle diameter of this activated carbon 2 was measured using a laser diffraction particle size distribution analyzer (SALD-2000J) manufactured by Shimadzu Corporation, and was found to be 8.5 μm. The pore size distribution was measured using a pore size distribution analyzer (AUTOSORB-1 AS-1-MP) manufactured by Yuasa Ionics Corporation. As a result, the BET specific surface area was found to be 1920 m 2 / g, mesopore volume (V1) is 0.35 cm 3 / g, micropore volume (V2) is 0.75 cm 3 / g, V1 / V2=0.47.

[0234] [Preparation of activated carbon 3] Phenolic resin was carbonized in a nitrogen atmosphere in a calcination furnace at 580°C for 2 hours, then pulverized in a ball mill and classified to obtain a carbonized product with an average particle size of 6.8 μm. This carbonized product was mixed with KOH in a mass ratio of 1:5 and activated by heating in a nitrogen atmosphere in a calcination furnace at 800°C for 1 hour to obtain activated activated carbon. The activated carbon was washed with stirring in dilute hydrochloric acid adjusted to a concentration of 2 mol / L for 1 hour, then boiled and washed with distilled water until the pH stabilized between 5 and 6, and dried to obtain activated carbon 3.

[0235] The average particle diameter of this activated carbon 3 was measured using a laser diffraction particle size distribution analyzer (SALD-2000J) manufactured by Shimadzu Corporation, and was found to be 6.7 μm. The pore size distribution was measured using a pore size distribution analyzer (AUTOSORB-1 AS-1-MP) manufactured by Yuasa Ionics Corporation. As a result, the BET specific surface area was found to be 3328 m 2 / g, mesopore volume (V1) is 1.55 cm 3 / g, micropore volume (V2) is 2.01 cm 3 / g, V1 / V2=0.77.

[0236] [Preparation of activated carbon 4] Phenolic resin was carbonized in a nitrogen atmosphere in a calcination furnace at 700°C for 2 hours, then pulverized in a ball mill and classified to obtain a carbonized product with an average particle size of 11.8 μm. This carbonized product was mixed with KOH in a mass ratio of 1:4 and activated by heating in a nitrogen atmosphere in a calcination furnace at 650°C for 3 hours to obtain activated activated carbon. The activated carbon was washed with stirring in dilute hydrochloric acid adjusted to a concentration of 2 mol / L for 1 hour, then boiled and washed with distilled water until the pH stabilized between 5 and 6, and dried to obtain activated carbon 4.

[0237] The average particle diameter of this activated carbon 4 was measured using a laser diffraction particle size distribution analyzer (SALD-2000J) manufactured by Shimadzu Corporation, and was found to be 11.5 μm. The pore size distribution was measured using a pore size distribution analyzer (AUTOSORB-1 AS-1-MP) manufactured by Yuasa Ionics Corporation. As a result, the BET specific surface area was found to be 2684 m 2 / g, mesopore volume (V1) is 1.12 cm 3 / g, micropore volume (V2) is 1.48 cm 3 / g, V1 / V2=0.76.

[0238] <Production of positive electrode slurry and positive electrode precursor>

[0239] [Production of positive electrode slurry (composition a) and positive electrode precursor (composition a)] Any one of the activated carbons 1 to 4 obtained above was used as a positive electrode active material to produce a positive electrode slurry (composition a) and a positive electrode precursor (composition a) by the following method.

[0240] 62.3 parts by mass of any one of activated carbons 1 to 4, 26.3 parts by mass of lithium carbonate or the like having an average particle size shown in Table 1 as an alkali metal compound, 4.3 parts by mass of furnace black, 1.2 parts by mass of CMC (carboxymethyl cellulose) shown in Table 1, 1.8 parts by mass of PVP (polyvinylpyrrolidone), and distilled water were kneaded at 60 rpm using a kneader Hibismix manufactured by PRIMIX Co., Ltd. Then, 4.1 parts by mass of the polymer shown in Table 1 (solid content equivalent, added as an aqueous dispersion with a concentration of 40% by mass) and distilled water were added as a binder in an appropriate amount so that the solid content weight ratio was 34% by mass, and kneaded under conditions of 20 rpm to obtain a positive electrode slurry (composition a). The positive electrode slurry was applied to one side and both sides of a 15 μm-thick aluminum foil at a coating speed of 1 m / s using a die coater manufactured by Toray Engineering Co., Ltd., dried at a drying temperature of 100°C, and then pressed using a roll press at a pressure of 4 kN / cm and a surface temperature of the press part of 25°C to obtain a positive electrode precursor (composition a).

[0241] [Production of positive electrode slurry (composition b) and positive electrode precursor (composition b)] A positive electrode slurry (composition b) and a positive electrode precursor (composition b) were obtained in the same manner as for the positive electrode slurry (composition a) and the positive electrode precursor (composition a), except that 48.0 parts by mass of any one of activated carbons 1 to 4, 40.0 parts by mass of lithium carbonate, 3.0 parts by mass of furnace black, 1.8 parts by mass of CMC, 2.2 parts by mass of PVP, 5.0 parts by mass of a polymer, and distilled water were charged to give a solids weight ratio of 36 mass%.

[0242] [Production of positive electrode slurry (composition c) and positive electrode precursor (composition c)] A positive electrode slurry (composition c) and a positive electrode precursor (composition c) were obtained in the same manner as for the positive electrode slurry (composition a) and the positive electrode precursor (composition a), except that 54.2 parts by mass of any one of activated carbons 1 to 4, 33.5 parts by mass of lithium carbonate, 3.5 parts by mass of furnace black, 0.7 parts by mass of CMC, 0.3 parts by mass of PVP, 7.8 parts by mass of the polymer, and distilled water were charged to give a solids weight ratio of 38% by mass.

[0243] [Manufacture of Positive Electrode Slurry (Composition d) and Positive Electrode Precursor (Composition d)] Positive electrode slurry (Composition d) and positive electrode precursor (Composition d) were obtained in the same manner as the positive electrode slurry (Composition a) and positive electrode precursor (Composition a), except that any one of activated carbons 1 to 4 was charged in an amount of 71.3 parts by mass, lithium carbonate in an amount of 14.6 parts by mass, furnace black in an amount of 3.0 parts by mass, CMC in an amount of 3.3 parts by mass, PVP in an amount of 3.8 parts by mass, polymer in an amount of 4.0 parts by mass, and distilled water was charged to make the solid content weight ratio 30% by mass.

[0244] [Manufacture of Positive Electrode Slurry (Composition e) and Positive Electrode Precursor (Composition e)] Positive electrode slurry (Composition e) and positive electrode precursor (Composition e) were obtained in the same manner as the positive electrode slurry (Composition a) and positive electrode precursor (Composition a), except that any one of activated carbons 1 to 4 was charged in an amount of 83.6 parts by mass, lithium carbonate in an amount of 8.0 parts by mass, furnace black in an amount of 5.9 parts by mass, CMC in an amount of 0.2 parts by mass, PVP in an amount of 0.1 parts by mass, polymer in an amount of 2.2 parts by mass, and distilled water was charged to make the solid content weight ratio 40% by mass.

[0245] [Manufacture of Positive Electrode Slurry (Composition f) and Positive Electrode Precursor (Composition f)] Positive electrode slurry (Composition f) and positive electrode precursor (Composition f) were obtained in the same manner as the positive electrode slurry (Composition a) and positive electrode precursor (Composition a), except that any one of activated carbons 1 to 4 was charged in an amount of 34.6 parts by mass, lithium carbonate in an amount of 51.9 parts by mass, furnace black in an amount of 1.0 parts by mass, CMC in an amount of 3.0 parts by mass, PVP in an amount of 1.5 parts by mass, polymer in an amount of 8.0 parts by mass, and distilled water was charged to make the solid content weight ratio 26% by mass.

[0246] <<Example 1>> [Manufacture of Positive Electrode Slurry] Positive electrode slurry 1 was obtained with the above Composition a using activated carbon 1, as well as lithium carbonate, CMC1, and polymer 1 shown in Table 1.

[0247] [Measurement of pH] A 100 mL portion of the positive electrode slurry 1 was dispensed into a container (150 mL volume, cylindrical), and the sample temperature was kept at 25°C. A Horiba, Ltd. portable pH meter D-71 was used as the pH meter. The pH meter was calibrated using a neutral phosphate pH standard solution and a borate pH standard solution, and the pH meter electrode was then washed with water. The pH meter electrode was then immediately immersed in the dispensed positive electrode slurry 1, and the pH was measured. The results are shown in Table 1.

[0248] <Calculation of η2 / η1, η3 / η2, and η4 / η3> The positive electrode slurry 1 was measured using an Anton Paar rheometer MCR102 at a temperature of 25°C and a shear rate of 5 s -1 , 50s -1 , 500s -1 , and 2000s -1 The viscosity was measured under the above conditions, and η1, η2, η3, and η4 were calculated from the viscosity after 1 minute. η2 / η1, η3 / η2, and η4 / η3 were calculated from the obtained η1, η2, η3, and η4. The results are shown in Table 1.

[0249] <Measurement of the total amount of acidic functional groups in the positive electrode slurry> Approximately 140 g of the positive electrode slurry 1 was dispensed into a metal container, and the metal container was placed in a hot air dryer. Slurry Sample 1 was dried at 120°C until the liquid surface lost its gloss. It was then further vacuum-dried at 150°C and 3 kPa for 12 hours to obtain Slurry Solid Component Sample 1. Slurry Solid Component Sample 1 was then immersed in 1 L of ion-exchanged water for 24 hours, and the immersion water was filtered while being washed with fresh ion-exchanged water to obtain Post-Immersion Solid Sample 1. Post-Immersion Solid Sample 1 was then vacuum-dried at 150°C and 3 kPa for 12 hours. After vacuum drying, the positive electrode current collector was removed using a spatula, brush, and paintbrush, and Post-Vacuum Drying Sample 1 was obtained. Next, approximately 0.5 g of vacuum-dried sample 1 was weighed into a sample bottle, 80 mL of 0.05 mol / L sodium hydroxide solution was added, and the mixture was stirred under a nitrogen atmosphere and left to stand at 25°C for 50 hours to allow the sample to settle. The filtrate was then back-titrated with 0.02 mol / L hydrochloric acid using an AT-700M automatic titrator manufactured by Kyoto Electronics Manufacturing Co., Ltd., and the total amount of acidic functional groups was calculated using the method described above. The results are shown in Table 1.

[0250] <Production of positive electrode precursor> Using the above positive electrode slurry 1, a double-sided positive electrode precursor 1 and a single-sided positive electrode precursor 1 having the above composition a were obtained. The thickness of the positive electrode active material layer of the obtained double-sided and single-sided positive electrode precursor 1 was determined by subtracting the thickness of the aluminum foil from the average value of thicknesses measured at any 10 locations on the double-sided and single-sided positive electrode precursor 1 using a film thickness meter, Linear Gauge Sensor GS-551, manufactured by Ono Keiki Co., Ltd. As a result, the thickness of the positive electrode active material layer of the double-sided and single-sided positive electrode precursor 1 was 70 μm per side.

[0251] <Measurement of the total amount of acidic functional groups in the positive electrode precursor> The above double-sided positive electrode precursor 1 was cut into a size of 7.5 cm x 30 cm to obtain Sample 1, which was then immersed in 1 L of ion-exchanged water for 24 hours. Sample 1 was then removed from the immersion water, and the remaining immersion water on the surface was washed twice with fresh ion-exchanged water. Sample 1 was then vacuum-dried for 12 hours at 150°C and 3 kPa. After vacuum drying, the positive electrode current collector was removed using a spatula, brush, and paintbrush, and Sample 1 was obtained after vacuum drying. Next, approximately 0.5 g of vacuum-dried sample 1 was weighed into a sample bottle, 80 mL of 0.05 mol / L sodium hydroxide solution was added, and the mixture was stirred under a nitrogen atmosphere and left to stand at 25°C for 50 hours to allow the sample to settle. The filtrate was then back-titrated with 0.02 mol / L hydrochloric acid using an AT-700M automatic titrator manufactured by Kyoto Electronics Manufacturing Co., Ltd., and the total amount of acidic functional groups was calculated using the method described above. The results are shown in Table 1.

[0252] <Measurement of solvent penetration time> A 3 μL volumetrically mixed solvent of ethylene carbonate and methyl ethyl carbonate (volume ratio: 33:67) was dropped onto the surface of the positive electrode active material layer of the double-sided positive electrode precursor 1 using a dropper, and the time required for the mixed solvent to penetrate into the positive electrode active material layer and for the surface gloss of the positive electrode active material layer to disappear (i.e., for the mixed solvent to disappear from the surface of the positive electrode active material layer) was measured. The results are shown in Table 1.

[0253] <Measurement of volume resistivity and interface resistance> Using the electrode resistance measurement system RM2610 manufactured by Hioki Electric Co., Ltd., a measurement probe was brought into contact with the surface of the positive electrode active material layer of the above double-sided positive electrode precursor 1 at normal pressure, a constant current (1 mA) was passed through the surface of the positive electrode active material layer, and the potential distribution generated on the surface was measured at multiple points to calculate the volume resistivity of the positive electrode active material layer in the positive electrode precursor and the interfacial resistance between the positive electrode active material layer and the positive electrode current collector. The obtained results are shown in Table 1.

[0254] <Measurement of peel strength> The above double-sided positive electrode precursor 1 was cut into a width of 25 mm and a length of 120 mm (100 mm is the positive electrode active material layer, and the remaining 20 mm is the uncoated part where the positive electrode active material layer is not coated). A cellophane tape (registered trademark, CT405AP-24 manufactured by Nichiban Co., Ltd.) with a width of 24 mm was cut into a length of 100 mm and pasted on the positive electrode active material layer. Using a tensilon (STB-1225S manufactured by A&D Co., Ltd.), the uncoated part of the positive electrode current collector was sandwiched on the lower clip jaw side, and the end of the cellophane tape (registered trademark) was sandwiched on the upper clip jaw side, and the peel strength was measured under the following conditions. The measurement of the peel strength was started within 3 minutes after the cellophane tape (registered trademark) was pasted on the positive electrode active material layer. · Ambient temperature: 25 °C · Sample width: 25 mm · Stroke: 100 mm · Speed: 50 mm / min · Data acquisition: Integral average load of 25 - 65 mm The measurement was performed on a total of 3 samples, and the average value was calculated. The obtained results are shown in Table 1.

[0255] <Calculation of X1 and Y1> A small piece of 1 cm × 1 cm was cut out from the above double-sided positive electrode precursor 1. Using SM-09020CP manufactured by JEOL Ltd., argon gas was used, and a cross-section perpendicular to the surface direction of the positive electrode precursor sample was prepared under the conditions of an acceleration voltage of 4 kV and a beam diameter of 500 μm. Gold was coated on the cross-section by sputtering in a vacuum of 10 Pa. Subsequently, SEM-EDX of the positive electrode cross-section was measured under the conditions shown below in the atmosphere exposure. (SEM-EDX measurement conditions) Measurement equipment: Hitachi High-Technologies, field emission scanning electron microscope FE-SEM S-4700 Acceleration voltage: 10kV Emission current: 1μA ·Measurement magnification: 2000x Electron beam incident angle: 90° ·X-ray extraction angle: 30° Dead time: 15% Mapping elements: C, O, F Measurement pixel count: 256 x 256 pixels Measurement time: 60 seconds. Number of times accumulated: 50 The brightness and contrast were adjusted so that no pixels reach maximum brightness and the average brightness is within the range of 40% to 60%. (SEM-EDX analysis) The SEM-EDX image of the positive electrode cross section measured above was analyzed using image analysis software (ImageJ) by the method described above to calculate X1 and Y1. The results are shown in Table 1.

[0256] <Preparation of negative electrode active material> BET specific surface area is 3.4m 2 150 g of commercially available artificial graphite with a % saturation of 1 / g and an average particle size of 5.1 μm was placed in a stainless steel mesh basket and placed on a stainless steel tray containing 15 g of coal-based pitch (softening point: 50°C). Both were then placed in an electric furnace (effective furnace dimensions: 300 mm x 300 mm x 300 mm). The temperature was raised to 1000°C over 8 hours in a nitrogen atmosphere and held at that temperature for 4 hours, causing a thermal reaction between the two, yielding composite carbon material 1. Subsequently, the material was naturally cooled to 60°C, and then composite carbon material 1 was removed from the furnace.

[0257] The average particle size and BET specific surface area of ​​the obtained composite carbon material 1 were measured by the same method as above. As a result, the average particle size was 5.0 μm and the BET specific surface area was 6.5 m. 2 The mass ratio of the carbonaceous material derived from coal pitch to the artificial graphite was 2%.

[0258] <Production of negative electrodes> Using the composite carbon material 1 as the negative electrode active material, a negative electrode 1 was produced as follows. 80 parts by mass of composite carbon material 1, 8 parts by mass of acetylene black, 12 parts by mass of PVdF (polyvinylidene fluoride), and NMP (N-methylpyrrolidone) were mixed, and the mixture was dispersed using a thin-film swirling high-speed mixer, Filmix, manufactured by PRIMIX Corporation, at a peripheral speed of 15 m / s to obtain a coating solution. The viscosity (ηb) and TI value of the resulting coating solution were measured using a Toki Sangyo Co., Ltd. E-type viscometer, TVE-35H. The viscosity (ηb) was 2,548 mPa·s and the TI value was 2.5. The coating solution was applied to both sides of a 10 μm-thick electrolytic copper foil using a die coater manufactured by Toray Engineering Co., Ltd., at a coating speed of 1 m / s and dried at 85°C to obtain anode 1. The resulting anode 1 was pressed using a roll press at a pressure of 4 kN / cm and a surface temperature of 25°C. The thickness of the negative electrode active material layer of the negative electrode 1 obtained above was determined by subtracting the thickness of the copper foil from the average value of thicknesses measured at 10 arbitrary locations on the negative electrode 1 using a film thickness meter, Linear Gauge Sensor GS-551, manufactured by Ono Keiki Co., Ltd. As a result, the thickness of the negative electrode active material layer of the negative electrode 1 was 45 μm per side.

[0259] <Preparation of non-aqueous electrolyte> A mixed solvent of ethylene carbonate (EC):methyl ethyl carbonate (EMC) = 33:67 (volume ratio) was used as the organic solvent, and the respective electrolyte salts were dissolved in the mixed solvent so that the concentration ratio of LiN(SO2F)2 and LiPF6 in the resulting non-aqueous electrolyte solution was 75:25 (molar ratio) and the sum of the concentrations of LiN(SO2F)2 and LiPF6 was 1.2 mol / L, thereby obtaining a non-aqueous electrolyte solution.

[0260] The concentrations of LiN(SO2F)2 and LiPF6 in the obtained nonaqueous electrolyte were 0.9 mol / L and 0.3 mol / L, respectively.

[0261] <Fabrication of non-aqueous hybrid capacitor> [Assembling and drying energy storage elements] The obtained double-sided positive electrode precursor 1, double-sided negative electrode 1, and single-sided positive electrode precursor 1 were placed in a 10 cm × 10 cm (100 cm 2 ) were cut into strips. Single-sided positive electrode precursor 1 was used for the top and bottom surfaces, and 21 sheets of double-sided negative electrode 1 and 20 sheets of double-sided positive electrode precursor 1 were used for the top and bottom surfaces. A 15 μm-thick microporous membrane separator was sandwiched between the negative electrode and positive electrode precursor. A negative electrode terminal and a positive electrode terminal were connected to the negative electrode and positive electrode precursor, respectively, by ultrasonic welding to form an electrode laminate. This electrode laminate was vacuum-dried at a temperature of 80°C, a pressure of 50 Pa, and a drying time of 60 hours. The dried electrode laminate was placed in an exterior housing made of aluminum laminate packaging in a dry environment with a dew point of -45°C, and the three sides of the exterior housing, including the electrode terminal and bottom parts, were heat-sealed at a temperature of 180°C, a sealing time of 20 seconds, and a sealing pressure of 1.0 MPa.

[0262] [Injection, impregnation and sealing of energy storage elements] Approximately 80 g of the nonaqueous electrolyte solution was injected into the electrode laminate housed in an aluminum laminate packaging material under atmospheric pressure in a dry air environment with a temperature of 25°C and a dew point of -40°C or less, forming a nonaqueous hybrid capacitor before pre-doping. The nonaqueous hybrid capacitor was then placed in a vacuum chamber, and the pressure was reduced from normal pressure to -87 kPa, then returned to atmospheric pressure, and allowed to stand for 5 minutes. This cycle of reducing the pressure from normal pressure to -87 kPa and then returning to atmospheric pressure was repeated four times, after which the energy storage element was allowed to stand for 15 minutes. The pressure was reduced from normal pressure to -91 kPa and then returned to atmospheric pressure. This cycle of reducing the pressure and returning to atmospheric pressure was repeated a total of seven times (reducing the pressure from normal pressure to -95, -96, -97, -81, -97, -97, and -97 kPa, respectively). The electrode laminate was impregnated with the nonaqueous electrolyte solution according to the above procedure.

[0263] The exterior housing containing the electrode laminate impregnated with the non-aqueous electrolyte solution was placed in a vacuum sealing machine, and the aluminum laminate packaging was sealed at a pressure of 0.1 MPa at 180°C for 10 seconds under a reduced pressure of -95 kPa, thereby obtaining a non-aqueous hybrid capacitor.

[0264] [Pre-Dope] The obtained non-aqueous hybrid capacitor was subjected to constant current charging at a current value of 0.5 A in a 35°C environment using a charge / discharge device (TOSCAT-3100U) manufactured by Toyo Systems Co., Ltd. until a voltage of 4.5 V was reached, followed by initial charging by a method in which constant voltage charging at 4.5 V was continued for 2.5 hours, and pre-doping was performed on the negative electrode.

[0265] [aging] After pre-doping, the non-aqueous hybrid capacitor was subjected to constant current discharge at 0.5 A in a 25°C environment until the voltage reached 3.0 V, and then subjected to constant current discharge at 3.0 V for 1 hour to adjust the voltage to 3.0 V. Subsequently, the non-aqueous hybrid capacitor was stored in a thermostatic chamber at 60°C for 15 hours.

[0266] [Gas release] A portion of the aluminum laminate packaging of the aged nonaqueous hybrid capacitor was opened in a dry air environment with a temperature of 25°C and a dew point of -40°C. The nonaqueous hybrid capacitor was then placed in a vacuum chamber, and a KNF diaphragm pump (N816.3KT.45.18) was used to reduce the pressure from atmospheric pressure to -80 kPa over three minutes, then return it to atmospheric pressure over three minutes. This process was repeated three times. The nonaqueous hybrid capacitor was placed in a vacuum sealing machine, and the pressure was reduced to -90 kPa. The aluminum laminate packaging was then sealed at 200°C for 10 seconds at a pressure of 0.1 MPa.

[0267] Through the above procedure, a non-aqueous hybrid capacitor was completed.

[0268] <Evaluation of non-aqueous hybrid capacitors> [Capacitance, Ra·F measurement] The capacitance F and internal resistance Ra at 25°C of the obtained nonaqueous hybrid capacitor were calculated using the method described above, using a charge / discharge device (5V, 360A) manufactured by Fujitsu Telecom Networks Ltd. in a thermostatic chamber set at 25°C, to obtain Ra·F. The results are shown in Table 1.

[0269] [Gas generation amount after high temperature storage test] The nonaqueous hybrid capacitor obtained by the above process was charged at a constant current of 100 C to 4.0 V using a Fujitsu Telecom Networks Limited charger (5 V, 360 A) in a thermostatic chamber set at 25 °C. This was followed by a constant voltage charge of 4.0 V for a total of 10 minutes. The nonaqueous hybrid capacitor was then stored at 60 °C. Every two weeks, the capacitor was removed from the 60 °C environment and charged to 4.0 V using the same charging procedure. The cell was then stored again at 60 °C. This process was repeated for three months. The cell volume Va before the storage test and the cell volume Vb after three months were measured using the Archimedes method, and the gas generation rate was calculated by subtracting Va from Va. The results are shown in Table 1.

[0270] [Calculation of Rb / Ra] The room temperature internal resistance Rb of the nonaqueous hybrid capacitor after the high-temperature storage test was calculated in the same manner as in the calculation of Ra·F above. Rb / Ra was calculated by dividing this Rb (Ω) by the internal resistance Ra (Ω) before the high-temperature storage test obtained by calculating Ra·F above. The results are shown in Table 1.

[0271] Examples 2 to 25 and Comparative Examples 1 to 10 Slurries, positive electrode precursors, and nonaqueous hybrid capacitors of Examples 2 to 25 and Comparative Examples 1 to 10 were prepared in the same manner as in Example 1, except that the positive electrode active material, alkali metal compound, CMC, and binder type, blending ratio, average particle size, and composition of the positive electrode precursor were each set as shown in Table 1, and various evaluations were performed. The obtained evaluation results are shown in Table 1.

[0272] Comparative Example 11 <Production of positive electrode precursor (composition g)> 87.5 parts by weight of activated carbon 2, 3.0 parts by weight of furnace black, 1.5 parts by weight of PVP, 3.0 parts by weight of CMC shown in Table 1, and distilled water were kneaded at 60 rpm using a PRIMIX kneader (Hibismix). Then, 5.0 parts by weight of the polymer shown in Table 1 (solid content equivalent, added as an aqueous dispersion with a concentration of 40% by weight) was added as a binder, and an appropriate amount of distilled water was added to achieve a solids weight ratio of 36% by weight, and kneaded at 20 rpm to obtain a positive electrode slurry. The positive electrode slurry was applied to one and both sides of a 15 μm thick aluminum foil using a die coater manufactured by Toray Engineering Co., Ltd. at a coating speed of 1 m / s, dried at a drying temperature of 100 ° C, and then pressed using a roll press at a pressure of 4 kN / cm and a surface temperature of 25 ° C. The resulting positive electrode slurry (composition g) and positive electrode precursor (composition g) were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0273] <Production and evaluation of non-aqueous hybrid capacitors> The assembly, injection, impregnation, and sealing of a nonaqueous hybrid capacitor were carried out in the same manner as in Example 1, except that the obtained positive electrode precursor (composition g) and a negative electrode in which a metal lithium foil equivalent to 211 mAh / g per unit mass of the negative electrode active material was attached to the surface of the negative electrode active material layer of the negative electrode 1 were used.

[0274] Next, as a pre-doping step, the nonaqueous hybrid capacitor obtained above was stored in a thermostatic chamber at an ambient temperature of 45°C for 72 hours, and the metallic lithium was ionized and doped into the negative electrode 1. The obtained nonaqueous hybrid capacitor was subjected to aging and degassing in the same manner as in Example 1 to produce a nonaqueous hybrid capacitor, which was then evaluated. The results are shown in Table 1. Comparative Example 12 A positive electrode slurry, a positive electrode precursor, and a nonaqueous hybrid capacitor of Comparative Example 12 were prepared in the same manner as in Comparative Example 11, except that the positive electrode active material was activated carbon 4, and various evaluations were performed. The results are shown in Table 1.

[0275] [Table 1-1]

[0276] [Table 1-2]

[0277] [Table 1-3]

[0278] [Table 1-4]

[0279] The abbreviations for each component in Table 1 have the following meanings: <CMC(カルボキシメチルセルロース)> CMC1: Carboxymethyl cellulose with a degree of etherification of 0.61 and a 1% by weight aqueous solution viscosity (25°C) of 1927 mPa s CMC2: Carboxymethyl cellulose with a degree of etherification of 0.71 and a 1% by weight aqueous solution viscosity (25°C) of 375 mPa·s CMC3: Carboxymethyl cellulose with a degree of etherification of 0.78 and a 1% by weight aqueous solution viscosity (25°C) of 14 mPa·s CMC4: Carboxymethyl cellulose with a degree of etherification of 0.85 and a 1% by weight aqueous solution viscosity (25°C) of 1659 mPa·s CMC5: Carboxymethyl cellulose with a degree of etherification of 1.34 and a 1% by weight aqueous solution viscosity (25°C) of 1393 mPa·s CMC6: Carboxymethyl cellulose with a degree of etherification of 0.63 and a 1% by weight aqueous solution viscosity (25°C) of 9320 mPa·s <Binder> Polymer 1: Average particle size 200 nm, oxidation resistance 4.85 V (vs. Li / Li + ) acrylic latex Polymer 2: Average particle size 100 nm, oxidation resistance 4.78 V (vs. Li / Li + ) acrylic latex Polymer 3: Average particle size 150 nm, oxidation resistance 4.58 V (vs. Li / Li+ ) styrene-butadiene copolymer Polymer 4: Oxidation resistance 4.25V (vs. Li / Li + ) sodium polyacrylate

[0280] In Table 1, "-" indicates that the component in that column was not used.

[0281] As described above, the alkali metal compounds contained in the positive electrode slurry and the positive electrode precursor decompose, and alkali metal ions that can participate in charge and discharge are pre-doped into the negative electrode or released into the electrolyte, thereby allowing the charge and discharge of the nonaqueous hybrid capacitor to proceed.

[0282] As can be seen from a comparison between Examples 1 to 25 and Comparative Examples 1 to 12, the positive electrode precursor contained an alkali metal compound other than the positive electrode active material, and the positive electrode active material layer, which was removed after immersing the positive electrode precursor in water for 24 hours, had a total amount of acidic functional groups of 0.15 mmol / g or more and 2.00 mmol / g or less per weight of the active material layer, the solvent immersion time of the positive electrode precursor was 5 seconds or more and 40 seconds or less, the volume resistivity of the positive electrode active material layer of the positive electrode precursor was 1.0 Ω cm or more and 10.0 Ω cm or less, and the interface resistance between the positive electrode active material layer and the positive electrode current collector was 0.01 Ω cm 2 More than 1.00Ω cm 2 If the peel strength of the positive electrode active material layer is 0.02 N / cm or more and 3.00 N / cm or less, when the positive electrode precursor is incorporated into a non-aqueous hybrid capacitor, it is possible to obtain a non-aqueous hybrid capacitor having a small Ra·F (low internal resistance, i.e., high input / output characteristics), and a low gas generation amount and Rb / Ra after a high-temperature storage test (excellent high-temperature storage characteristics). Furthermore, if the positive electrode precursor contains an alkali metal compound other than the positive electrode active material, is alkaline with a pH of 9.0 or more, and can be stored at a shear rate of 5 s -1 , 50s -1 , 500s -1 , and 2000s -1where η1 (mPa·s), η2 (mPa·s), η3 (mPa·s), and η4 (mPa·s) are respectively, and the total amount of acidic functional groups on the solid extracted after drying the positive electrode slurry to remove the solvent and immersing in water for 24 hours is 0.15 mmol / g or more and 2.00 mmol / g or less per solid weight, then when the positive electrode precursor formed by coating the positive electrode slurry on a positive electrode current collector is incorporated into a nonaqueous hybrid capacitor, a nonaqueous hybrid capacitor having a small Ra·F (low internal resistance, i.e., high input / output characteristics) and a low amount of gas generation and Rb / Ra after a high-temperature storage test (excellent high-temperature storage characteristics) can be obtained.

[0283] Although not wishing to be bound by theory, it is believed that by including an alkali metal compound in the positive electrode slurry and the positive electrode precursor, when the positive electrode precursor is incorporated into a nonaqueous hybrid capacitor, a suitable number of pores remain in the positive electrode after the alkali metal compound is oxidatively decomposed, thereby resulting in a nonaqueous hybrid capacitor that exhibits high input / output characteristics.

[0284] If the total amount of acidic functional groups in the positive electrode active material layer obtained by immersing the positive electrode precursor in water for 24 hours and then extracting it is 0.15 mmol / g or more per weight of the active material layer, or if the total amount of acidic functional groups in the solid material obtained by drying the positive electrode slurry to remove the solvent and then immersing it in water for 24 hours is 0.15 mmol / g or more per weight of the solid material, then it is considered that a high-input / output nonaqueous hybrid capacitor can be obtained, because the wettability of the carbon material containing activated carbon, which is the positive electrode active material, to the electrolyte is ensured, and carboxymethyl cellulose is not excessively adsorbed on the surface of the carbon material, allowing for smooth adsorption and desorption of ions. On the other hand, if the total amount of acidic functional groups in the positive electrode active material layer obtained by immersing the positive electrode precursor in water for 24 hours and then extracting it is 2.00 mmol / g or less per weight of the active material layer, or if the total amount of acidic functional groups in the solid material obtained by drying the positive electrode slurry to remove the solvent and then immersing it in water for 24 hours and then extracting it is 2.00 mmol / g or less per weight of the solid material, then it is possible to suppress the formation of a coating due to a side reaction during charging and discharging that is due to the amount of functional groups in the carbon material itself, and it is also possible to suppress the aggregation of carbon material particles, and therefore it is believed that a nonaqueous hybrid capacitor exhibiting excellent high-temperature storage properties can be obtained.

[0285] If the positive electrode precursor is soaked in the solvent for 5 seconds or longer, sufficient electrode strength can be maintained even after the oxidative decomposition of the alkali metal compound by pre-doping, resulting in a nonaqueous hybrid capacitor with excellent high-temperature storage characteristics. On the other hand, if the positive electrode precursor is soaked in the solvent for 40 seconds or shorter, the binder and water-soluble polymer do not segregate on the surface of the positive electrode precursor, but are uniformly distributed within the positive electrode active material, ensuring sufficient electrode strength and electronic conductivity, resulting in a nonaqueous hybrid capacitor with high input / output capabilities.

[0286] If the volume resistivity of the positive electrode active material layer of the positive electrode precursor is 1.0 Ω·cm or higher, an appropriate amount of voids will be maintained in the positive electrode active material layer, which will not hinder ion migration during charge and discharge, and the alkali metal compounds will be uniformly oxidized and decomposed during pre-doping, resulting in a non-aqueous hybrid capacitor with excellent high-temperature storage characteristics.On the other hand, if the volume resistivity of the positive electrode active material layer of the positive electrode precursor is 10.0 Ω·cm or lower, a sufficient conductive network will be secured within the positive electrode active material layer, which will promote the oxidative decomposition of the alkali metal compounds during pre-doping, resulting in a non-aqueous hybrid capacitor with high input / output and excellent high-temperature storage characteristics.

[0287] The interface resistance between the positive electrode active material layer and the positive electrode current collector is 0.01 Ω cm 2 If this is the case, the binder in the positive electrode active material is uniformly distributed, and sufficient electrode strength can be ensured even after the oxidative decomposition of the alkali metal compound by pre-doping, resulting in a non-aqueous hybrid capacitor with excellent high-temperature storage characteristics. On the other hand, if the interface resistance between the positive electrode active material layer and the positive electrode current collector is 1.00 Ω cm, 2 If the above conditions are met, resistors such as binders and water-soluble polymers in the positive electrode active material will not be distributed excessively unevenly at the interface between the positive electrode active material layer and the positive electrode current collector, the alkali metal compounds will be oxidized and decomposed uniformly during pre-doping, and the charge and discharge reactions will also proceed uniformly, resulting in a non-aqueous hybrid capacitor that exhibits high input / output and excellent high-temperature storage characteristics.

[0288] If the peel strength of the positive electrode active material layer is 0.02 N / cm or more, it is believed that chipping of the positive electrode active material layer due to gas generation during pre-doping can be suppressed, micro-short circuits can be suppressed, and a nonaqueous hybrid capacitor with excellent high-temperature storage properties can be obtained. On the other hand, if the peel strength of the positive electrode active material layer is 3.00 N / cm or less, the binder and water-soluble polymer are not present in excess throughout the positive electrode active material layer, or are not excessively and unevenly distributed at the interface between the positive electrode active material layer and the positive electrode current collector, and a nonaqueous hybrid capacitor with high input / output properties can be obtained.

[0289] When an alkali metal compound other than the positive electrode active material is contained and the positive electrode slurry has an alkaline pH of 9.0 or more, the alkali metal compound can exist as an alkali metal compound in the positive electrode slurry without being excessively neutralized, and therefore can exist as an alkali metal compound in the positive electrode active material layer when the positive electrode precursor is produced, and it is thought that when the positive electrode precursor is incorporated into a nonaqueous hybrid capacitor, the alkali metal compound is sufficiently decomposed by pre-doping, resulting in excellent high-temperature durability.

[0290] If η2 / η1, η3 / η2, and η4 / η3 are 0.10 or greater, the change in viscosity with respect to shear rate is suppressed, which enables uniform distribution of the coating film in the coating length and coating width directions when forming a coating film of the positive electrode precursor using a coater. This allows pre-doping of alkali metal ions into the negative electrode to proceed uniformly when assembling a nonaqueous hybrid capacitor, which is thought to result in excellent high input / output characteristics and high-temperature storage characteristics. On the other hand, if η2 / η1, η3 / η2, and η4 / η3 are 1.00 or less, carboxymethyl cellulose is sufficiently adsorbed onto the surface of the carbon material, thereby suppressing aggregation of carbon material particles due to a lack of carboxymethyl cellulose on the surface of the carbon material, resulting in excellent dispersion stability of the positive electrode slurry. Furthermore, by bonding carboxymethyl cellulose particles together in the positive electrode precursor with a binder, sufficient electrode strength can be ensured, and the carbon material and alkali metal compound can be uniformly distributed within the positive electrode active material layer without localization. Therefore, when the positive electrode is incorporated into a nonaqueous hybrid capacitor, charge / discharge reactions proceed uniformly within the positive electrode active material layer. Furthermore, since the surface of the carbon material is moderately coated with carboxymethyl cellulose, side reactions are also suppressed, resulting in excellent high-temperature durability. [Industrial Applicability]

[0291] The positive electrode slurry and positive electrode precursor of the present invention can be suitably used as a positive electrode precursor for a nonaqueous hybrid capacitor in, for example, the field of hybrid drive systems for automobiles, applications for assisting instantaneous power peaks, etc. The nonaqueous hybrid capacitor of the present invention is preferred when applied as a lithium ion capacitor, because the effects of the present invention are maximized.

Claims

1. A positive electrode precursor having a positive electrode current collector and a positive electrode active material layer on one or both surfaces of the positive electrode current collector, the positive electrode active material layer containing a positive electrode active material, an alkali metal compound other than the positive electrode active material, a binder, and a water-soluble polymer; the positive electrode active material is a carbon material, the carbon material includes activated carbon, and the water-soluble polymer includes carboxymethyl cellulose; the positive electrode precursor is immersed in water for 24 hours, and then the positive electrode active material layer is taken out. A sodium hydroxide solution is added to the positive electrode active material layer, and the total amount of acidic functional groups in the positive electrode active material layer is calculated by back titration using hydrochloric acid, and the total amount of acidic functional groups in the positive electrode active material layer is 0.15 mmol / g or more and 2.00 mmol / g or less by weight of the positive electrode active material layer, the penetration time when 3 μL of a mixed solvent of ethylene carbonate:methyl ethyl carbonate=33:67 (volume ratio) is dropped onto the positive electrode precursor is 5 seconds or more and 40 seconds or less, The volume resistivity of the positive electrode active material layer of the positive electrode precursor is 1.0 Ω cm or more and 10.0 Ω cm or less, and the interface resistance between the positive electrode active material layer and the positive electrode current collector is 0.01 Ω cm ２ 1.00Ω・cm or more ２ is less than or equal to, and The positive electrode precursor, wherein the positive electrode active material layer has a peel strength of 0.02 N / cm or more and 3.00 N / cm or less.

2. 2 . The positive electrode precursor according to claim 1 , wherein the proportion of the water-soluble polymer relative to the total mass of the carbon material contained in the positive electrode active material layer is 0.5% by mass or more and 10.0% by mass or less.

3. 3. The positive electrode precursor according to claim 1, wherein the alkali metal compound is at least one selected from the group consisting of lithium carbonate, sodium carbonate, and potassium carbonate.

4. 3. The positive electrode precursor of claim 1, wherein the alkali metal compound is lithium carbonate.

5. The positive electrode precursor according to claim 1 or 2, wherein the positive electrode active material layer contains the alkali metal compound in an amount of 10% by mass to 50% by mass.

6. The binder is 4.3 V (vs. Li / Li ＋ 3. The positive electrode precursor according to claim 1, having an oxidation resistance of at least 100%.

7. 3. The positive electrode precursor according to claim 1, wherein the binder is an acrylic latex.

8. The activated carbon has a mesopore volume derived from pores with a diameter of 20 Å or more and 500 Å or less calculated by the BJH method, V １ (cm ３ / g), the amount of micropores derived from pores with a diameter of less than 20 Å calculated by the MP method is V ２ (cm ３ / g), 0.3<V １ ≦0.8, and 0.5≦V ２ ≦1.0 and the specific surface area measured by the BET method is 1,500 m ２ / g or more 3,000m ２ The positive electrode precursor according to claim 1 or 2, wherein the SiO 2 content is 1 / g or less.

9. The activated carbon has a mesopore volume V derived from pores with a diameter of 20 Å or more and 500 Å or less calculated by the BJH method. １ (cm ３ / g) is 0.8<V １ ≦2.5, and the micropore volume V derived from pores with a diameter of less than 20 Å calculated by the MP method ２ (cm ３ / g) is 0.8<V ２ ≦3.0 and the specific surface area measured by the BET method is 2,300 m ２ / g or more 4,000m ２ The positive electrode precursor according to claim 1 or 2, wherein the SiO 2 content is 1 / g or less.

10. The average particle diameter of the alkali metal compound is X １ When this is the case, 0.1 μm≦X １ ≦10 μm, and the average particle diameter of the positive electrode active material is Y １ When Y is 2 μm or less, １ ≦20 μm, and X １ <Y １ The positive electrode precursor according to claim 1 or 2,

11. The positive electrode precursor according to claim 1 or 2, which is used for producing a positive electrode of a non-aqueous hybrid capacitor.

12. A slurry containing a positive electrode active material, an alkali metal compound other than the positive electrode active material, a binder, a water-soluble polymer, and a solvent, the positive electrode active material is a carbon material, the carbon material includes activated carbon, and the water-soluble polymer includes carboxymethyl cellulose; The slurry is alkaline with a pH of 9.0 or more, The shear rate of the slurry is 5 s －１ , 50s －１ , 500s －１ , and 2000s －１ The viscosity at η １ (mPa s), η ２ (mPa s), η ３ (mPa s), and η ４ (mPa·s), 0.10≦η ２ / η １ ≦1.00 and 0.10≦η ３ / η ２ ≦1.00 and 0.10≦η ４ / η ３ ≦1.00, The slurry is dried to remove the solvent, and the slurry is immersed in water for 24 hours. A sodium hydroxide solution is added to the solid matter extracted from the slurry, and the total amount of acidic functional groups in the solid matter calculated by back titration with hydrochloric acid is 0.15 mmol / g or more and 2.00 mmol / g or less per weight of the solid matter.

13. The slurry according to claim 12, wherein a proportion of the water-soluble polymer relative to the total mass of the carbon material contained in the slurry is 0.5 mass % or more and 10.0 mass % or less.

14. 14. The slurry according to claim 12 or 13, wherein the alkali metal compound is one or more selected from the group consisting of lithium carbonate, sodium carbonate, and potassium carbonate.

15. 14. The slurry of claim 12 or 13, wherein the alkali metal compound is lithium carbonate.

16. The slurry according to claim 12 or 13, wherein the proportion of the alkali metal compound relative to the total mass of all solids excluding the solvent in the slurry is 10 mass % or more and 50 mass % or less.

17. The slurry according to claim 12 or 13, wherein the binder has an oxidation resistance of 4.3 V (vs. Li / Li+) or more.

18. 14. The slurry of claim 12 or 13, wherein the binder is an acrylic latex.

19. The activated carbon has a mesopore volume derived from pores with a diameter of 20 Å or more and 500 Å or less calculated by the BJH method, V １ (cm ３ / g), the amount of micropores derived from pores with a diameter of less than 20 Å calculated by the MP method is V ２ (cm ３ / g), 0.3<V １ ≦0.8, and 0.5≦V ２ ≦1.0 and the specific surface area measured by the BET method is 1,500 m ２ / g or more 3,000m ２ The slurry according to claim 12 or 13, wherein the SiO 2 content is 0.1g or less.

20. The activated carbon has a mesopore volume V derived from pores with a diameter of 20 Å or more and 500 Å or less calculated by the BJH method. １ (cm ３ / g) is 0.8<V １ ≦2.5, and the micropore volume V derived from pores with a diameter of less than 20 Å calculated by the MP method ２ (cm ３ / g) is 0.8<V ２ ≦3.0 and the specific surface area measured by the BET method is 2,300 m ２ / g or more 4,000m ２ The slurry according to claim 12 or 13, wherein the SiO 2 content is 0.1g or less.

21. The average particle diameter of the alkali metal compound is X １ When this is the case, 0.1 μm≦X １ ≦10 μm, and the average particle diameter of the positive electrode active material is Y １ When Y is 2 μm or less, １ ≦20 μm, and X １ <Y １ 14. The slurry of claim 12 or 13, wherein:

22. The slurry according to claim 12 or 13, which is for producing a positive electrode of a non-aqueous hybrid capacitor.

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