Power storage device and method for manufacturing the same

Abstract

To provide a power storage device having high density and high capacity, and to provide a method of manufacturing the same.SOLUTION: Thereafter, a high-voltage treatment in which a voltage higher than an upper limit of a working voltage is applied for a certain period of time is performed in a state in which volume expansion is suppressed, so that an electrode density of the graphene film is 0. 4g / cm3 or more and an interlayer spacing d in a C-axis direction of graphene in the graphene film measured by an X-ray diffraction method is 0. 38nm or more.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electricity storage device using a graphene material for electrodes, and a method for manufacturing the same. [Background technology]

[0002] Graphene is sp 2 Graphene is a sheet-like material with a two-dimensional network structure in which carbon atoms are bonded hexagonally, and is highly conductive, strong, and heat-resistant. It has therefore attracted attention in a variety of fields, including electronics, biomedical materials, and aerospace materials. In particular, for high-energy-density power storage devices such as lithium-ion capacitors and lithium-ion batteries, various graphene-based electrodes have been proposed with the aim of increasing capacity, improving voltage resistance, and further improving energy density and power density (see Patent Documents 1 and 2).

[0003] For example, Patent Document 1 describes a capacitor electrode using a graphene porous carbon sheet formed from a graphene porous carbon material such as graphene meso-sponge and carbon nanotubes. Patent Document 2 describes an electrode formed using an electrode material that includes a graphene composite in which carbon nanotubes exist between graphene layers, has a carbon atom to oxygen atom ratio (C / O) of 7 or more as measured by X-ray photoelectron spectroscopy, and contains less than 20% by mass of carbon nanotubes (excluding 0% by mass).

[0004] In addition, in the past, in order to improve the energy density, a peak A derived from the G band was observed in the Raman spectrum by Raman spectroscopy at least in the active material of the negative electrode, and the half width of the peak A was 50 cm -1 As described above, a diffraction peak B originating from the (002) plane is observed around 2θ=26° in a diffraction profile obtained by X-ray diffraction (XRD), and a capacitor using graphene in which the interlayer distance derived from this diffraction peak B is 0.330 nm or more and 0.360 nm or less has been proposed (see Patent Document 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 080520 [Patent Document 2] Japanese Patent Application Publication No. 2023-170689 [Patent Document 3] Japanese Patent Publication No. 2023-131624 Summary of the Invention [Problem to be solved by the invention]

[0006] However, graphene materials have a strong tendency to be re-laminate during the electrode fabrication process, and therefore, in electrodes using the porous graphene material described in Patent Document 1, particularly when attempting to form a high-density electrode film, there is a problem in that the pores of the porous graphene are clogged by the re-lamination, weakening the effect of promoting electrolyte transport and reducing capacity. Similarly, the graphene material described in Patent Document 3 is also prone to change in its lamination state during the electrode fabrication process, and when incorporated into a capacitor, the interlayer distance is reduced, which may prevent the expected energy density from being obtained.

[0007] In contrast, the electrode material described in Patent Document 2 has carbon nanotubes between the graphene layers, and therefore can maintain a constant interlayer distance even during the electrode fabrication process. However, recent energy storage devices require further improvements in the performance of electrode materials.

[0008] Therefore, an object of the present invention is to provide a high-density, high-capacity electricity storage device and a method for manufacturing the same. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present inventors conducted extensive experimental studies and found that, by performing a specific treatment after manufacturing an electricity storage device, it is possible to expand the spaces between layers of graphene material constituting an electrode, thereby increasing the capacity of the electricity storage device, and thus arrived at the present invention.

[0010] That is, the electricity storage device according to the present invention has an electrode film using a graphene material as an active material, and the electrode film has a density of 0.4 g / cm 3 The interlayer distance in the C-axis direction of graphene measured by X-ray diffraction is 0.38 nm or more. The graphene material is, for example, a composite of graphene and carbon nanotubes. The electrode film may contain a binder resin, and may also contain a conductive material. The electricity storage device of the present invention is, for example, a lithium ion capacitor or an electric double layer capacitor.

[0011] The method for producing an electricity storage device according to the present invention is a method for producing an electricity storage device including an electrode film using a graphene material as an active material, and includes a high-voltage treatment step of sealing an electrode body including the electrode film and an electrolyte with an exterior material, and then applying a voltage higher than an upper limit of a working voltage for a certain period of time in a state in which volume expansion is suppressed, and the electrode film after the high-voltage treatment step has an electrode density of 0.4 g / cm 3 The interlayer distance in the C-axis direction of graphene measured by X-ray diffraction is 0.38 nm or more. In the method for producing an electricity storage device of the present invention, a composite of graphene and carbon nanotubes may be used as the graphene material. When the electricity storage device is a lithium ion capacitor, a voltage of, for example, 4.5 V or more may be applied for 30 minutes or more in the high voltage treatment step. When the electricity storage device is an electric double layer capacitor, a voltage of, for example, 3.5 V or more may be applied for 30 minutes or more in the high voltage treatment step. In the high voltage treatment step, charging and discharging at a high voltage may be repeated multiple times. The high voltage treatment step can be carried out in an environment of 10° C. or less. [Effects of the Invention]

[0012] According to the present invention, the capacity of an electricity storage device can be increased without reducing the volumetric energy density of the electrode. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram showing an example of the structure of a composite of graphene and carbon nanotubes. FIG. [Figure 2] FIG. 10 is a schematic diagram showing a state in which the interlayer distance is increased by high voltage treatment. [Figure 3] 1 shows the results of X-ray diffraction measurements of the electrode films of Example 2, Comparative Example 1, and Reference Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0015] In the electricity storage device according to the embodiment of the present invention, a graphene material is used as the active material, and the density of the electrode film (electrode density) is 0.4 g / cm 3 The above conditions are satisfied, and the graphene in the electrode film has an interlayer distance in the C-axis direction of 0.38 nm or more as measured by X-ray diffraction (XRD).

[0016] [Graphene materials] In the electricity storage device of this embodiment, examples of graphene materials used as the active material include graphene produced by various methods such as mechanical exfoliation, chemical vapor deposition (CVD), lamination on a silicon carbide (SiC) substrate, and chemical oxidation-reduction, composites of graphene and other carbon materials, and composites of graphene and metals. From the viewpoint of improving energy density, however, a composite of graphene and carbon nanotubes (hereinafter also referred to as a graphene / CNT composite) is preferred.

[0017] <Graphene / CNT composite> Fig. 1 is a schematic diagram showing an example of the structure of a composite of graphene and carbon nanotubes. The graphene / CNT composite used in the electricity storage device of this embodiment may be a composite of graphene and carbon nanotubes (CNTs), and its structure is not particularly limited. For example, a graphene / CNT composite 10 shown in Fig. 1 may have a structure in which a single layer or several layers of graphene 1 are stacked with CNTs 2 interposed therebetween.

[0018] In the graphene / CNT composite 10 shown in Fig. 1, the graphenes 1 are regularly arranged at equal intervals and parallel to each other, but the present invention is not limited to this, and the graphenes 1 may be arranged randomly. Similarly, in Fig. 1, the CNTs 2 are arranged parallel to each other in the in-plane direction, but the present invention is not limited to this, and the graphenes 1 may be arranged randomly between the layers of graphene 1.

[0019] Furthermore, the type of CNT2 is not particularly limited and may be any of single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT). The size of CNT2 is not particularly limited, but from the viewpoint of promoting uniform dispersion of CNTs in graphene and more efficiently combining with graphene1, the length is preferably 1 to 20 μm, and the average outer diameter is preferably 0.4 to 5.0 nm, more preferably 1.0 to 3.0 nm.

[0020] Graphene 1 is characterized by its tendency to aggregate due to π-π stacking. However, in graphene / CNT composite 10, CNT2 present between the layers of graphene 1 in a single-layer or few-layer stack structure functions as a spacer, preventing restacking and ensuring a high specific surface area. Furthermore, when processed into an electrode, electrolyte flows into the gaps between the graphene 1 layers, making it easier for electrolyte ions to adsorb to the graphene surface. Furthermore, graphene / CNT composite 10 also has high through-thickness electrical conductivity because CNT2, which has high electrical conductivity, is present between the graphene 1 layers.

[0021] [Electrode density] The electrode film of the electricity storage device of this embodiment has a density (electrode density) of 0.4 g / cm 3 The density of the electrode film is 0.4 g / cm 3 If it is less than this, the volume energy density of the electrode will be low, and the performance as an electricity storage device will be insufficient.

[0022] [Graphene interlayer distance d] In the power storage device of this embodiment, the interlayer distance in the C-axis direction of the graphene contained in the electrode film is 0.38 nm or more as measured by X-ray diffraction (XRD). The interlayer distance of graphene is generally about 0.33 to 0.35 nm, and even after ions are doped between the graphene layers due to charging and discharging, it is about 0.36 nm at most.

[0023] In contrast, in the electricity storage device of this embodiment, the interlayer distance d of the graphene contained in the electrode film is 0.38 nm or more, which is longer than that of conventional graphene materials, thereby enabling the realization of a high-capacity electricity storage device.

[0024] [Other components of the electrode film] The electrode film of the electricity storage device of this embodiment may contain a conductive material and a binder resin in addition to the graphene material as an active material. The conductive material used in the electrode film of the electricity storage device of this embodiment is not particularly limited, and any known conductive material can be used. However, from the viewpoint of affinity with the graphene material, carbon materials such as carbon black, acetylene black, channel black, furnace black, and ketjen black are preferred.

[0025] The binder resin can also be appropriately selected from organic solvent-based binders and aqueous binders used in ordinary electrodes. Specific examples of organic solvent-based binders include polytetrafluoroethylene (PTFE), its modified polytetrafluoroethylene resin, and polyvinylidene fluoride (PVDF), while examples of aqueous binders include sodium carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR). Among these, it is particularly preferable to use a combination of aqueous binders, CMC and SBR.

[0026] The thickness of the electrode film is not particularly limited, but is, for example, 50 μm or less.

[0027] [Structure and types of energy storage devices] The type and structure of the electricity storage device of this embodiment are not particularly limited, as long as it has two or more electrode bodies and an electrolyte, and the above-mentioned electrode film is provided on at least one of the electrode bodies. For example, when the electricity storage device of this embodiment is a lithium ion capacitor, it has a configuration in which a positive electrode (cathode) and a negative electrode (anode) are arranged spaced apart from each other, and a Li ion electrolyte is filled between these electrodes. In this lithium ion capacitor, the above-mentioned electrode film is used for at least the positive electrode.

[0028] Furthermore, when the power storage device of this embodiment is an electric double layer capacitor, it has a configuration in which a positive electrode (cathode) and a negative electrode (anode) are disposed apart from each other in an electrolyte such as an ionic liquid such as 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI), 1-ethyl-3-methylimidazolium borofluoride (EMI-BF4), and 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPPp-TFSI), or M'OH (M' is an alkali metal), and a separator is disposed between the positive electrode and the negative electrode. In this electric double layer capacitor, the above-mentioned electrode film is used for both the positive electrode and the negative electrode.

[0029] [Manufacturing method] Next, a method for manufacturing the above-mentioned electricity storage device will be described. The electricity storage device of this embodiment can be manufactured, for example, by sealing the electrode assembly and the electrolyte with an exterior material, and then performing a high-voltage treatment step in a state where volume expansion is suppressed.

[0030] <High voltage processing> High-voltage treatment is a process in which a voltage higher than the upper limit of the operating voltage of the power storage device is applied for a certain period of time. For example, if the power storage device is a lithium ion capacitor, a voltage of 4.5 V or higher may be applied for 30 minutes or more, and if the power storage device is an electric double layer capacitor, a voltage of 3.5 V or higher may be applied for 30 minutes or more.

[0031] FIG. 2 is a schematic diagram showing a state in which the interlayer distance d has been increased by high-voltage treatment. As shown in FIG. 2, high-voltage treatment allows ions to penetrate between the graphene layers, thereby increasing the interlayer distance d of the graphene. For example, in the case of a graphene / CNT composite 10 having an interlayer distance d of 0.36 nm, high-voltage treatment can increase the interlayer distance d to approximately 0.385 nm. When the interlayer distance d of graphene is increased in this way, the amount of ion storage increases, making it possible to increase the capacity of an electricity storage device.

[0032] The higher the voltage of the high-voltage treatment and the longer the treatment time (high-voltage application time), the greater the effect of expanding the interlayer distance of graphene, but on the other hand, the electrode expands, reducing the electrode volumetric energy density and increasing the resistance value due to poor contact between the active materials. Therefore, in the manufacturing method for an electricity storage device of this embodiment, during the high-voltage treatment, pressure is applied to the periphery of the exterior material with a jig or the like to suppress the reduction in volume density due to the expansion of the electrode.

[0033] Depending on the conditions of the high-voltage treatment, the electrolyte may be decomposed to produce gas or polymers, which may result in a decrease in capacity or an increase in resistance. Therefore, the high-voltage treatment is preferably carried out in an environment of 10°C or less, and more preferably in an environment of 0°C or less. This can prevent the production of gas or polymers due to decomposition of the electrolyte.

[0034] In the high-voltage treatment step, charging and discharging at a high voltage may be repeated multiple times, thereby suppressing decomposition of the electrolyte solution and enhancing the expansion of the electrode and the interlayer expansion effect of the graphene.

[0035] As described above in detail, in the electricity storage device of this embodiment, the interlayer distance of the graphene material constituting the electrodes is set to 0.38 nm or more by high-voltage treatment, so that the amount of ions stored is increased compared to conventional electricity storage devices, and an electricity storage device with high density and high capacity can be realized. The configuration of this embodiment is particularly suitable for lithium ion capacitors and electric double layer capacitors. [Example]

[0036] The effects of the present invention will be specifically described below with reference to examples and comparative examples.

[0037] (First Example) First, as a first example of the present invention, an electric double layer capacitor using electrodes having electrode films using a graphene material on the positive and negative electrodes was subjected to a high voltage treatment by the method and conditions shown below, and the interlayer distance, capacitance, and resistance value of the graphene were measured.

[0038] <Preparation of electrodes> A mixture of raw materials (87 parts by mass of graphene / CNT composite powder, 5 parts by mass of acetylene black powder, 4 parts by mass of acrylic binder, 4 parts by weight of carboxymethyl cellulose, and 310 parts by mass of water) was thoroughly mixed to obtain a slurry. This slurry was then coated on both sides of a 15 μm-thick current collector made of carbon-coated aluminum foil using a roll coater to form an electrode film. This was then vacuum dried to obtain an electrode with a total thickness (the sum of the thickness of the electrode film on both sides and the thickness of the current collector) of 85 μm (electrode film density: 0.62 g / cm). 3 ) was obtained.

[0039] <Fabrication of electric double layer capacitor cells> Ten 30mm x 30mm positive electrodes and eleven 30mm x 30mm negative electrodes were cut from the electrodes fabricated by the method described above. These positive and negative electrodes were alternately stacked with separators in between, and separators were placed on the top and bottom of the stack. The four sides were then taped to obtain an electrode stack unit. Aluminum terminals (5mm wide, 0.1mm thick) were then placed on the terminal welds (10mm wide) of the positive and negative current collectors of this electrode stack unit and ultrasonically welded. The weld area was Yw = 3mm, Xw = 3mm.

[0040] After drying at 120°C for 12 hours, one side of the electrode terminal was folded back with the end of the electrode terminal pulled out of the exterior laminate film pouch, and the folded side was heat-sealed to one side of the terminal part of the exterior laminate film with a sealing width of 2 mm. The film was then vacuum-impregnated with EMI-BF4 (1-ethyl-3-methylimidazolium tetrafluoroborate) as an electrolyte, and the remaining side was then heat-sealed under reduced pressure with a sealing width of 2 mm, followed by vacuum sealing to assemble a film-type capacitor cell.

[0041] <High voltage processing> (1) Example 1 The cell was clamped with a jig to suppress expansion of the cell, and then charged in a thermostatic chamber at 10°C at a current of 0.2 A / g (0.2 A per 1 g of active material). When the voltage reached 3.7 V, charging at a constant current was initiated. In this state, a voltage was applied for 30 minutes, and then a current discharge was carried out at 0.2 A / g (0.2 A per 1 g of active material). This procedure was repeated three times to obtain the electricity storage device (electric double layer capacitor) of Example 1.

[0042] (2) Example 2 An electricity storage device (electric double layer capacitor) of Example 2 was obtained in the same manner and under the same conditions as in Example 1, except that the voltage was set to 4.0V.

[0043] (3) Comparative Example 1 A power storage device (electric double layer capacitor) that was not subjected to high voltage treatment was used as Comparative Example 1.

[0044] (4) Comparative Example 2 Without suppressing expansion with a jig, the cell was charged at a current of 0.2 A / g (0.2 A per 1 g of active material) in a thermostatic chamber at 10°C, and when the voltage reached 3.7 V, charging at a constant current was initiated. In this state, voltage was applied for 6 hours, and then current discharge was carried out at 0.2 A / g (0.2 A per 1 g of active material). This operation was repeated three times to obtain an electricity storage device (electric double layer capacitor) of Comparative Example 2.

[0045] <Measurement of electrode film density> The density of the electrode film in the cell was measured after each of the energy storage devices of the Examples and Comparative Examples was completely discharged, the cell was disassembled, and the electrode film was removed from the exterior material. The electrode film was washed with ethanol to remove adsorbed electrolyte, and then vacuum dried at 120°C for 12 hours.

[0046] <Measurement of the interlayer distance of graphene> The interlayer distance of graphene in the electrode film in the cell was determined from the results of X-ray diffraction measurements of each electrode film that had been removed from the cell, washed with ethanol, and then vacuum-dried at 120°C for 12 hours.

[0047] <Capacitance measurement> The capacitance of the electric double layer capacitor cell was measured at room temperature in a potential range of 0 to 3.2 V, and the capacitance per unit weight, C (F / g), was calculated based on the following formula 1. In the following formula 1, I (A) is the constant current, m (g) is the total mass of the two electrodes, and dV / dt (V / s) is the slope obtained by linear fitting of the discharge curve between Vmax (the voltage at the start of discharge) and 1 / 2Vmax.

[0048]

number

[0049] The results are shown in Table 1. The "electrode volume energy density" shown in Table 1 is the amount of energy per 1 L of electrode volume, and the "electrode volume" here is the combined volume of the positive and negative electrodes incorporated in the cell.

[0050] [Table 1]

[0051] FIG. 3 shows the results of X-ray diffraction measurements of the electrode films of Example 2, Comparative Example 1, and Reference Example 1. As shown in FIG. 3, for the electrode film (Reference Example 1) before incorporation into a cell, a diffraction peak corresponding to the C-axis (002) plane of graphene was observed near 2θ = 24.7°, and the calculated interlayer distance in the C-axis direction was 0.360 nm. In contrast, for the electrode film of Example 2, which was subjected to high-voltage treatment, a diffraction peak corresponding to the C-axis (002) plane of graphene was observed near 2θ = 23.1°, and the calculated interlayer distance in the C-axis direction was 0.385 nm. On the other hand, for the electrode film of Comparative Example 1, which was not subjected to high-voltage treatment, a diffraction peak corresponding to the C-axis (002) plane of graphene of the electrode film was observed near 2θ = 23.8°, and the calculated interlayer distance in the C-axis direction was 0.373 nm.

[0052] Furthermore, as shown in Table 1 above, the electricity storage devices of Examples 1 and 2, which underwent high-voltage treatment while suppressing volume expansion, had higher specific capacitances than the electricity storage device of Comparative Example 1, which was not subjected to high-voltage treatment, confirming that the capacity had been increased. Furthermore, the electricity storage devices of Examples 1 and 2 did not show an increase in resistance value and still had good DC resistance. As a result, the electrode volume energy density of the electricity storage devices of Examples 1 and 2 increased to 16 Wh / L (Example 1) to 19 Wh / L (Example 2), and the time constant (ΩF value) was 0.78 to 1.1.

[0053] On the other hand, the electricity storage device of Comparative Example 2, which was subjected to high voltage treatment without suppressing volume expansion, had a specific capacitance of 142 F / g and an electrode film density of 0.12 g / cm 3 The electrode volume energy density was reduced to 4.9 Wh / L, the resistance was high, and the time constant (ΩF value) was 7.7, which was inferior in performance to the electricity storage devices of Examples 1 and 2.

[0054] (Second Example) Next, as a second example of the present invention, a lithium ion capacitor using an electrode having an electrode film using a graphene material as a positive electrode was subjected to high voltage treatment by the method and conditions shown below, and the interlayer distance, capacitance, and resistance value of the graphene were measured.

[0055] <Preparation of electrodes> (1) Positive electrode A mixture of 87 parts by mass of graphene / CNT composite powder, 5 parts by mass of acetylene black powder, 4 parts by mass of acrylic binder, 4 parts by mass of carboxymethyl cellulose, and 310 parts by mass of water was thoroughly mixed to obtain a slurry. This slurry was then coated on both sides of a 31 μm-thick aluminum perforated foil current collector using a roll coater to form a positive electrode film. This was then vacuum dried to produce an electrode with a total thickness (the sum of the thickness of the positive electrode film on both sides and the thickness of the positive electrode current collector) of 85 μm (electrode film density: 0.68 g / cm). 3 ) was obtained.

[0056] (2) Negative electrode A mixture of 88 parts by weight of Nikabeads P5B-GP powder, 5 parts by weight of acetylene black powder, 3 parts by weight of SBR (styrene butadiene rubber) binder, 4 parts by weight of carboxymethyl cellulose, and 210 parts by weight of water was thoroughly mixed to obtain a slurry. This slurry was then coated on both sides of a 21 μm-thick copper foil current collector using a roll coater to form a negative electrode film. This was then vacuum dried to obtain an electrode with a total thickness (the sum of the thickness of the negative electrode film on both sides and the thickness of the negative electrode current collector) of 77 μm.

[0057] <Fabrication of lithium ion capacitor cells> Ten pieces measuring 29 mm x 29 mm were cut out from the positive electrode prepared by the method described above, and eleven pieces measuring 30 mm x 30 mm were cut out from the negative electrode, and these positive and negative electrodes were alternately stacked with separators between them and dried for 12 hours at a temperature of 120°C. Then, separators were placed on the top and bottom and taped on all four sides, and one piece of lithium metal pressed onto copper lath was placed on the outermost side of the electrode stack unit so as to face the positive electrode, thereby obtaining an electrode stack unit.

[0058] An aluminum positive electrode terminal (5 mm wide) was then placed on the terminal weld (10 mm wide) of the positive electrode current collector of this electrode laminate unit and ultrasonically welded. A nickel negative electrode terminal (5 mm wide) was placed on the terminal weld (10 mm wide) of the copper lath that had pressure-bonded the negative electrode current collector and lithium metal foil and ultrasonically welded. The weld area was Yw = 3 mm, Xw = 3 mm. One side of the electrode terminal was folded back with the end of the electrode terminal pulled out of the exterior laminate film pouch, and the folded back side was heat-sealed to one side of the terminal part of the exterior laminate film with a sealing width of 2 mm.

[0059] The electrolyte was then vacuum-impregnated with 1M LiPF6 / EC (Ethylene Carbonate):DEC (DEC:Diethyl Carbonate) = 1:1 (volume ratio). The remaining edges were then heat-sealed under reduced pressure with a sealing width of 2 mm, and a lithium-ion capacitor cell was assembled by vacuum sealing. The cell was left for 14 days after assembly, and the cell voltage was measured to be 2.4 V or higher, indicating that lithium ions had been pre-doped into the negative electrode.

[0060] <High voltage processing> (1) Example 3 With the cell sandwiched between jigs to prevent expansion of the cell, the cell was charged at a current of 0.2 A / g (0.2 A per 1 g of active material) in a thermostatic chamber at 0° C., and constant current charging was initiated when the voltage reached 4.5 V. In this state, voltage was applied for 6 hours, and then current discharge was carried out at 0.2 A / g (0.2 A per 1 g of active material), to obtain an electricity storage device (lithium ion capacitor) of Example 3.

[0061] (2) Example 4 An electricity storage device (lithium ion capacitor) of Example 4 was obtained in the same manner and under the same conditions as in Example 3, except that the voltage was set to 4.8V.

[0062] (3) Example 5 An electricity storage device (lithium ion capacitor) of Example 5 was obtained in the same manner and under the same conditions as in Example 3, except that the voltage was set to 5.0V.

[0063] (4) Comparative Example 3 A power storage device (lithium ion capacitor) that was not subjected to high voltage treatment was used as Comparative Example 3.

[0064] <Capacitance measurement> The capacitance of the lithium ion capacitor cell was measured at room temperature in the potential range of 2.2 to 4.2 V. Specifically, the cell was charged at a constant current of 0.2 A / g (0.2 A per 1 g of active material) until the cell voltage reached 4.2 V, and then discharged at a constant current of 0.2 A / g (0.2 A per 1 g of active material) until the cell voltage reached 2.2 V. The capacitance was evaluated from this 4.2 V-2.2 V cycle.

[0065] The results are shown in Table 2. The "electrode volume energy density" shown in Table 2 is the amount of energy per 1 L of electrode volume, and the "electrode volume" here is the combined volume of the positive electrode and negative electrode incorporated in the cell.

[0066] [Table 2]

[0067] As shown in Table 2 above, the electricity storage devices of Examples 3 to 5, which had undergone high-voltage treatment, had higher specific capacities than the electricity storage device of Comparative Example 3, which had not undergone low-temperature high-voltage treatment, confirming that the capacity had increased. Furthermore, the electricity storage devices of Examples 3 to 5 did not show an increase in resistance value and still had good DC resistance. As a result, the electrode volume energy density of the electricity storage devices of Examples 3 to 5 increased to 50 Wh / L (Example 3) to 66 Wh / L (Example 5), and the time constant (ΩF value) was 1.3 to 1.7.

[0068] From the above results, it was confirmed that according to the present invention, the capacity of an electricity storage device can be increased without reducing the volumetric energy density of the electrode.

[0069] The present invention can also have the following configuration. [1] The electrode film has a graphene material as an active material, The electrode film is Density is 0.4g / cm 3 That's all, The interlayer distance of graphene in the C-axis direction measured by X-ray diffraction is 0.38 nm or more. Energy storage device. [2] The electricity storage device according to [1], wherein the graphene material is a composite of graphene and carbon nanotubes. [3] The electricity storage device according to [1] or [2], wherein the electrode film contains a binder resin. [4] The electricity storage device according to any one of [1] to [3], wherein the electrode film further contains a conductive material. [5] The electricity storage device according to any one of [1] to [4], which is a lithium ion capacitor or an electric double layer capacitor. [6] A method for manufacturing an electricity storage device including an electrode film using a graphene material as an active material, a high-voltage treatment step of applying a voltage higher than the upper limit of a working voltage for a certain period of time while suppressing volume expansion after sealing the electrode body including the electrode film and the electrolyte with an exterior material; The electrode film after the high voltage treatment step has an electrode density of 0.4 g / cm 3 The method for producing an electricity storage device as described above, wherein the interlayer distance in the C-axis direction of graphene measured by X-ray diffraction is 0.38 nm or more. [7] The method for manufacturing an electricity storage device according to [6], wherein a composite of graphene and carbon nanotubes is used as the graphene material. [8] the electricity storage device is a lithium ion capacitor, The method for producing an electricity storage device according to [6] or [7], wherein a voltage of 4.5 V or more is applied for 30 minutes or more in the high voltage treatment step. [9] the electricity storage device is an electric double layer capacitor, The method for producing an electricity storage device according to [6] or [7], wherein in the high voltage treatment step, a voltage of 3.5 V or more is applied for 30 minutes or more.

[10] The method for producing an electricity storage device according to any one of [6] to [9], wherein in the high voltage treatment step, charging and discharging at a high voltage are repeated multiple times.

[11] The method for producing an electricity storage device according to any one of [6] to

[10] , wherein the high voltage treatment step is carried out in an environment of 10° C. or less.

Claims

1. The electrode film has a graphene material as an active material, The electrode film is Density is 0.4 g / cm ３ That's all, The interlayer distance of the graphene in the C-axis direction measured by X-ray diffraction is 0.38 nm or more. Energy storage device.

2. The electricity storage device according to claim 1 , wherein the graphene material is a composite of graphene and carbon nanotubes.

3. The electricity storage device according to claim 1 , wherein the electrode film contains a binder resin.

4. The electricity storage device according to claim 1 , wherein the electrode film further includes a conductive material.

5. 2. The electricity storage device according to claim 1, which is a lithium ion capacitor or an electric double layer capacitor.

6. A method for manufacturing an electricity storage device including an electrode film using a graphene material as an active material, a high-voltage treatment step of applying a voltage higher than the upper limit of a working voltage for a certain period of time while suppressing volume expansion after sealing the electrode body including the electrode film and the electrolyte with an exterior material; The electrode film after the high voltage treatment step has an electrode density of 0.4 g / cm ３ The method for manufacturing an electricity storage device, wherein the interlayer distance in the C-axis direction of graphene measured by X-ray diffraction is 0.38 nm or more.

7. The method for manufacturing an electricity storage device according to claim 6 , wherein a composite of graphene and carbon nanotubes is used as the graphene material.

8. the electricity storage device is a lithium ion capacitor, The method for manufacturing an electricity storage device according to claim 6 , wherein in the high voltage treatment step, a voltage of 4.5 V or more is applied for 30 minutes or more.

9. the electricity storage device is an electric double layer capacitor, The method for manufacturing an electricity storage device according to claim 6 , wherein in the high voltage treatment step, a voltage of 3.5 V or more is applied for 30 minutes or more.

10. The method for producing an electricity storage device according to claim 6 , wherein in the high voltage treatment step, charging and discharging at a high voltage are repeated multiple times.

11. The method for producing an electricity storage device according to claim 6 , wherein the high voltage treatment step is carried out in an environment of 10° C. or less.

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