WO2016190225A1 - Electrode material, method for producing same, and electricity storage device using same - Google Patents

Abstract

The objective of the present invention is to provide: an electrode material which improves the rate characteristics of an electricity storage device that uses an ionic liquid as an electrolyte; a method for producing this electrode material; and an electricity storage device which uses this electrode material. An electrode material according to the present invention contains a laminate wherein reduced graphene oxides are laminated; and the laminate contains an ionic liquid between the reduced graphene oxides.

Description

Electrode material, method for producing the same, and power storage device using the same

The present invention relates to an electrode material using graphene oxide, a manufacturing method thereof, and an electricity storage device using the same.

Electrical storage devices such as electric double layer capacitors and lithium ion batteries are attracting attention because of their large capacities. In an electricity storage device using graphene as an electrode material, it is expected to use an ionic liquid having a large potential window as an electrolyte. However, since the ionic liquid has large molecules, high viscosity, and low conductivity, the rate capability of the ionic liquid to graphene is low. For this reason, even if an ionic liquid is used for an electrical storage device, quick charge / discharge cannot be performed.

In order to solve such a problem, there is a technique in which a mixture obtained by mixing an ionic liquid and solvent molecules is used as an electrolyte (see, for example, Non-Patent Document 1). According to Non-Patent Document 1, N-butyl-n-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide (PYR ₁₄ TFSI) as an ionic liquid, acetonitrile, butylnitrile, benzonitrile, propylene carbonate as solvent molecules, The conductivity can be improved by adding dimethyl carbonate or the like.

As another technique, there is a technique in which a mixture of an ionic liquid and a single-walled nanotube is used as an electrolyte (see, for example, Non-Patent Document 2). According to Non-Patent Document 2, the conductivity can be improved by adding single-walled nanotubes to 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF ₄ ) as an ionic liquid.

However, both Non-Patent Document 1 and Non-Patent Document 2 are aimed at improving the characteristics of ionic liquids for power storage devices, and attention has not been paid to electrode materials.

An object of the present invention is to provide an electrode material that improves rate characteristics in an electricity storage device using an ionic liquid as an electrolyte, a manufacturing method thereof, and an electricity storage device using the electrode material.

The electrode material including a laminate in which reduced graphene oxide is laminated according to the present invention includes an ionic liquid between the reduced graphene oxide, thereby achieving the above-described problem.
The weight ratio of the ionic liquid to the reduced graphene oxide may be in the range of 0.01 to 1.00.
The weight ratio of the ionic liquid to the reduced graphene oxide may be in the range of 0.02 to 0.60.
The specific surface area of the laminate may be in the range of 350 m ² / g to 500 m ² / g.
The specific surface area of the laminate may be 420 m ² / g or more and 450 m ² / g or less.
The pore volume of the laminate may be in the range of 0.75 cc / g to 1.5 cc / g.
The pore volume of the laminate may be in the range of 0.85 cc / g to 0.95 cc / g.
The ionic liquids are 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF ₄ ), 1-ethyl-3-methylimidazolium-bis (fluorosulfonyl) imide (EMIFSI), 1-ethyl-3-methylimidazole Rium-bis (trifluoromethanesulfonyl) imide (EMITFSI), 1-butyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (BMITSI), 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIBF ₄ ) , 1-hexyl-3-methylimidazolium - bis (trifluoromethanesulfonyl) imide (HMITFSI), 1-ethyl-3-methylimidazolium - fluorohydrocarbon oxygenate _{(EMI (FH) 2.3 F)} , N, N Diethyl -N- methyl -N- (2-methoxyethyl) - tetrafluoroborate (DEMEBF _4), N, N- diethyl--N- methyl -N- (2-methoxyethyl) - bis (trifluoromethanesulfonyl) imide ( DEMETFSI), N-methyl-N-propylpiperidinium-bis (trifluoromethanesulfonyl) imide (PP13TFSI), triethylsulfonium-bis (trifluoromethanesulfonyl) imide (TESTFSI), N-methyl-Npropylpyrrolidinium-bis (Trifluoromethanesulfonyl) imide (P13TFSI), triethyloctylphosphonium-bis (trifluoromethanesulfonyl) imide (P2228TFSI), N-methyl-methoxymethylpyrrolidinium-tetrafluorovole (C13BF ₄ ), lithium-bis (fluorosulfonyl) imide (LiFSI), and lithium-bis (trifluoromethanesulfonyl) imide (LiTFSI) may be selected.
The laminate may have mesopores having a diameter in the range of 2 nm to 6 nm and macropores having a diameter of 50 nm or more.
The laminate may have a specific capacity in the range of 80 F / g or more and 140 F / g or less at a current density of 20 A / g.
A method for producing an electrode material according to the present invention includes the steps of preparing a suspension obtained by adding graphene oxide and an ionic liquid to a polar solvent, and adding a reducing agent to the suspension followed by refluxing. This achieves the above-mentioned problem.
In the preparing step, a weight ratio of the ionic liquid to the graphene oxide may be 0.005 or more and 0.5 or less.
In the preparing step, the weight ratio of the ionic liquid to the graphene oxide may be 0.01 or more and 0.3 or less.
The polar solvent may be selected from the group consisting of water, dimethyl sulfoxide (DMSO), N, N-dimethylsulfamide (DMF) and ethanol.
The ionic liquid includes 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF ₄ ), 1-ethyl-3-methylimidazolium-bis (fluorosulfonyl) imide (EMIFSI), 1-ethyl-3-methylimidazole Rium-bis (trifluoromethanesulfonyl) imide (EMITFSI), 1-butyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (BMITSI), 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIBF ₄ ) 1-hexyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (HMITFSI), 1-ethyl-3-methylimidazolium-fluorohydrogenate (EMI (FH) _2.3 F), N, N - Ethyl -N- methyl -N- (2-methoxyethyl) - tetrafluoroborate (DEMEBF _4), N, N- diethyl--N- methyl -N- (2-methoxyethyl) - bis (trifluoromethanesulfonyl) imide ( DEMETFSI), N-methyl-N-propylpiperidinium-bis (trifluoromethanesulfonyl) imide (PP13TFSI), triethylsulfonium-bis (trifluoromethanesulfonyl) imide (TESTFSI), N-methyl-Npropylpyrrolidinium-bis (Trifluoromethanesulfonyl) imide (P13TFSI), triethyloctylphosphonium-bis (trifluoromethanesulfonyl) imide (P2228TFSI), N-methyl-methoxymethylpyrrolidinium-tetrafluoroborate At least one may be selected from the group consisting of (C13BF ₄ ), lithium-bis (fluorosulfonyl) imide (LiFSI), and lithium-bis (trifluoromethanesulfonyl) imide (LiTFSI).
The reducing agent includes hydrazine, dimethylhydrazine, ascorbic acid, hydroquinone, sodium borohydride (NaBH ₄ ), tetrabutylammonium bromide (TBAB), LiAlH ₄ , ethylene glycol, polyethylene glycol, hydrogen iodide, and N, N At least one selected from the group consisting of diethylhydroxylamine.
In the electricity storage device including the electrode according to the present invention and the electrolyte, the electrode is made of the electrode material described above, thereby achieving the above-described object.
The electricity storage device may be an electric double layer capacitor, the electrolyte may be an ionic liquid, and the ionic liquid may be the same as the ionic liquid contained in the electrode material.
The electricity storage device is a lithium ion battery, the electrolyte is an ionic liquid containing lithium, and the ionic liquid containing lithium may be the same as the ionic liquid contained in the electrode material. .

An electrode material including a laminate in which reduced graphene oxide (RGO) according to the present invention is laminated contains an ionic liquid between RGOs. Since the ionic liquid is located between the RGOs, the laminate has a large specific surface area. As a result, the electrode material of the present invention can achieve a high energy density. In addition, since the surface free energy of RGO is reduced by positioning the ionic liquid on the surface of RGO, diffusion, adsorption and desorption of electrolyte, which is the same kind of ionic liquid, into RGO are promoted. Since the RGOs are separated by the ionic liquid, the ion diffusion path can be increased and the ion transport of the electrolyte can be promoted. As a result, when the electrode material of the present invention is used for an electrode of an electricity storage device in which the electrolyte is an ionic liquid, rate characteristics can be improved.

The method for producing an electrode material according to the present invention includes a step of preparing a suspension obtained by adding graphene oxide and an ionic liquid to a polar solvent, and a step of adding a reducing agent to the suspension and refluxing. By mixing graphene oxide and ionic liquid, the ionic liquid functions like a surfactant, suppresses the re-lamination of graphene oxide, and oxidizes while the ionic liquid is positioned between the graphene oxide in a self-organizing manner Graphene is stacked. Since the laminated body thus obtained may be reduced, one-pot synthesis is possible and a complicated apparatus is unnecessary, which is advantageous for industrial production.

Schematic diagram of the electrode material of the present invention The flowchart which shows the manufacturing process of the electrode material containing the laminated body of this invention The flowchart which shows the manufacturing process of the electrode material containing another laminated body of this invention Schematic diagram of an electric double layer capacitor provided with the electrode material of the present invention The figure which shows the SEM image of the product of Example 1 and Comparative Example 2 The figure which shows the TEM image of the product of Example 1 and Comparative Example 2 The figure which shows the Raman spectrum of the product of Example 1 and Comparative Example 2 The figure which shows the FT-IR spectrum of the product of Example 1 and Comparative Example 2 The figure which shows the nitrogen adsorption-and-desorption isotherm and pore diameter distribution of the product of Example 1 and Comparative Example 2 The figure which shows the specific capacity-voltage curve (CV curve) of the product of Example 1 and Comparative Example 2 The figure which shows the charging / discharging curve of the product of Example 1 and Comparative Example 2 The figure which shows the charging / discharging curve of the product of Examples 3-5 The figure which shows the current density dependence of the specific capacity of the product of Example 1 and Comparative Example 2 The figure which shows the Ragone plot of the product of Example 1 and Comparative Example 2 The figure which shows the cycling characteristics of the product of Example 1 and Comparative Example 2 The figure which shows the Nyquist plot of the product of Example 1 and Comparative Example 2 The figure which shows the frequency dependence of the normalized specific capacity of the product of Example 1 and Comparative Example 2

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same number is attached | subjected to the same element and the description is abbreviate | omitted.

(Embodiment 1)
In the first embodiment, an electrode material of the present invention and a manufacturing method thereof will be described.

FIG. 1 is a schematic view of the electrode material of the present invention.

The electrode material 100 of the present invention includes a stacked body 120 in which reduced graphene oxide 110 (referred to as RGO for simplicity) is integrated. The stacked body 120 contains an ionic liquid 130 between the RGOs 110. When the ionic liquid 130 is positioned between the RGOs 110, the RGO 110 is surely separated from the single layer, and thus the laminate 120 has a large specific surface area. Thereby, the electrode material 100 of this invention can achieve a high energy density. Further, since the ionic liquid 130 is positioned on the surface of the RGO 110, the surface free energy of the RGO 110 is reduced, so that the diffusion and adsorption / desorption of the electrolyte, which is the same kind of ionic liquid, to the RGO 110 is promoted. Furthermore, since the RGOs 110 are separated by the ionic liquid 130, the ion diffusion path can be increased and the ion transport of the electrolyte can be promoted. As a result, when the electrode material 100 of the present invention is used for an electrode of an electricity storage device in which the electrolyte is an ionic liquid, rate characteristics can be improved.

When the ionic liquid 130 is positioned between the RGOs 110, the RGOs are physically separated. The distance d is in the range of not less than 0.5 nm and not more than 2 nm, and facilitates diffusion of ions that are electrolytes.

RGO110 is obtained by removing the carbonyl group of graphene oxide, which is a nanosheet peeled off from graphite. RGO 110 has high conductivity since the carbonyl group is removed, and is suitable for an electrode material. On the other hand, since RGO110 has a hydroxy group, it has an affinity for a polar solvent or the like, and is advantageous for construction of an electricity storage device.

The RGO 110 preferably has a thickness of 0.3 nm to 1 nm, and has a sheet-like form having a length of 1 μm to 10 μm in the longitudinal direction. In the case of a sheet-like form having such a thickness, the graphite is substantially exfoliated, so that the specific surface area of the laminate 120 can be increased, so that an improvement in energy density can be expected.

The ionic liquid 130 is a salt composed of a combination of an anion and a cation, but is a liquid at room temperature, and has a characteristic of non-volatility because the vapor pressure is substantially zero. Examples of the anion include AlCl ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , I ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , NbF ₆ ⁻ , TaF ₆ ⁻ , F (HF) _{2. .3} ⁻ , p—CH ₃ PhSO ₃ ⁻ , CH ₃ CO ₂ ⁻ , CF ₃ CO ₂ ⁻ , CH ₃ SO ₃ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , C ₃ F ₇ CO ₂ ⁻ , C ₄ F ₉ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) (CF ₃ CO) N ⁻ , (CN ₂ N ^- etc. Examples of the cation include an imidazolium ion, a pyridinium ion, a piperidinium ion, a pyrrolidinium ion, and a sulfonium ion having an alkyl group having 1 to 8 carbon atoms.

More specifically, the ionic liquid 130 includes 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF ₄ ), 1-ethyl-3-methylimidazolium-bis (fluorosulfonyl) imide (EMIFSI), 1- Ethyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (EMITFSI), 1-butyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (BMITSI), 1-hexyl-3-methylimidazolium tetra tetrafluoroborate (HMIBF _4), 1- hexyl-3-methylimidazolium - bis (trifluoromethanesulfonyl) imide (HMITFSI), 1- ethyl-3-methylimidazolium - fluorohydrocarbon oxygenate (EMI (FH) _.3 F), N, N- diethyl--N- methyl -N- (2-methoxyethyl) - tetrafluoroborate (DEMEBF _4), N, N- diethyl--N- methyl -N- (2-methoxyethyl) -Bis (trifluoromethanesulfonyl) imide (DEMETFSI), N-methyl-N-propylpiperidinium-bis (trifluoromethanesulfonyl) imide (PP13TFSI), triethylsulfonium-bis (trifluoromethanesulfonyl) imide (TESTFSI), N- Methyl-Npropylpyrrolidinium-bis (trifluoromethanesulfonyl) imide (P13TFSI), triethyloctylphosphonium-bis (trifluoromethanesulfonyl) imide (P2228TFSI), N-methyl-methoxymethylpyrrolidinium-te At least one selected from the group consisting of trifluoroborate (C13BF ₄ ), lithium-bis (fluorosulfonyl) imide (LiFSI), and lithium-bis (trifluoromethanesulfonyl) imide (LiTFSI). Since these ionic liquids are available and can be used as an electrolyte for an electricity storage device, they can be used for the electrode material of the present invention.

In the laminate 120, the ratio of the ionic liquid 130 to the RGO 110 (weight ratio, hereinafter simply referred to as the ratio of RGO and ionic liquid) is preferably 0.01 or more and 1.00 or less. If the ratio is less than 0.01, since the ionic liquid 130 is small, the RGO 110 may re-stack without supporting the ionic liquid, and the specific surface area may not be increased. Further, since there are few ionic liquids 130 located in the RGO 110, the surface free energy of the RGO 110 cannot be reduced, so that the adsorption / desorption / diffusion of the ionic liquid as the electrolyte cannot be promoted. When the ratio exceeds 1.00, the ionic liquid 130 is excessively present between the RGOs, and the ionic liquid as an electrolyte may not be able to diffuse into the laminate 120.

In the laminated body 120, the ratio of the RGO 110 and the ionic liquid 130 is more preferably 0.02 or more and 0.60 or less. Thereby, the diffusion to the laminated body 120 of the ionic liquid which is electrolyte can be accelerated | stimulated reliably.

In the stacked body 120, for example, when the ionic liquid 130 is EMIMBF ₄ , the ratio of the RGO 110 and the ionic liquid 130 is more preferably 0.02 or more and 0.15 or less. Thereby, the diffusion of the ionic liquid, which is an electrolyte, into the laminate 120 can be surely promoted, and a high specific capacity can be maintained even at a high current density, and the retention characteristics can be excellent.

The specific surface area obtained by the BET method of the laminate 120 is preferably in the range of 350 m ² / g to 500 m ² / g. If the specific surface area is less than 350 m ² / g, the ionic liquid is not sufficiently located between the RGOs, the RGO is not separated from the single layer, or the ionic liquid is located excessively between the RGOs. High energy density and high rate characteristics cannot be obtained. When the specific surface area exceeds 500 m ² / g, the RGO is peeled off in a single layer, but the ionic liquid may not be positioned between the RGOs, and the electrolyte may not be used as an electrode material for an electricity storage device that is an ionic liquid. is there.

The specific surface area obtained by the BET method of the laminate 120 is more preferably in the range of 420 m ² / g to 450 m ² / g. If this range is satisfied, the graphene is peeled off in a single layer, and it can be considered that the ionic liquid is arranged between the layers at the ratio of RGO and ionic liquid described above, so that high energy density and high rate characteristics are ensured. To do.

The pore volume determined by the BJH method of the laminate 120 is preferably in the range of 0.75 cc / g to 1.5 cc / g. When the pore volume is less than 0.75 cc / g, a sufficient amount of the ionic liquid as the electrolyte cannot be diffused into the laminate 120, so that a high energy density cannot be achieved. Although the pore volume may exceed 1.5 cc / g, it is difficult to produce a high-quality laminate in which RGOs in which an ionic liquid is located are laminated between RGOs. The pore volume determined by the BJH method of the laminate 120 is more preferably in the range of 0.85 cc / g or more and 0.95 cc / g or less. If this range is satisfied, the ionic liquid is disposed between the layers at the ratio of the RGO and the ionic liquid described above, and a sufficient amount of ionic liquid as an electrolyte enters the layers, resulting in high energy density and high Ensure rate characteristics.

The laminate 120 has pores having two different pore sizes. Specifically, the laminate 120 preferably has mesopores having a diameter in the range of 2 nm to 6 nm and macropores having a diameter of 50 nm or more. With such a structure, when the electrode material 100 of the present invention is employed in an electricity storage device in which the electrolyte is an ionic liquid, ions can be adsorbed in the mesopores, and the ionic liquid can be retained in the macropores. . That is, since the ion diffusion distance can be shortened by applying an electric field, high rate characteristics can be achieved.

The laminate 120 preferably has a specific capacity in the range of 80 F / g to 140 F / g at a current density of 20 A / g. That is, since the laminate 120 of the present invention has a high specific capacity even at a high current density, it has excellent retention characteristics and is advantageous for an electrode material.

The electrode material 100 of the present invention may consist of a laminate 120, but may contain a binder, an organic solvent, a conductive agent, a supporting salt, etc. in addition to the laminate 120 as long as the electrical characteristics are maintained. For example, the electrode material 100 may include a binder such as a fluororesin such as polytetrafluoroethylene (PTFE) in addition to the laminate 120, and may be molded into a pellet shape or a sheet shape. For example, when the electrode material 100 is applied to an electrode of a lithium ion battery, the electrode material 100 may include a supporting salt in addition to the stacked body 120. For example, the electrode material 100 may include a conductive agent in addition to the stacked body 120 to enhance conductivity.

Next, a method for producing an electrode material including the laminate of the present invention will be described.

FIG. 2 is a flowchart showing a manufacturing process of an electrode material including the laminate of the present invention. Each step will be described in detail.

Step S210: A suspension obtained by adding graphene oxide (hereinafter referred to as GO for simplicity) and an ionic liquid to a polar solvent is prepared and stirred. By mixing and stirring the GO and the ionic liquid, the ionic liquid functions like a surfactant in the prepared suspension, and the GO is laminated while the ionic liquid is positioned between the layers in a self-organizing manner. .

GO may be purchased or may be produced from graphite by the Brodie method, the Staudenmeier method, the Hummer method, the modified Hummers method, or the like. The graphene oxide preferably has a sheet-like form having a thickness of 0.3 nm to 1 nm and a length of 1 μm to 10 μm in the longitudinal direction. In such a sheet-like form, since the graphite is substantially exfoliated, the specific surface area of the resulting laminate is increased, and an improvement in energy density can be expected.

The polar solvent is selected from the group consisting of water, dimethyl sulfoxide (DMSO), N, N-dimethylsulfamide (DMF) and ethanol. Since these polar solvents have an affinity for the ionic liquid described later, a good suspension can be obtained. For example, when a solution containing GO in a polar solvent is prepared, the concentration of the solution is preferably 0.5 mg / mL or more and 3 mg / mL or less. If it is this range, lamination | stacking of GO in which the ionic liquid was located between layers may be accelerated | stimulated.

The ionic liquid is the same as the ionic liquid 130 described with reference to FIG. 1, but is a salt composed of a combination of an anion and a cation, but is a liquid at room temperature and has a substantially zero vapor pressure. It has the feature of non-volatility. Examples of the anion include AlCl ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , I ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , NbF ₆ ⁻ , TaF ₆ ⁻ , F (HF) _{2. .3} ⁻ , p—CH ₃ PhSO ₃ ⁻ , CH ₃ CO ₂ ⁻ , CF ₃ CO ₂ ⁻ , CH ₃ SO ₃ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , C ₃ F ₇ CO ₂ ⁻ , C ₄ F ₉ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) (CF ₃ CO) N ⁻ , (CN ₂ N ^- etc. Examples of the cation include an imidazolium ion, a pyridinium ion, a piperidinium ion, a pyrrolidinium ion, and a sulfonium ion having an alkyl group having 1 to 8 carbon atoms.

More specifically, the ionic liquids are 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF ₄ ), 1-ethyl-3-methylimidazolium-bis (fluorosulfonyl) imide (EMIFSI), 1-ethyl -3-Methylimidazolium-bis (trifluoromethanesulfonyl) imide (EMITFSI), 1-butyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (BMITSI), 1-hexyl-3-methylimidazolium tetrafluoro borate (HMIBF _4), 1- hexyl-3-methylimidazolium - bis (trifluoromethanesulfonyl) imide (HMITFSI), 1- ethyl-3-methylimidazolium - fluorohydrocarbon oxygenate (EMI _{(FH) 2.3} ), N, N-diethyl -N- methyl -N- (2-methoxyethyl) - tetrafluoroborate (DEMEBF _4), N, N- diethyl--N- methyl -N- (2-methoxyethyl) - bis ( Trifluoromethanesulfonyl) imide (DEMETFSI), N-methyl-N-propylpiperidinium-bis (trifluoromethanesulfonyl) imide (PP13TFSI), triethylsulfonium-bis (trifluoromethanesulfonyl) imide (TESTFSI), N-methyl-N Propylpyrrolidinium-bis (trifluoromethanesulfonyl) imide (P13TFSI), Triethyloctylphosphonium-bis (trifluoromethanesulfonyl) imide (P2228TFSI), N-methyl-methoxymethylpyrrolidinium-tetraf At least one selected from the group consisting of fluoroborate (C13BF ₄ ), lithium-bis (fluorosulfonyl) imide (LiFSI), and lithium-bis (trifluoromethanesulfonyl) imide (LiTFSI). These ionic liquids are preferred because they are available and have an affinity for the polar solvents described above.

The ratio of the ionic liquid to GO (weight ratio, hereinafter simply referred to as the ratio of GO to ionic liquid) is preferably 0.005 or more and 0.5 or less. When the ratio is less than 0.05, since the ionic liquid is small, the GO may not be re-laminated without supporting the ionic liquid and the specific surface area may not be increased. Moreover, since there are few ionic liquids located in GO, the surface free energy of GO cannot be made small, Therefore The adsorption / desorption / diffusion of the ionic liquid which is electrolyte cannot be promoted. If the ratio exceeds 0.5, there may be an excess of ionic liquid between the GOs, and the ionic liquid that is an electrolyte may not diffuse into the laminate. The specific gravity of the ionic liquid described above is in the range of 1.1 g / mL to 1.6 g / mL. Therefore, even if the ratio of GO to ionic liquid is calculated by weight ratio, the type of ionic liquid There is virtually no dependency.

The ratio of GO to ionic liquid is more preferably 0.01 or more and 0.3 or less. Thereby, the spreading | diffusion to the laminated body of the ionic liquid which is electrolyte can be accelerated | stimulated reliably.

For example, when the ionic liquid is EMIMBF ₄ , the ratio of GO to the ionic liquid is more preferably 0.01 or more and 0.07 or less. As a result, diffusion of the ionic liquid, which is an electrolyte, into the laminate can be surely promoted, a high specific capacity can be maintained even at a high current density, and the retention characteristics can be excellent.

Step S220: A reducing agent is added to the suspension obtained in step S210 and refluxed. As a result, in the suspension obtained in step S210, GO in the stacked body in which GO is stacked with the ionic liquid positioned between the layers is reduced to become reduced graphene oxide (referred to as RGO). .

Reducing agents include hydrazine, dimethylhydrazine, ascorbic acid, hydroquinone, sodium borohydride (NaBH ₄ ), tetrabutylammonium bromide (TBAB), LiAlH ₄ , ethylene glycol, polyethylene glycol, hydrogen iodide, and N, N— At least one selected from the group consisting of diethylhydroxylamine. With these reducing agents, the reduction of GO is promoted and RGO is obtained.

Reflux time is preferably in the range of 1 hour to 10 hours. If the reflux time is less than 1 hour, the reduction does not proceed and part or all of GO becomes unreacted. Even if the reflux time exceeds 10 hours, the reduction does not proceed any more, so it is meaningless.

In addition, following step S220, the product may be washed with water and dried in an oven or the like.

As described above, according to the manufacturing method of the present invention shown in FIG. 2, it is only necessary to reduce the laminated body made of GO with the ionic liquid positioned between the layers, so that one-pot synthesis is possible and a complicated apparatus is not required. So it is advantageous for industrial production.

FIG. 3 is a flowchart showing a manufacturing process of an electrode material including another laminate of the present invention.

Step S310: A suspension to which graphene oxide (RGO) reduced to a polar solvent and an ionic liquid are added is prepared and stirred. By mixing and stirring the RGO and the ionic liquid, the ionic liquid functions like a surfactant in the prepared suspension, and the RGO is laminated while the ionic liquid is positioned between the RGOs in a self-organizing manner. To do.

RGO preferably has a sheet-like form having a thickness of 0.3 nm to 1 nm and a length of 1 μm to 10 μm in the longitudinal direction. In such a sheet-like form, since the graphite is substantially exfoliated, the specific surface area of the resulting laminate is increased, and an improvement in energy density can be expected.

The ratio (weight ratio) between RGO and ionic liquid is preferably 0.01 or more and 1.00 or less. If the ratio is less than 0.01, since there is little ionic liquid, RGO may re-stack without supporting the ionic liquid, and the specific surface area may not be increased. Moreover, since there are few ionic liquids located in RGO, the surface free energy of RGO cannot be made small, Therefore The adsorption / desorption / diffusion of the ionic liquid which is electrolyte cannot be promoted. When the ratio exceeds 1.00, an ionic liquid is excessively present between RGOs, and the ionic liquid as an electrolyte may not be able to diffuse into the laminate.

The ratio of RGO and ionic liquid is more preferably 0.02 or more and 0.60 or less. Thereby, the spreading | diffusion to the laminated body of the ionic liquid which is electrolyte can be accelerated | stimulated reliably.

In step S310, since the polar solvent and the ionic liquid are the same as those of the polar solvent and the ionic liquid in step S210, the description thereof is omitted. Further, following step S310, the product may be washed with water and dried in an oven or the like.

As described above, according to the manufacturing method of the present invention shown in FIG. 3, there is no need to reduce, so that it is effective when RGO is obtained in advance.

(Embodiment 2)
In Embodiment 2, an application using an electrode material including the laminate of the present invention obtained in Embodiment 1 will be described.

FIG. 4 is a schematic diagram of an electric double layer capacitor provided with the electrode material of the present invention.

The electric double layer capacitor of the present invention includes at least an electrode and an electrolyte. In the electric double layer capacitor 400 of FIG. 4, a positive electrode 410 and a negative electrode 420 are immersed in an electrolyte 430 as electrodes. The positive electrode 410 and the negative electrode 420 are made of the electrode material 100 described in the first embodiment. The electrolyte 430 is an ionic liquid. The ionic liquid is the same as the ionic liquid described in Embodiment 1, but preferably, the ionic liquid of the electrolyte 430 and the ionic liquid contained in the positive electrode 410 and the negative electrode 420 are the same. Thereby, since diffusion of electrolyte 430 to positive electrode 410 and negative electrode 420 is promoted, high rate characteristics can be achieved.

The electric double layer capacitor 400 further includes a separator 440 between the positive electrode 410 and the negative electrode 420 to isolate the positive electrode 410 and the negative electrode 420.

The material of the separator 440 is, for example, fluoropolymer, polyether such as polyethylene oxide or polypropylene oxide, polyolefin such as polyethylene or polypropylene, polyacrylonitrile, polyvinylidene chloride, polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylo It is a material selected from nitrile, polyvinyl acetate, polyvinyl pyrrolidone, polyethyleneimine, polybutadiene, polystyrene, polyisoprene, polyurethane polymers and derivatives thereof, cellulose, paper, and nonwoven fabric.

In the electric double layer capacitor 400, the positive electrode 410, the negative electrode 420, the electrolyte 430, and the separator 440 described above are accommodated in the cell 450. Further, each of the positive electrode 410 and the negative electrode 420 may have an existing current collector.

Such an electric double layer capacitor 400 may be a chip type, a coin type, a mold type, a pouch type, a laminate type, a cylindrical type, a square type or the like, and is used in a module in which a plurality of these are connected. May be.

Next, the operation of the electric double layer capacitor 400 of FIG. 4 will be described.

When a voltage is applied to the electric double layer capacitor 400, the anion of the ionic liquid that is the electrolyte 430 is adsorbed on the positive electrode 410, and the cation of the ionic liquid that is the electrolyte 430 is adsorbed on the negative electrode 420, respectively. As a result, an electric double layer is formed on the surface of each of the positive electrode 410 and the negative electrode 420 and is charged. Here, since the positive electrode 410 and the negative electrode 420 are formed from the electrode material described in Embodiment 1, adsorption and diffusion of cations and anions are facilitated, and high rate characteristics can be achieved. In addition, since the positive electrode 410 and the negative electrode 420 are formed from the electrode material described in Embodiment 1, many ions can be adsorbed on a large specific surface area and high energy density can be achieved.

When the charged electric double layer capacitor 400 is connected to a circuit such as a resistor, the anions and cations adsorbed on the positive electrode 410 and the negative electrode 420 are desorbed and discharged. Again, since the positive electrode 410 and the negative electrode 420 are formed from the electrode materials described in the first embodiment, desorption / diffusion of cations and anions is facilitated, and high rate characteristics can be achieved. Moreover, since it is excellent in electroconductivity, output density can also be improved with ease of desorption / diffusion.

Thus, since the electric double layer capacitor 400 of the present invention uses the electrode material of the present invention, it enables quick charging and has a high energy density and a high output density. Moreover, since the formation of an electric double layer is used for charging / discharging, it is excellent in repeated use. The electric double layer capacitor 400 of the present invention can be used for wind power generation, electric vehicles and the like.

The electrode material of the present invention may be applied to a lithium ion battery. In this case, the lithium ion battery of the present invention includes at least an electrode and an electrolyte, as in the electric double layer capacitor 400 of the present invention of FIG. 4, but the positive electrode 410 has at least an active material capable of adsorbing and desorbing lithium ions. The content is different.

The positive electrode 410 is typically represented by LiMO ₂ (M is an element selected from the group consisting of Ni, Co, Mn, Fe, Ti, Zr, Al, Mg, Cr, and V). Li metal oxide is known, but a material for a positive electrode applied to an existing lithium ion battery is applied. Alternatively, the electrode material of the present invention coated with Li metal may be used as the positive electrode 410.

Next, the operating principle of the lithium ion battery will be briefly described.

When a voltage is applied to the lithium ion battery, Li is ionized from the positive electrode, and is adsorbed and accumulated on the negative electrode. Here, since the negative electrode is made of the electrode material of the present invention, the diffusion of Li ions is promoted, so that a high energy density can be achieved with a large specific surface area and a large pore volume while achieving high rate characteristics. In this way, the lithium ion battery is charged.

On the other hand, when a lithium ion battery is connected to a circuit such as a resistor, Li ions accumulated and adsorbed on the negative electrode move to the positive electrode side and return to the positive electrode. Again, since the negative electrode is formed from the electrode material described in Embodiment 1, lithium ion desorption / diffusion is facilitated, and high rate characteristics can be achieved. Moreover, since it is excellent in electroconductivity, output density can also be improved with ease of desorption / diffusion. In this way, the lithium ion battery is discharged.

Thus, since the lithium ion battery of the present invention uses the electrode material of the present invention, it can be charged quickly and has a high energy density and a high output density. The lithium ion battery of the present invention can be used in portable electronic devices such as notebook computers and mobile phones.

Next, the present invention will be described in detail using specific examples, but it should be noted that the present invention is not limited to these examples.

[Example 1]
In Example 1, an electrode material containing 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF ₄ ) as an ionic liquid was produced in a laminate in which reduced graphene oxide (RGO) was laminated.

First, graphene oxide was produced from natural graphite powder using the modified Hummers method. The graphite powder was mixed with sulfuric acid and sodium nitrate in an ice bath. After these mixtures were stirred, sodium permanganate was slowly added so that the temperature did not exceed 20 ° C. These mixtures were reacted in a 35 ° C. water bath for 1 hour. Thereby, the mixture became a paste.

Deionized water was slowly added to this paste-like mixture, and the mixture was further stirred for 1 hour. Next, water was further added to the mixture, and after stirring for 30 minutes, hydrogen peroxide was added. This resulted in a dark brown mixture becoming a yellow suspension.

The yellow suspension was centrifuged and the resulting solid was washed 6 times with hydrochloric acid solution and deionized water to remove metal ions and acid and dried in vacuum. Thus, graphene oxide (GO) was obtained.

Next, the electrode material of the present invention was manufactured using GO. A suspension was prepared by adding GO to water as a polar solvent and EMIMBF ₄ as an ionic liquid (step S210 in FIG. 2). Specifically, powdered GO is dispersed in water and subjected to ultrasonic treatment for 2 hours to prepare a 1 mg / mL uniform GO aqueous solution, and EMIMBF ₄ (0.5 mL) is added as an ionic liquid to this GO aqueous solution (100 mL). ) And stirred for 30 minutes to obtain a suspension.

Next, the suspension was heated to 98 ° C., hydrazine (35 wt%, 0.1 mL) was added as a reducing agent, and the mixture was refluxed at 98 ° C. for 2 hours (step S220 in FIG. 2). The resulting product was washed with water and dried in an oven at 60 ° C.

The morphology and structure of the product thus obtained were analyzed with a scanning electron microscope (SEM, JSM-6500 manufactured by JEOL Ltd.) and a transmission electron microscope (TEM, EMM-2100 manufactured by JEOL Ltd.). And observed. These results are shown in FIGS. 5C and 5D and FIGS. 6C and 6D.

In addition, the porous structure of the product was evaluated by a Raman spectroscopic apparatus (RAMAN-11 manufactured by Nanophoton Co., Ltd.) using Raman spectroscopy. The wavelength of the light source was 532 nm. The results are shown in FIG. The presence of an ionic liquid in the product was measured by a Fourier transform infrared spectrometer (FT-IR, Thermo Fisher Scientific, Inc. Nicolet 6700) using Fourier transform infrared spectroscopy. The results are shown in FIG.

The specific surface area and pore distribution of the product were measured by the BET method. For the measurement, an Autosorb-iQ analyzer manufactured by Quantachrome Corporation was used. The results are shown in FIG. The specific surface area and pore volume were calculated based on the amount of adsorption in the relative pressure (P / P ₀ ) range of 0.05 to 0.3. The results are shown in Table 2.

Next, in order to evaluate the electrical characteristics of the product, an electric double layer capacitor (supercapacitor) using the product as an electrode was manufactured. The specific manufacturing procedure was as follows. The product (90 wt%) and polytetrafluoroethylene (PTFE, 10 wt%) were dispersed in ethanol and sonicated to obtain a suspension. The suspension was passed through a porous membrane by vacuum filtration. This porous membrane was dried in vacuum for 24 hours, and the membrane made of the product obtained by vacuum filtration and PTFE was cut into a circle, and this was used as an electrode. The electrode was circular with a diameter of 15 mm and weighed about 1 mg. Next, a porous separator (440 in FIG. 4) is placed between these electrodes (410 and 420 in FIG. 4) in a stainless steel cell (450 in FIG. 4), and EMIMBF ₄ (430 in FIG. 4) is used as an electrolyte. ) To manufacture an electric double layer capacitor (400 in FIG. 4). The electric double layer capacitor was assembled in a glove box filled with Ar gas.

Electrochemical measurement of the electric double layer capacitor was performed using a multi-channel potentiostat galvanostat (manufactured by Bio-Logic, VMP-300). Specific capacity-voltage measurement (CV measurement) and galvanostat charge / discharge measurement were performed in a potential range of 0 V to 3.5 V at room temperature. The results are shown in FIG. 10 and FIG.

Specific capacity Cs (F / g) was calculated according to the formula Cs = 4I / (mdV / dt). Here, I (A) is a constant current, m (g) is the total weight of the two electrodes, and dV / dt (V / s) is Vmax (voltage at the start of discharge) and 1/2 Vmax. Is a slope obtained by linear fitting of the discharge curve. The results are shown in FIG. 13, Table 3 and Table 4.

In order to examine the superiority of the electric double layer capacitor, a Ragone plot was created. A longitudinal axis of the Ragone plots energy density _E cell (Wh / kg) was calculated according to the equation _E cell = ^CsV 2/8. The power density P _cell (W / kg), which is the horizontal axis of the Ragone plot, was calculated according to the formula P _cell = E _cell / t (where t is the discharge time). The results are shown in FIG.

Next, the cycle characteristics of the electric double layer capacitor were examined. The charge / discharge of the electric double layer capacitor was repeated up to 2000 times, and after each charge / discharge cycle, the change in specific capacity at a current density of 10 A / g was measured. The results are shown in FIG.

Electrochemical impedance spectroscopy (EIS) measurement was performed using an electric double layer capacitor. Measurements were made over a frequency range of 100 kHz to 10 mHz at an open circuit potential with an AC amplitude of 5 mV. The resulting impedance was Nyquist plotted. The results are shown in FIG. From the frequency response analysis of FIG. 16, based on the RC equivalent circuit, the capacitance C is expressed by the equation C = −1 / (2πfZ ″) (where f is the frequency (Hz) and Z ″ is the imaginary part of the impedance. The frequency dependence of the capacity was examined. The results are shown in FIG.

[Comparative Example 2]
In Comparative Example 2, an electrode material containing a laminate in which reduced graphene oxide (RGO) was laminated without using an ionic liquid was manufactured. The same as Example 1 except that no ionic liquid was used.

As in Example 1, the morphology and structure of the product obtained in Comparative Example 2 were observed using SEM and TEM. The results are shown in FIGS. 5 (a) and 5 (b) and FIGS. 6 (a) and 6 (b). As in Example 1, the product obtained in Comparative Example 2 was evaluated by Raman spectroscopy and Fourier transform infrared spectroscopy. The results are shown in FIG. 7 and FIG. Furthermore, the specific surface area and pore distribution of the product obtained in Comparative Example 2 were measured, and the specific surface area and pore volume were calculated. The results are shown in FIG.

Similarly to Example 1, an electric double layer capacitor (supercapacitor) using the product obtained in Comparative Example 2 as an electrode was manufactured, CV measurement and galvanostat charge / discharge measurement were performed, and the specific capacity depends on the current density. Sex was calculated. The results are shown in FIG. 10, FIG. 11, FIG. 13, Table 3 and Table 4. Further, a Ragone plot of the electric double layer capacitor manufactured in Comparative Example 2 was created, cycle characteristics were measured, and EIS measurement was performed. The results are shown in FIGS.

[Example 3]
In Example 3, as in Example 1, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF ₄ ) is contained as an ionic liquid in a laminate in which reduced graphene oxide (RGO) is laminated. An electrode material was manufactured. However, it was the same as Example 1 except using 500 mL of GO aqueous solution (1 mg / mL).

In the same manner as in Example 1, the morphology and structure of the product obtained in Example 3 were observed, and the specific surface area and pore distribution were measured. Further, as in Example 1, an electric double layer capacitor (supercapacitor) using the product obtained in Example 3 as an electrode was manufactured, CV measurement and galvanostat charge / discharge measurement were performed, and a Ragone plot, cycle The characteristics were measured and EIS measurement was performed. Here, the result of the galvanostat charge / discharge measurement is shown in FIG.

[Example 4]
In Example 4, as in Example 1, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF ₄ ) is contained as an ionic liquid in a laminate in which reduced graphene oxide (RGO) is laminated. An electrode material was manufactured. However, it was the same as Example 1 except that 2 mL of EMIMBF ₄ was used.

In the same manner as in Example 1, the morphology and structure of the product obtained in Example 4 were observed, and the specific surface area and pore distribution were measured. Further, as in Example 1, an electric double layer capacitor (supercapacitor) using the product obtained in Example 3 as an electrode was manufactured, CV measurement and galvanostat charge / discharge measurement were performed, and a Ragone plot, cycle The characteristics were measured and EIS measurement was performed. Here, the result of the galvanostat charge / discharge measurement is shown in FIG.

[Example 5]
In Example 5, as in Example 1, 1-ethyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (EMITFSI) was used as an ionic liquid in a laminate in which reduced graphene oxide (RGO) was laminated. ) Was produced. However, it was the same as Example 1 except that 0.5 mL of EMITFSI was used as the ionic liquid.

As in Example 1, the morphology and structure of the product obtained in Example 5 were observed, and the specific surface area and pore distribution were measured. Similarly to Example 1, the product obtained in Example 3 was used as an electrode, EMITFSI was used as an electrolyte, an electric double layer capacitor (supercapacitor) was manufactured, and CV measurement and galvanostat charge / discharge measurement were performed. The Rone plot and cycle characteristics were measured, and EIS measurement was performed. Here, the result of the galvanostat charge / discharge measurement is shown in FIG.

Table 1 shows a list of experimental conditions for the above examples and comparative examples for simplicity. In addition, the weight of the ionic liquid used for the electrode material of the present invention was calculated assuming that the specific gravity of EMIMBF ₄ and EMITFSI was 1.294 g / ml and 1.53 g / ml, respectively. Further, when GO was reduced to RGO, the weight of RGO was calculated based on being 1/2 of the weight of GO.

FIG. 5 is a diagram showing SEM images of the products of Example 1 and Comparative Example 2.

The SEM image was taken at an acceleration voltage of 15 kV. 5 (a) and 5 (b) are SEM images of the product of Comparative Example 2, and FIGS. 5 (c) and 5 (d) are SEM images of the product of Example 1. FIG. According to FIGS. 5 (a) and (b), the product of Comparative Example 2 was tightly packed and did not exhibit a porous structure. On the other hand, according to FIGS. 5 (c) and (d), the product of Example 1 represented a porous structure consisting of a layered curved sheet. From this, the product of Example 1 can adsorb many ions that are electrolytes on the surface, suggesting an increase in energy density. Although not shown, the products of Examples 3 to 5 also showed the same morphology as Example 1.

FIG. 6 is a diagram showing TEM images of the products of Example 1 and Comparative Example 2.

6 (a) and 6 (b) are TEM images of the product of Comparative Example 2, and FIGS. 6 (c) and 6 (d) are TEM images of the product of Example 1. FIG. According to FIGS. 6 (a) and (b), the product of Comparative Example 2 showed a flat state in which a large number of large RGO sheets were laminated. On the other hand, according to FIGS. 6C and 6D, the product of Example 1 is similar to the SEM image, although the layered curved RGO sheets are laminated, compared with that of Comparative Example 2. It turned out to be very thin. For example, FIG. 6D shows that the thin RGO sheet 620 is positioned above the RGO sheet 610, and each RGO sheet is laminated in a single-layer peeled state. Although not shown, the products of Examples 3 to 5 also showed the same morphology as Example 1.

As described above, in the method described with reference to FIG. 2, by using the ionic liquid, the ionic liquid functions as a surfactant or a soft template, and maintains the state where the RGO is peeled off from the single layer while maintaining the state where the RGO is separated from the interlayer. It was confirmed that a laminate composed of RGO holding the liquid was obtained.

FIG. 7 is a diagram showing the Raman spectra of the products of Example 1 and Comparative Example 2.

Raman spectra of any of the products also, D band at 1340 cm ^-1, and showed two prominent peaks of G band at 1590 cm ^-1. The G band corresponds to an E _2g phonon of C _sp2 atoms, and the D band corresponds to a strain resulting from structural defects. The intensity ratio of the D band to the G band (I _D / I _G ) is known as an indicator of the degree of distortion, and the I _D / I _G (1.53) of the product of Example 1 is Greater than that of the product (1.30). This is because the product of Example 1 is more distorted than the product of Comparative Example 2, which is consistent with the results of FIGS. Although not shown, the I _D / I _G of the products of Examples 3 to 5 were also larger than that of the product of Comparative Example 2.

FIG. 8 is a diagram showing FT-IR spectra of the products of Example 1 and Comparative Example 2.

When the FI-IR spectra of the product of Example 1 and the product of Comparative Example 2 are compared, the FT-IR spectrum of the product of Example 1 has wave numbers of 3160 cm ⁻¹ , 3090 cm ⁻¹ , 1572 cm ⁻¹ and 1065 cm. ^A noticeable peak different from that of the product of Comparative Example 2 was observed at ^-1 . These peaks, CH _x unsaturated bond, C-N bond from imidazolium ring, and, _[BF 4] ^- corresponding to stretching vibration of BF binding anions. This indicates that the product of Example 1 has an ionic liquid located on the surface of RGO. Although not shown, the products of Examples 3 to 4 also showed the same spectrum as the FT-IR spectrum of the product of Example 1.

From the above, it was confirmed that the product of the present invention was a material including a laminate in which RGO containing an ionic liquid was laminated. Furthermore, when the manufacturing method (FIG. 2) of this invention was used, it turned out that the material containing the laminated body which the RGO containing the above-mentioned ionic liquid laminated | stacked is obtained.

FIG. 9 is a graph showing nitrogen adsorption / desorption isotherms and pore size distributions of the products of Example 1 and Comparative Example 2.

FIG. 9 (a) shows a nitrogen adsorption / desorption isotherm, that of the product of Comparative Example 2 is of type IV indicating that mesopores are present, that of the product of Example 1 is mesopores And the combination of type III and IV indicating the presence of macropores. From comparison between Example 1 and Comparative Example 2, it can be seen that the macropores were generated by the ionic liquid. This result is in good agreement with the results of FIGS. 5 and 6 (the product of Example 1 exhibits a porous structure). Although not shown, the nitrogen adsorption and desorption isotherms of the products of Examples 3-5 also showed a combination of types III and IV.

Since the material of the present invention has mesopores and macropores, when the material of the present invention is employed in an electricity storage device in which the electrolyte is an ionic liquid, ions can be adsorbed into the mesopores, Since the ionic liquid that is an electrolyte can be retained, the ion diffusion distance can be shortened, and thus high rate characteristics can be achieved.

FIG. 9 (b) shows the pore size distribution. It was found that the pore peak of the product of Example 1 is at 4 nm and mainly has mesopores having a diameter in the range of 2 nm to 6 nm. On the other hand, the pore peak of the product of Comparative Example 2 was at 3.5 nm, which was smaller than that of the product of Example 1. This indicates that the RGO in the product of Example 1 is more monolayer separated than that in the product of Comparative Example 2 due to the function of the ionic liquid as a surfactant. Table 2 shows the specific surface area and pore volume calculated from FIG.

According to Table 2, it can be seen that the specific surface area and pore volume of the product of Example 1 are larger than that of the product of Comparative Example 2. In particular, it is suggested that the material of the present invention achieves a high energy density by having a large specific surface area.

FIG. 10 is a diagram showing specific capacity-voltage curves (CV curves) of the products of Example 1 and Comparative Example 2.

FIGS. 10 (a) and 10 (b) show the results of the sweep rates of 50 mV / s and 500 mV / S, respectively. According to FIG. 10 (a), the products of Example 1 and Comparative Example 2 exhibited a rectangular CV curve representing an ideal electric double layer capacitor. However, as shown in FIG. 10 (b), when the sweep rate was increased, the product of Example 1 exhibited a rectangular CV curve, whereas the product of Comparative Example 2 did not exhibit a rectangular CV curve. It was. From this, it was confirmed that the product of Example 1 functions as an electrode material having excellent rate characteristics. Although not shown, the CV curves of the products of Examples 3-5 showed similar results to those of the product of Example 1.

FIG. 11 is a diagram showing charge / discharge curves of the products of Example 1 and Comparative Example 2.
FIG. 12 shows the charge / discharge curves of the products of Examples 3 to 5.

FIGS. 11A and 11B are constant current charge / discharge curves with current densities of 2 A / g and 20 A / g, respectively. FIG. 12 is a constant current charge / discharge curve with a current density of 20 A / g. In all results, the product showed a constant current charge / discharge curve typical of an electric double layer capacitor. Specifically, according to FIG. 11 (a), at a low current density, the charge / discharge curve of the product of Example 1 is substantially longer than that of Comparative Example 2, although the discharge time is slightly longer. It didn't change. However, according to FIG. 11B, when the current density increased, the discharge time of the charge / discharge curve of the product of Example 1 was significantly longer than that of Comparative Example 2. According to FIG. 12, similar to the product of Example 1, the products of Examples 3-5 showed similar results with long discharge times. From this, it was confirmed that the products of Examples 1, 3 to 5 function as electrode materials having excellent rate characteristics.

FIG. 13 is a graph showing the current density dependence of the specific capacities of the products of Example 1 and Comparative Example 2.

It was found that the specific capacity of the product of Example 1 did not substantially change regardless of the current density. On the other hand, the specific capacity of the product of Comparative Example 2 decreased as the current density increased. Table 3 summarizes specific capacity values at each current density.

According to Table 3, the specific capacity of the product of Example 1 at a current density of 0.5 A / g is 135 F / g, slightly larger than that of the product of Comparative Example 2 (129 F / g). It was. This is because the specific surface area of the product of Example 1 is larger than that of the product of Comparative Example 2 as described with reference to Table 2.

Furthermore, according to Table 3, the specific capacity of the product of Example 1 at a current density of 20 A / g was 114 F / g, whereas that of the product of Comparative Example 2 was 68 F / g. The specific capacity of the product of Comparative Example 2 decreased from 129 F / g (@ 0.5 A / g) to 68 F / g (@ 20 A / g), and its retention rate was only 53%, with very low retention It was a characteristic. On the other hand, the specific capacity of the product of Example 1 slightly decreased from 135 F / g (@ 0.5 A / g) to 114 F / g (@ 20 A / g), but the retention rate was as high as 85%. It showed high retention characteristics. From this, when the product of Example 1 is used as an electrode in an electricity storage device in which the electrolyte is an ionic liquid, the product of Comparative Example 2 is high regardless of the low conductivity and high viscosity of the ionic liquid. It suggests that it may have rate characteristics.

As shown in Table 4, the products of Examples 3 to 5 also had a high specific capacity and high retention characteristics even at a high current density, like the products of Example 1.

From the above, it was confirmed that the product of the present invention is a material including a laminate in which RGO containing an ionic liquid is laminated, and is suitable as an electrode material for an electricity storage device using the ionic liquid as an electrolyte.

FIG. 14 is a graph showing a Ragone plot of the products of Example 1 and Comparative Example 2.

According to FIG. 14, the energy density of the product of Example 1 did not substantially decrease with the increase of the power density, compared with that of the product of Comparative Example 2. For example, the energy density of the product of Example 1 at a power density of 18 kW / kg was 49 Wh / kg, significantly higher than that of the product of Comparative Example 2 (29 Wh / kg). Although not shown, the products of Examples 3 to 5 showed the same tendency as the product of Example 1.

FIG. 15 is a diagram showing cycle characteristics of the products of Example 1 and Comparative Example 2.

The product of Example 1 had a high capacity retention of 92% even after 2000 repeated cycles at a current density of 10 A / g, which was higher than that of the product of Comparative Example 2 (82%). Although not shown, the products of Examples 3 to 5 showed the same results as the product of Example 1.

From the above, it was confirmed that the product of the present invention is suitable as an electrode material for an electricity storage device using an ionic liquid as an electrolyte.

FIG. 16 is a diagram showing a Nyquist plot of the products of Example 1 and Comparative Example 2.

According to FIG. 16, the equivalent series resistance (ESR; 4.7Ω) obtained from the x-axis intercept of the product of Example 1 is smaller than that of the product of Comparative Example 2 (6.1Ω). It was found that the product of Example 1 can make good contact with the current collector. This is because the product of Example 1 has a porous structure consisting of hierarchical curved sheets, as described with reference to FIGS. Based on being offered.

As shown in the inset of FIG. 16, the diameter of the semicircle represents the charge transport resistance (R _ct ) and is related to the transport of electrolyte ions at the interface between the electrode and the electrolyte. The R _ct of the product of Example 1 was 0.86Ω, which was only a quarter of the R _ct (3.5Ω) of the product of Comparative Example 2. When the resistance is reduced, the adsorption / desorption of ions is promoted, and the rate characteristics of the electric double layer capacitor are improved. Similarly, the R _ct of the products of Examples 3-5 was also low.

FIG. 17 is a diagram showing the frequency dependence of the normalized specific capacity of the products of Example 1 and Comparative Example 2.

The operating frequencies f _0.5 of the products of Example 1 and Comparative Example 2 (frequency at which the capacity is 50% of the maximum value) were 18.60 Hz and 5.75 Hz, respectively. The relaxation time constants τ ₀ (= 1 / f _0.5 ) of the products of Example 1 and Comparative Example 2 obtained from these values were 53.6 ms and 173.9 ms, respectively. Although not shown, it was confirmed that the frequency responses of the products of Examples 3 to 5 were also faster than those of the product of Comparative Example 2.

From the above, the product of the present invention is a material including a laminate in which RGO containing an ionic liquid is laminated, and it is confirmed that the consistency between the product of the present invention and the electrolyte that is the ionic liquid is improved. It was done.

If the electrode material of the present invention is used in an electricity storage device using an ionic liquid as an electrolyte, the rate characteristics of the electrode material are improved, and quick charge / discharge is possible while achieving high output density and high energy density. If such an electricity storage device is an electric double layer capacitor, it is advantageous for wind power generation, electric vehicles and the like. If such an electricity storage device is a lithium ion battery, it is advantageous for portable electronic devices such as notebook computers and mobile phones.

100 Electrode material 110 Graphene oxide (RGO)
120 laminate 130 ionic liquid 400 electric double layer capacitor 410 positive electrode 420 negative electrode transmission 430 electrolyte 440 separator 450 cell

Claims (19)

1. An electrode material including a laminate in which reduced graphene oxide is laminated,
   The laminate is an electrode material containing an ionic liquid between the reduced graphene oxides.
2. 2. The electrode material according to claim 1, wherein the weight ratio of the ionic liquid to the reduced graphene oxide is in the range of 0.01 to 1.00.
3. 3. The electrode material according to claim 2, wherein a weight ratio of the ionic liquid to the reduced graphene oxide is in a range of 0.02 to 0.60.
4. The electrode material according to claim 1, wherein a specific surface area of the laminate is in a range of 350 m ² / g to 500 m ² / g.
5. 5. The electrode material according to claim 4, wherein the specific surface area of the laminate is in a range of 420 m ² / g or more and 450 m ² / g or less.
6. The electrode material according to claim 1, wherein a pore volume of the laminate is in a range of 0.75 cc / g to 1.5 cc / g.
7. The electrode material according to claim 6, wherein a pore volume of the laminate is in a range of 0.85 cc / g or more and 0.95 cc / g or less.
8. The ionic liquids are 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF ₄ ), 1-ethyl-3-methylimidazolium-bis (fluorosulfonyl) imide (EMIFSI), 1-ethyl-3-methylimidazole Rium-bis (trifluoromethanesulfonyl) imide (EMITFSI), 1-butyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (BMITSI), 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIBF ₄ ) , 1-hexyl-3-methylimidazolium - bis (trifluoromethanesulfonyl) imide (HMITFSI), 1-ethyl-3-methylimidazolium - fluorohydrocarbon oxygenate _{(EMI (FH) 2.3 F)} , N, N Diethyl -N- methyl -N- (2-methoxyethyl) - tetrafluoroborate (DEMEBF _4), N, N- diethyl--N- methyl -N- (2-methoxyethyl) - bis (trifluoromethanesulfonyl) imide ( DEMETFSI), N-methyl-N-propylpiperidinium-bis (trifluoromethanesulfonyl) imide (PP13TFSI), triethylsulfonium-bis (trifluoromethanesulfonyl) imide (TESTFSI), N-methyl-Npropylpyrrolidinium-bis (Trifluoromethanesulfonyl) imide (P13TFSI), triethyloctylphosphonium-bis (trifluoromethanesulfonyl) imide (P2228TFSI), N-methyl-methoxymethylpyrrolidinium-tetrafluorovole The electrode according to claim 1, wherein the electrode is selected from the group consisting of lithium (C13BF ₄ ), lithium-bis (fluorosulfonyl) imide (LiFSI), and lithium-bis (trifluoromethanesulfonyl) imide (LiTFSI). material.
9. The electrode material according to claim 1, wherein the laminate has mesopores having a diameter in the range of 2 nm to 6 nm and macropores having a diameter of 50 nm or more.
10. The electrode material according to claim 1, wherein the laminate has a specific capacity in a range of 80 F / g or more and 140 F / g or less at a current density of 20 A / g.
11. A method for producing the electrode material according to any one of claims 1 to 10,
    Preparing a suspension of graphene oxide and ionic liquid added to a polar solvent;
    Adding a reducing agent to the suspension and refluxing.
12. The method according to claim 11, wherein in the preparing step, a weight ratio of the ionic liquid to the graphene oxide is 0.005 or more and 0.5 or less.
13. The method according to claim 12, wherein in the preparing step, a weight ratio of the ionic liquid to the graphene oxide is 0.01 or more and 0.3 or less.
14. 12. The method of claim 11, wherein the polar solvent is selected from the group consisting of water, dimethyl sulfoxide (DMSO), N, N-dimethylsulfamide (DMF) and ethanol.
15. The ionic liquid includes 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF ₄ ), 1-ethyl-3-methylimidazolium-bis (fluorosulfonyl) imide (EMIFSI), 1-ethyl-3-methylimidazole Rium-bis (trifluoromethanesulfonyl) imide (EMITFSI), 1-butyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (BMITSI), 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIBF ₄ ) 1-hexyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide (HMITFSI), 1-ethyl-3-methylimidazolium-fluorohydrogenate (EMI (FH) _2.3 F), N, N - Ethyl -N- methyl -N- (2-methoxyethyl) - tetrafluoroborate (DEMEBF _4), N, N- diethyl--N- methyl -N- (2-methoxyethyl) - bis (trifluoromethanesulfonyl) imide ( DEMETFSI), N-methyl-N-propylpiperidinium-bis (trifluoromethanesulfonyl) imide (PP13TFSI), triethylsulfonium-bis (trifluoromethanesulfonyl) imide (TESTFSI), N-methyl-Npropylpyrrolidinium-bis (Trifluoromethanesulfonyl) imide (P13TFSI), triethyloctylphosphonium-bis (trifluoromethanesulfonyl) imide (P2228TFSI), N-methyl-methoxymethylpyrrolidinium-tetrafluoroborate (C13BF _4), lithium - bis (fluorosulfonyl) imide (LiFSI), and lithium - bis is at least one selected from the group consisting of (trifluoromethanesulfonyl) imide (LiTFSI), The method of claim 11.
16. The reducing agent includes hydrazine, dimethylhydrazine, ascorbic acid, hydroquinone, sodium borohydride (NaBH ₄ ), tetrabutylammonium bromide (TBAB), LiAlH ₄ , ethylene glycol, polyethylene glycol, hydrogen iodide, and N, N 12. The method of claim 11, wherein at least one is selected from the group consisting of diethylhydroxylamine.
17. An electricity storage device comprising an electrode and an electrolyte,
    The electricity storage device, wherein the electrode is made of the electrode material according to any one of claims 1 to 10.
18. The electricity storage device is an electric double layer capacitor,
    The electrolyte is an ionic liquid;
    The electricity storage device according to claim 17, wherein the ionic liquid is the same as the ionic liquid contained in the electrode material.
19. The electricity storage device is a lithium ion battery,
    The electrolyte is an ionic liquid containing lithium,
    The electricity storage device according to claim 17, wherein the ionic liquid containing lithium is the same as the ionic liquid contained in the electrode material.

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