JP6313636B2 - Superlattice structure, manufacturing method thereof, and electrode material using the same - Google Patents

Description

  The present invention relates to a superlattice structure using a double hydroxide nanosheet, a manufacturing method thereof, and an electrode material using the same.

  As demand for limited fossil fuels increases, research into alternative energy conversion / storage systems such as fuel cells, solar cells, secondary lithium-ion batteries, and supercapacitors is actively underway. Among them, the supercapacitor is most advantageous from the viewpoint of high power density (about 5 kW / kg). However, the energy density of the supercapacitor is 10 Wh / kg or less (100 F / g or less in terms of specific capacity), which is known to be extremely small compared to that of the secondary lithium ion battery (about 200 Wh / g). In order to put the super capacitor into practical use, it is necessary to increase the capacitance by at least 2 to 5 times.

  There are two electrochemical processes for energy storage and release of supercapacitors: ion adsorption / desorption processes and oxidation / reduction reactions. By utilizing fast adsorption / desorption of ions to / from conductive surfaces, high power electric double layer (EDL) supercapacitors can be constructed. As the electrode active material of such a supercapacitor, a carbon material having a high specific surface area such as activated carbon, carbon nanotube, graphene, or the like is employed.

On the other hand, in a pseudo-capacitor capacitor, which is a high-capacity device using oxidation / reduction reactions as in the case of a battery, an oxide of a transition metal (Fe, Co, Ni, Mn, Ru, etc.) that can be oxidized / reduced as an electrode material / Hydroxide is used. However, except for RuO ₂ (Ru is a rare and expensive metal) exhibiting high conductivity, other transition metal oxides / hydroxides have high insulating properties and are difficult to use as electrode materials as they are. It is.

In order to solve such problems, a method has been proposed in which a conductive carbon material containing carbon nanotubes and graphene is combined with a transition metal oxide / hydroxide to improve electrochemical characteristics. In particular, since graphene has a high specific surface area (about 2600 m ² / g) and high conductivity (10 ³ to 10 ⁴ S / cm), it enables a large EDL capacity and efficiently collects current. Function as.

  A technique in which a carbon material and a transition metal hydroxide are combined has been reported (see, for example, Patent Document 1 and Non-Patent Document 1).

  According to Patent Document 1 and Non-Patent Document 1, for example, a suspension in which a double hydroxide nanosheet containing Co and Al (Co—Al layered double hydroxide nanosheet) is dispersed, and a graphene oxide nanosheet are dispersed. By mixing the suspension, a composite of graphene oxide nanosheets and Co-Al layered double hydroxide nanosheets can be obtained by electrostatic interaction, which is effective as an electrode material for supercapacitors Is disclosed.

  However, in the composites described in Patent Document 1 and Non-Patent Document 1, nanosheets may be aggregated, and a laminated structure in which insulating double hydroxide nanosheets and conductive graphene nanosheets are directly adjacent to each other is obtained. I can't. Further, it is necessary to improve the characteristics in order to apply to an actual super capacitor or pseudo capacitor.

Chinese Patent Application Publication No. 101955933

Lei Wang et al., Chem. Commun. , 2011, 47, 3556-3558

  As described above, an object of the present invention is to provide a superlattice structure suitable for a supercapacitor, a pseudocapacitor capacitor, a manufacturing method thereof, and an electrode material using the same.

In the superlattice structure of the present invention, double hydroxide nanosheets containing M1 ²⁺ ions and M2 ³⁺ ions and reduced graphene oxide nanosheets are alternately stacked, and the M1 element of the M1 ²⁺ ions is , Co, Fe, Ni, Mn, Cu and Zn, and the M2 element of the M2 ³⁺ ion is selected from Al, Cr, Mn, Fe, Co, Ni and Ga. It is a metal element selected from at least one group, and the interlayer distance is in the range of 0.8 nm or more and less than 1.3 nm, thereby solving the above problem.
The M1 element may be Co, and the M2 element may be Al.
The M1 element may be Co and Ni, and the M2 element may be Co.
The double hydroxide nanosheet may have a thickness in a range of 0.48 nm to 1.0 nm.
The reduced graphene oxide nanosheet may have a thickness in a range of 0.33 nm to 0.83 nm.
The interlayer distance may be in a range of 0.8 nm or more and less than 1.1 nm.
The double hydroxide nanosheet may be represented by a general formula [M1 ²⁺ _1−x M2 ³⁺ _x (OH) ₂ ] ^{x +} (x is a real number of 0 <x ≦ 1/3).
The double hydroxide nanosheet represented by the general formula _{^{[M1 2+ 1-x M2 3+}} x (OH) 2] [Z n- x / n · mH 2 O] (Z is an anion, n represents the anion Z And x is a real number satisfying 0 <x ≦ 1/3, and m is a real number satisfying 0 <m <1). .
The reduced graphene oxide nanosheet may be reduced after being peeled from the graphene oxide as a single layer.
Using the mass (G) of graphite as a precursor as the mass of the reduced graphene oxide nanosheet, the layer containing the M1 ²⁺ ion and the M2 ³⁺ ion as a precursor as the mass of the double hydroxide nanosheet When the double hydroxide mass (LDH) is used, the ratio (LDH / G) of the layered double hydroxide mass (LDH) to the graphite mass (G) is 3 or more and less than 4. Good.
The above-described method for manufacturing a superlattice structure according to the present invention is reduced by a cationic solution in which a double hydroxide nanosheet containing M1 ²⁺ ions and M2 ³⁺ ions is dispersed in a first aprotic polar solvent. The step of mixing and stirring the anionic solution in which the graphene oxide nanosheet is dispersed in at least the second aprotic polar solvent is included, thereby solving the above-mentioned problem.
In the mixing and stirring step, the M1 ²⁺ ion and the M2 ³⁺ ion that are the precursor of the double hydroxide nanosheet with respect to the mass (G) of the graphite that is the precursor of the reduced graphene oxide nanosheet are contained The ratio of the layered double hydroxide mass (LDH) (LDH / G) may be 3 or more and less than 4.
In the anionic solution, the reduced graphene oxide nanosheet may be dispersed in a mixed solvent of the second aprotic polar solvent and water.
In the mixed solvent, the volume ratio (H / F) of the water (H) to the second aprotic polar solvent (F) may be in the range of 0 to 0.5.
The first aprotic polar solvent may be selected from the group consisting of formamide, dimethyl sulfoxide, methylformamide, and dimethylformamide.
The second aprotic polar solvent may be selected from the group consisting of formamide, dimethyl sulfoxide, methylformamide, and dimethylformamide.
In the mixing and stirring step, the anionic solution may be added at a rate of 1 mL / min to 10 mL / min while stirring the cationic solution at room temperature.
In the mixing / stirring step, the cationic solution may be added at a rate of 1 mL / min to 10 mL / min while stirring the anionic solution at room temperature.
Prior to the step of mixing and stirring, the method further includes a step of preparing an anionic solution by adding a reducing agent to a solution in which graphene oxide nanosheets are dispersed in at least a second aprotic polar solvent and then heating the solution. Good.
The electrode material according to the present invention comprises the superlattice structure described above, thereby solving the above-mentioned problems.

  In the superlattice structure of the present invention, double hydroxide nanosheets and reduced graphene oxide nanosheets are alternately laminated, and the interlayer distance is in the range of 0.8 nm or more and less than 1.3 nm. The superlattice structure having such a structure is formed by alternately laminating nanosheets without aggregation, and may have excellent electrochemical characteristics. Since the double hydroxide nanosheet that can be oxidized / reduced is used, a high capacity is possible if the superlattice structure of the present invention is used as an electrode material. In addition, since the insulating double hydroxide nanosheets and the conductive reduced graphene oxide nanosheets are alternately arranged at the molecular level, the charge transport efficiency can be improved. As a result, when the superlattice structure of the present invention is used as an electrode material, high output performance of high-speed charging / discharging comparable to reduced graphene oxide nanosheets is enabled.

  According to the method of the present invention, since an anionic solution in which reduced graphene oxide nanosheets are dispersed in at least an aprotic polar solvent is used, impurities are reduced and a high-quality superlattice structure is obtained.

Schematic diagram of the superlattice structure of the present invention The figure which shows the step which manufactures the superlattice structure of this invention The figure which shows the AFM image of the sample of the reference example 1 The figure which shows the AFM image (A), TEM image (B), and electron diffraction pattern (C) of the sample of the reference example 2. The figure which shows the AFM image of the sample of the reference example 3 and the reference example 4 The figure which shows the XRD pattern of the sample of the reference example 3 and the reference example 4 The figure which shows the TEM image of the sample of the reference example 3 and the reference example 4 The figure which shows the electron diffraction pattern (A) and EELS spectrum (B) of the sample of Reference Example 4 The figure which shows the XRD pattern of the sample of Example 5 and Comparative Example 6 The figure which shows the XRD pattern of the sample of Example 7 and Comparative Example 8 The figure which shows the TEM image (A), high-resolution image (B), and electron diffraction pattern (C) of the sample of Example 5. The figure which shows the TEM image (A), high-resolution image (B), and electron diffraction pattern (C) of the sample of Example 7. The figure which shows the elemental mapping of the sample of Example 5 The figure which shows the XRD pattern of the sample of the comparative example 9 The figure which shows the SEM image (A) and electrochemical property (B)-(D) of the sample of the reference example 1. The figure which shows the SEM image (A) and electrochemical property (B)-(D) of the sample of the reference example 2. The figure which shows the electrochemical characteristics (A)-(C) of the sample of the reference example 4 The figure which shows the electrochemical characteristics (A)-(C) of the sample of the comparative example 10 The figure which shows the electrochemical characteristics (A)-(C) of the sample of Example 5 The figure which shows the electrochemical characteristics (A)-(C) of the sample of Example 7 The figure which shows the result of the constant current charging / discharging (CD) measurement by the sample of the reference example 4, Example 5, and Example 7. The figure which shows the scanning speed dependence of the specific capacity of the sample of Reference Example 4, Example 5, Example 7, and Comparative Example 10 The figure which shows the behavior of the capacity | capacitance of the sample of Example 7.

  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.

  The structure of the superlattice structure of the present invention will be described.

  FIG. 1 shows a schematic diagram of a superlattice structure according to the present invention.

In the superlattice structure 100 of the present invention, double hydroxide nanosheets (LDH nanosheets) 110 containing M1 ²⁺ ions and M2 ³⁺ ions and reduced graphene oxide nanosheets (rGO nanosheets) 120 are alternately stacked. Structure. Here, the M1 element of the M1 ²⁺ ion is a metal element selected from the group consisting of Co, Fe, Ni, Mn, Cu and Zn, and the M2 element of the M2 ³⁺ ion is Al, Cr, Mn , Fe, Co, Ni, and Ga. At least one metal element selected from the group consisting of Ga. In the superlattice structure 100 of the present invention, the interlayer distance D is in the range of not less than 0.8 nm and less than 1.3 nm.

  For example, according to the composite described in Non-Patent Document 1 (or corresponding Patent Document 1), the interlayer distance is reported to be about 2.9 nm, and the value (0 A range of 8 nm or more and less than 1.3 nm). That is, the composite described in Non-Patent Document 1 (or corresponding Patent Document 1) is not a superlattice structure in which double hydroxide nanosheets and graphene nanosheets are alternately stacked, and is different from the present application.

  Since the superlattice structure 100 of the present invention uses the oxidizable / reducible LDH nanosheet 110, the use of the superlattice structure 100 of the present invention as an electrode material enables high capacity. Since the rGO nanosheet 120 is used instead of the graphene oxide nanosheet, the conductivity is high. Since such insulating LDH nanosheets 110 and conductive rGO nanosheets 120 are alternately arranged at the molecular level, the charge transport efficiency can be improved. As a result, when the superlattice structure 100 of the present invention is used as an electrode material, high output performance of high-speed charging / discharging comparable to reduced graphene oxide is enabled.

The LDH nanosheet 110 is represented by a general formula [M1 ²⁺ _1−x M2 ³⁺ _x (OH) ₂ ] ^{x +} (x is a real number where 0 <x ≦ 1/3). The M1 element and M2 element in the formula are as described above. Among these, a combination in which the M1 element is Co and the M2 element is Al, and a combination in which the M1 element is Co and Ni and the M2 element is Co are preferable because they are easy to manufacture. Further, a combination in which the M1 element is Co and Ni and the M2 element is Co is a transition metal, and is preferable because the characteristics are improved.

The LDH nanosheet 110 has the general formula [M1 ²⁺ _1-x M2 ³⁺ _x (OH) ₂ ] [Z ⁿ⁻ _{x / n} · mH ₂ O] (Z is an anion, and n is the valence of the anion Z). And x is a real number of 0 <x ≦ 1/3, and m is a real number of 0 <m <1). Z is arbitrary as long as it becomes an anion, but from the viewpoint of ease of production, nitrate ion, perchlorate ion, and halogen ion are preferable.

  The thickness d1 of the LDH nanosheet 110 has a crystallographic thickness calculated from the layered double hydroxide. Specifically, if the thickness d1 is in the range of 0.48 nm to 1.0 nm, It can be regarded as having a crystallographic thickness.

  The rGO nanosheet 120 is reduced after being separated from the graphene oxide by a single layer. The thickness d2 of the rGO nanosheet 120 is thinner than the thickness of the graphene oxide nanosheet, and specifically ranges from 0.33 nm to 0.83 nm. If the rGO nanosheet 120 satisfies this thickness, it can be said that it has been peeled off from the graphene oxide and is more reliably reduced.

  The interlayer distance D of the superlattice structure 100 of the present invention can be converted from the thickness d1 of the LDH nanosheet 110 and the thickness d2 of the rGO nanosheet 120 described above, but as described above, 0.8 nm or more and 1.3 nm. If it is less than the range, it is recognized that the LDH nanosheets 110 and the rGO nanosheets 120 are alternately laminated. More preferably, the interlayer distance D is in the range of 0.8 nm or more and less than 1.1 nm. If it is this range, it can be said that it is the superlattice structure 100 of very good quality.

  Further, the mass of graphite as a precursor (G) is used as the mass of the rGO nanosheet, the mass of the layered double hydroxide as a precursor (LDH) as the double hydroxide nanosheet, and the layered double water relative to the mass of graphite. When the ratio of the mass of the oxide (LDH / G) is calculated, it is preferably 3 or more and less than 4.

  By controlling the LDH / G value to satisfy 3 or more and less than 4, the inventors of the present application can form a high-quality superlattice structure in which the LDH nanosheets 110 and the rGO nanosheets 120 are laminated alternately and uniformly without agglomeration. I found out that I can take it by ingenuity. When the LDH / G value exceeds 4, the LDH nanosheet tends to aggregate, and when the LDH / G value is less than 3, the rGO nanosheet tends to aggregate.

  The superlattice structure 100 of the present invention has a specific capacity of at least 500 F / g or more at a scan speed of 10 mV / s, for example, due to the above-described laminated structure. Depending on the choice of the M1 and M2 elements of the LDH nanosheet in the superlattice structure, it is possible to increase the specific capacity up to 700 F / g. The specific capacity of the superlattice structure 100 of the present invention is six times that of graphene nanosheets, and can be an electrode material superior to graphene.

  The superlattice structure 100 of the present invention has high charge transport efficiency because the conductive rGO nanosheet is directly adjacent to the insulating LDH nanosheet. Moreover, the superlattice structure 100 of the present invention can maintain ideal capacitor characteristics up to about 100 Hz. Since this rate characteristic is comparable to an EDL supercapacitor using a graphene electrode, it is suitable as an electrode material for a pseudocapacitor capacitor or a supercapacitor.

  Next, a method for manufacturing the superlattice structure 100 of the present invention will be described.

  FIG. 2 is a diagram showing steps for manufacturing the superlattice structure of the present invention.

Step S210: a cationic solution in which a double hydroxide nanosheet (LDH nanosheet) containing M1 ²⁺ ions and M2 ³⁺ ions is dispersed in a first aprotic polar solvent, and a reduced graphene oxide nanosheet (rGO nanosheet) Is mixed and stirred with at least the anionic solution dispersed in the second aprotic polar solvent.

The LDH nanosheet is as described above with reference to FIG. The LDH nanosheet can be obtained by, for example, the hydrothermal synthesis method described in “Chem. Lett. 2004, 33, 1122” by Iyi et al. A layered double hydroxide (LDH) produced by the homogeneous precipitation method described in “J. Am. Chem. Soc. 2006, 128, 4872” by Liu et al. (General formula [M1 ²⁺ _1-x M2 ³⁺ _x (OH _{^{) 2] [Z n- x /}} n · mH 2 O] (Z is an anion, n is the valence of the anion Z, x is a real number of 0 <x ≦ 1/3, m is 1 is a real number such that 0 <m <1), or a method described in JP 2007-31189 or a method described in J. Liang et al., Chem. Mater. 2010, 22, 371 May be prepared.

  The prepared LDH nanosheet is dispersed in the first aprotic polar solvent as a dispersion medium to become a cationic solution. Here, the first aprotic polar solvent is selected from the group consisting of formamide, dimethyl sulfoxide, methylformamide, and dimethylformamide. These aprotic polar solvents are known to promote LDH exfoliation, and the exfoliated LDH nanosheets can be well maintained in a dispersed state without reaggregation.

  The rGO nanosheet is as described above with reference to FIG. The rGO nanosheet is obtained by reducing graphene oxide nanosheets (GO nanosheets) that have been exfoliated from graphite oxide. For example, graphite oxide is S.I. It can be obtained from natural graphite pieces (flaky graphite) by the modified Hamer method described by Park et al., “Nature Nanotechnol. 2009, 4, 217”. The graphite oxide is dispersed in water to form a slurry, and this is subjected to ultrasonic treatment to be separated into a single layer to form a GO nanosheet. The GO nanosheet is reduced by heating together with a reducing agent to become an rGO nanosheet.

  The prepared rGO nanosheet is dispersed in at least a second aprotic polar solvent as a dispersion medium to form an anionic solution. Here, the second aprotic polar solvent is selected from the group consisting of formamide, dimethyl sulfoxide, methylformamide, and dimethylformamide. The second aprotic polar solvent may be the same as the first aprotic polar solvent, or these solvents may be different because they solvate with each other. The second aprotic polar solvent can satisfactorily maintain the dispersed state of the peeled rGO nanosheet without reaggregation.

  Note that the rGO nanosheet may be dispersed in a mixed solvent of the second aprotic polar solvent and water as a dispersion medium to form an anionic solution. This is because when a graphite oxide is exfoliated, water is usually used as a dispersion medium. If an anionic solution contains a second aprotic polar solvent, a GO nanosheet or an rGO nanosheet is prepared. This is because the superlattice structure of the present invention is not inferior in production even if it contains residual water. Specifically, as a dispersion medium for the anionic solution, the volume ratio (H / F) of water (H) to the second aprotic polar solvent (F) should satisfy the range of 0 to 0.5. For example, when mixed with LDH nanosheets, the influence of carbonate ion impurities generated by carbon dioxide in the air can be ignored.

  Prior to the mixing / stirring step in step S210, an anionic solution containing rGO nanosheets is prepared by adding a reducing agent to a solution in which GO nanosheets are dispersed in at least a second aprotic polar solvent and then heating. It is preferable to do. By using the second aprotic polar solvent as a dispersion medium, impurities can be reduced and a high-quality rGO nanosheet can be obtained. The reducing agent is not particularly limited, and specific examples include hydrazine, urea, vitamin C, benzyl alcohol, hydrogen iodide (HI), and derivatives thereof. The heating may be typically held for 5 hours to 24 hours in a temperature range of 70 ° C. or higher and 100 ° C. or lower. Further, it is preferable to use an oil bath when heating, since the temperature can be kept constant, and the reduction proceeds uniformly.

  The ratio of the mass (LDH) of the layered double hydroxide that is the precursor of the LDH nanosheet to the mass (G) of the graphite that is the precursor of the rGO nanosheet is the cationic solution and the anionic solution thus prepared. (LDH / G) is mixed and stirred so that it is 3 or more and less than 4. Thereby, the superlattice structure laminated | stacked alternately can be comprised, without a LDH nanosheet and a rGO nanosheet aggregating.

  The cationic solution and the anionic solution thus prepared are mixed at a rate of 1 mL / min to 10 mL / min while stirring the cationic solution at room temperature (15 ° C. to 30 ° C.). Or the cationic solution is added at a rate of 1 mL / min to 10 mL / min while stirring the anionic solution at room temperature (15 ° C. to 30 ° C.). Thus, by slowly dropping a solution having an opposite charge at a predetermined speed, the LDH nanosheet and the rGO nanosheet are easily brought into contact with each other, and the alternate lamination can be promoted.

  The cationic solution and the anionic solution thus prepared are mixed and stirred, but the stirring conditions are not particularly limited. Illustratively, the agitation is performed for 10 minutes to 30 minutes in the range of rotation speeds of 100 rpm to 500 rpm.

  By step S210, the superlattice structure of the present invention is obtained as a precipitate. The obtained precipitate may be recovered by repeating ethanol washing and centrifugation.

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

[Reference Example 1]
Prior to the examples, LDH containing Co as the M1 element and Al as the M2 element, a film in which the LDH was densely packed, and an LDH nanosheet from which the LDH was peeled off were manufactured.

For example, Z. CoCl ₂ .6H ₂ O and AlCl ₃ containing urea (CO (NH ₂ ) ₂ ) as a hydrolysis reagent by the homogeneous precipitation method described in “J. Am. Chem. Soc. 2006, 128, 4872” by Liu et al. · 9H ₂ from O mixed solution of the ^{_{[Co 2+ 2/3 Al 3+ 1/3 (}} OH) 2] Co-Al carbonate type LDH expressed by _{[CO 3 2- 1/6 · 0.5H 2} O] Manufactured. The Co-Al carbonate type LDH was a uniform micrometer-sized hexagonal plate-like crystal (sometimes simply referred to as a Co-Al LDH plate). Subsequently, ion exchange was performed on the Co—Al carbonate type LDH using HCl and NaCl to obtain a Co—Al halogen type LDH. Note that Co—Al nitrate type LDH may be obtained using HNO ₃ and NaNO ₃ instead of HCl and NaCl.

Co-Al halogen type (or nitric acid type) LDH is dispersed in formamide (HCONO ₂ ) and then mechanically shaken to contain [Co ²⁺ _2/3 Al ³⁺ _1/3 (OH) ₂ ] ^{1 /} containing Co and Al. ^Single layer peeling was performed on an LDH nanosheet represented by ³⁺ (hereinafter referred to as a Co—Al LDH nanosheet). The zeta potential of the suspension in which Co-Al LDH nanosheets were dispersed in formamide was measured using an ELS-Z zeta potential and a particle size analyzer. The results will be described later.

The surface of the Co—Al LDH nanosheet was observed using an atomic force microscope (AFM, manufactured by Seiko, SPA400). Specifically, a Co—Al LDH nanosheet was deposited on a Si substrate and observed in a tapping mode using a Si cantilever (spring constant: about 20 Nm ⁻¹ ). The results are shown in FIG.

Subsequently, for example, R.K. Using the oil-water interface self-assembly procedure described in “Chem. Mater. 2010, 22, 6341” by Ma et al., The resulting plate-like crystals, Co-AL carbonate type LDH (Co-Al LDH plate) are densely packed. Plate plates were produced. Co-Al LDH plates (80 mg) were dispersed in 80 mL of MilliQ water. Next, hexane (8 mL) was added to this to form a hexane / water interface. Butanol (1.5 mL) was slowly injected, and a Co—Al LDH plate was trapped at the interface to form a continuous film. Hexane was evaporated, and the film floating at the interface was transferred to ITO glass (indium tin oxide, sheet resistance: about 10Ω / □, size: 1 × 3 cm ³ ) by the vertical pulling method. The Co-AL LDH plate film on ITO glass was dried at 80 ° C. for 24 hours.

  The surface of the Co—Al LDH plate film on the ITO glass was observed using a scanning electron microscope (SEM, manufactured by Keyence, VE8800). The results are shown in FIG.

  Co-Al LDH plate film on ITO glass as working electrode, KOH (1M) as electrolyte, Ag / AgCl as reference electrode, and platinum wire as counter electrode, at an electrochemical workstation (Solartron) Cyclic voltammetry (CV) measurement and electrochemical impedance spectroscopy measurement were performed. In electrochemical impedance spectroscopy, a potential amplitude of 10 mV was applied over a frequency range of 0.1 Hz to 10000 Hz. The results are shown in FIGS. 15 (B) to (D).

[Reference Example 2]
In Reference Example 2, LDH containing Co and Ni as the M1 element and Co as the M2 element, a dense film of the LDH, and an LDH nanosheet from which a single layer of LDH was peeled were manufactured.

For example, J. et al. LDH plate-like crystals containing Co and Ni were obtained by the topochemical oxidative intercalation method described in “Chem. Mater. 2010, 22, 371” by Liang et al. Hexamethylenetetramine as a hydrolysis reagent _{(HMT, C 6 H 12 N} 4) CoCl 2 · 6H 2 O and NiCl ₂ · 6H ₂ from O mixed solution of ^Co ₂₊ 2/3 ^Ni ₂₊ 1/3 containing _{(OH) 2} The blue site represented by Brusite was a uniform micrometer-sized hexagonal plate-like crystal. Subsequently, Co ²⁺ _2/3 Ni ²⁺ _1/3 (OH) ₂ is caused to partially oxidize Co ²⁺ by acting a bromine acetonitrile solution, while reducing bromine itself to intercalate bromine ions between the host layers. [Co ²⁺ _1/3 Ni ²⁺ _1/3 Co ^{3 +} _1/3 (OH) ₂ ] [Br ⁻ _1/3 · 0.5H ₂ O] (Co—Ni halogen type LDH or Co—Ni LDH plate) Obtained).

Co-Ni halogen type LDH is anion-exchanged with NO ₃ ⁻ (or ClO ₄ ⁻ ), dispersed in formamide (HCONH ₂ ), mechanically shaken, and contains Co and Ni. [Co ²⁺ _1/3 Ni ²⁺ _{1 / 3} Co ³⁺ _1/3 (OH) ₂ ] A single layer was peeled to an LDH nanosheet represented by _1/3 ⁺ (hereinafter referred to as a Co—Ni LDH nanosheet). The potential of the suspension in which Co-Ni LDH nanosheets were dispersed in formamide was measured using an ELS-Z zeta potential and a particle size analyzer. The results will be described later.

  Similar to Reference Example 1, the surface of the Co—Ni LDH nanosheet was observed using AFM. The results are shown in FIG. Transmission electron microscope (TEM, JEOL, JEM-3100F energy filtering (omega type) equipped with an energy dispersive X-ray analyzer (EDS) and an electron energy loss spectrometer (EELS) on the surface of the Co-Ni LDH nanosheet Observation with a microscope) gave an electron diffraction pattern. The results are shown in FIGS.

  As in Reference Example 1, a plate film in which the obtained Co—Ni LDH plates were densely formed was formed on ITO glass. Similar to Reference Example 1, the surface of the Co—Ni LDH plate film on ITO glass was observed with SEM. The results are shown in FIG.

  Electrochemical workstation using Co-Ni LDH plate film on ITO glass as working electrode, KOH (1M) as electrolyte, Ag / AgCl as reference electrode, and platinum wire as counter electrode, as in Reference Example 1. Cyclic voltammetry (CV) measurement and electrochemical impedance spectroscopic measurement were carried out (manufactured by Solartron). The results are shown in FIGS.

[Reference Example 3]
In Reference Example 3, a graphite oxide and a graphene oxide nanosheet (GO nanosheet) from which a single layer was peeled were manufactured.

For example, S.M. Graphite oxide was produced from natural graphite pieces (purity 99.9999%, 100 mesh) by the modified Hammer method described by Park et al., “Nature Nanotechnol. 2009, 4, 217”. Natural graphite (1 g) was stirred in a mixed solution of KNO ₃ (1.2 g) and H ₂ SO ₄ (50 mL) in a 1000 mL conical beaker. Next, KMnO ₄ (6 g) was slowly added, and the mixture was stirred at room temperature (15 ° C. or higher and 30 ° C. or lower) for 6 hours. The conical beaker was placed in a cooling bath, and Milli-Q water (30 mL) was slowly added while maintaining the temperature at 80 ° C. or lower. Further MilliQ water (200 mL) was added to dilute the suspension. To this suspension was slowly added H ₂ O ₂ (6 mL) followed by MilliQ water and diluted to 1000 mL. The suspension settled and the supernatant was removed. Sedimentation and removal of the supernatant were repeated several times until the pH reached 5 or higher. As a result, graphite oxide was obtained from natural graphite. In addition, about the natural graphite piece, the X-ray-diffraction (XRD) measurement was performed with the X-ray-diffraction apparatus (Rigaku, Rint-2200) using the monochromatic CuK (alpha) ray ((lambda) = 1.5405cm). A result is shown to A in FIG.

  The graphite oxide slurry was dispersed in water and subjected to ultrasonic treatment to separate a single layer to obtain a graphite oxide nanosheet (GO nanosheet). After sonication for about 2 hours, a brown colloidal suspension was obtained.

  Similar to Reference Example 2, the surface of the GO nanosheet was observed using AFM and TEM. The results are shown in FIGS. 5 (A) and 7 (A). XRD measurement was performed on the GO nanosheet. A result is shown to B in FIG. The zeta potential of the suspension in which the GO nanosheet was dispersed in water was measured. The results will be described later.

[Reference Example 4]
In Reference Example 4, a graphene oxide nanosheet (rGO nanosheet) obtained by reducing the graphene oxide nanosheet (GO nanosheet) manufactured in Reference Example 3 and a film in which the graphene oxide nanosheet was densely manufactured were manufactured.

A suspension (1 mg / mL, 10 mL) of the GO nanosheet obtained in Reference Example 3 dispersed in water was mixed with formamide (90 mL). Hydrazine monohydrate (N ₂ H ₄ .H ₂ O, 8 μL) was added to this mixed solution, heated to 80 ° C. in an oil bath, and held for 12 hours. Here, the volume ratio (H / F) of water (H) to formamide (F) in the suspension was 1/9. After heating, a black suspension was obtained indicating that the GO nanosheet was reduced to the rGO nanosheet.

  Similar to Reference Example 2, the surface of the rGO nanosheet was observed using AFM. The results are shown in FIG. About rGO nanosheet, it observed using TEM and measured the electron diffraction pattern and the EELS spectrum pattern. The results are shown in FIG. 7 (B) and FIG. XRD measurement was performed on the rGO nanosheet. The results are shown in C in FIG. The zeta potential of the suspension in which the rGO nanosheet was dispersed in a mixed solvent of formamide and water (water: formamide = 1: 9 (volume)) was measured. The results will be described later.

  An rGO nanosheet suspension was dropped onto ITO glass, and a film composed of rGO nanosheets (simply referred to as an rGO nanosheet film) was formed by spin coating. As in Reference Example 1, CGO measurement and electrochemical impedance spectroscopy measurement were performed using an rGO nanosheet film on ITO glass as a working electrode. Moreover, the constant current charge / discharge (CD) measurement was performed using the rGO nanosheet film. These results are shown in FIG. 17 and FIG.

  From the result of CD measurement, the formula C = IΔt / mΔV (I is the charging current or discharging current, Δt is the time until full charging or discharging, m is the mass of the active material, and ΔV is the potential change after full charging or discharging. Was used to calculate the specific capacity. The results are shown in FIG.

[Example 5]
In Example 5, a superlattice structure of the Co—Al LDH nanosheet manufactured in Reference Example 1 and the rGO nanosheet manufactured in Reference Example 4 was manufactured. In Example 5, the ratio (LDH / G) of the mass (LDH) of Co—Al LDH as the Co—Al LDH nanosheet to the mass (G) of graphite as the rGO nanosheet was 3.04.

  A cationic solution was prepared by dispersing the Co—Al LDH nanosheet produced in Reference Example 1 in formamide as the first aprotic polar solvent. An anionic solution was prepared by dispersing the rGO nanosheet produced in Reference Example 5 in a mixed solvent of formamide and water as a second aprotic polar solvent. Here, the volume ratio (H / F) of water (H) to formamide (F) was 1/9.

  The cationic solution and the anionic solution were mixed and stirred (step S210 in FIG. 2). Specifically, the anionic solution was added at a rate in the range of 1 mL / min to 10 mL / min while stirring the cationic solution at room temperature (15 ° C. to 30 ° C.). The cationic Co-Al LDH nanosheet in the cationic solution and the anionic rGO nanosheet in the anionic solution formed a structure by electrostatic interaction and were deposited. The precipitate was centrifuged (rotation speed: 6000 rpm) and washed with ethanol. This process was repeated several times.

  The obtained structure was subjected to XRD measurement and TEM observation as in Reference Example 3. The results are shown in FIG. 9 and FIG. Element mapping was performed on the structure by EDS. The results are shown in FIG.

  The structure (1 mg) was dispersed in MilliQ water (500 μL) and mixed with Nafion® solution (10 μL). 50 μL of this was dropped onto ITO glass and spin-coated to obtain a film made of a structure. The film on ITO glass was dried at 80 ° C. for 24 hours and used as a working electrode for electrochemical measurement.

  As in Reference Example 4, CV measurement, CD measurement, and electrochemical impedance spectroscopy measurement were performed using a film made of a structure on ITO glass as a working electrode. The results are shown in FIG. 19, FIG. 21 (B) and FIG.

[Comparative Example 6]
In Comparative Example 6, a superlattice structure of the Co—Al LDH nanosheet manufactured in Reference Example 1 and the GO nanosheet manufactured in Reference Example 3 was manufactured. In Comparative Example 6, the ratio (LDH / G) of the mass (LDH) of Co—Al LDH that is a precursor of the Co—Al LDH nanosheet to the mass (G) of graphite as the GO nanosheet was 3.04. The production procedure was the same as in Example 5. The obtained structure was subjected to XRD measurement in the same manner as in Reference Example 3. The results are shown in FIG. Similarly to Reference Example 4, CV measurement, CD measurement, and electrochemical impedance spectroscopy measurement were performed using a film made of a structure on ITO glass as a working electrode.

[Example 7]
In Example 7, a superlattice structure of the Co—Ni LDH nanosheet manufactured in Reference Example 2 and the rGO nanosheet manufactured in Reference Example 4 was manufactured. In Example 7, the ratio (LDH / G) of the mass (LDH) of Co—Ni LDH, which is a precursor of the Co—Ni LDH nanosheet, to the mass (G) of graphite as the rGO nanosheet was 3.33. The production procedure was the same as in Example 5.

  The obtained structure was subjected to XRD measurement and TEM observation as in Reference Example 3. The results are shown in FIG. 10 and FIG.

  As in Reference Example 1, CV measurement, CD measurement, and electrochemical impedance spectroscopy measurement were performed using a film made of a structure on ITO glass as a working electrode. The results are shown in FIG. 20, FIG. 21 (C), FIG. 22 and FIG.

[Comparative Example 8]
In Comparative Example 8, a superlattice structure of the Co—Ni LDH nanosheet manufactured in Reference Example 2 and the GO nanosheet manufactured in Reference Example 3 was manufactured. In Comparative Example 8, the ratio (LDH / G) of the mass (LDH) of Co—Ni LDH, which is a precursor of the Co—Ni LDH nanosheet, to the mass (G) of graphite as the GO nanosheet was 3.33. The production procedure was the same as in Example 5. The obtained structure was subjected to XRD measurement in the same manner as in Reference Example 3. The results are shown in FIG. Similarly to Reference Example 4, CV measurement, CD measurement, and electrochemical impedance spectroscopy measurement were performed using a film made of a structure on ITO glass as a working electrode.

[Comparative Example 9]
In Comparative Example 9, a superlattice structure of the Co—Al LDH nanosheet manufactured in Reference Example 1 and the GO nanosheet manufactured in Reference Example 3 was manufactured. In Comparative Example 9, the ratio (LDH / G) of the mass (LDH) of Co—Al LDH, which is a precursor of the Co—Al LDH nanosheet, to the mass (G) of graphite as the GO nanosheet is 4.0 and 5.0. There were two types. The production procedure was the same as in Example 5. The obtained structure was subjected to XRD measurement in the same manner as in Reference Example 3. The results are shown in FIG.

[Comparative Example 10]
In Comparative Example 10, a mixture of the re-agglomerated Co—Al LDH nanosheet produced in Reference Example 1 and the re-agglomerated rGO nanosheet produced in Reference Example 4 was produced. In Comparative Example 10, the ratio (LDH / G) of the mass (LDH) of the layered double hydroxide in the re-agglomerated Co—Al LDH nanosheet to the mass (G) of the graphite in the re-agglomerated rGO nanosheet. 3.0.

  Co-Al LDH nanosheets were dispersed in formamide, and a KCl formamide solution (1M) was added thereto to obtain a re-aggregate of Co-Al LDH nanosheets. Similarly, rGO nanosheets were dispersed in formamide, and a KCl aqueous solution (1 M) was added thereto to obtain re-aggregates of rGO nanosheets. Co-Al LDH nanosheet reagglomerates and rGO nanosheet reagglomerates were mixed to obtain a mixture.

  As in Reference Example 3, CV measurement, CD measurement, and electrochemical impedance spectroscopy measurement were performed using a film made of a mixture on ITO glass as a working electrode. The results are shown in FIG. 18 and FIG.

  The above Reference Examples, Examples and Comparative Examples are summarized in Table 1 for simplicity.

  FIG. 3 is a diagram showing an AFM image of the sample of Reference Example 1.

  The sample for measurement is a Co—Al LDH nanosheet deposited on a Si substrate. According to FIG. 3, the thickness of the Co—Al LDH nanosheet was about 0.8 nm. This thickness was consistent with the value reported for monolayer exfoliated LDH nanosheet monolayers and was close to the crystallographic thickness. Moreover, the size in the horizontal direction (longitudinal direction) of the Co—Al LDH nanosheet was several micrometers (0.5 μm to 5 μm).

  4 is a diagram showing an AFM image (A), a TEM image (B), and an electron diffraction pattern (C) of the sample of Reference Example 2. FIG.

  A sample for AFM is a Co—Ni LDH nanosheet deposited on a Si substrate. The sample for TEM is a Co—Ni LDH nanosheet deposited on a microgrid. According to FIG. 4A, the thickness of the Co—Ni LDH nanosheet was about 0.8 nm, as in FIG. The lateral size of the Co—Ni LDH nanosheet was smaller than that of the Co—Al LDH nanosheet, and was several hundred nanometers (100 nm to 2000 nm).

  According to FIG. 4 (B), the region where the contrast is dark and shown uniformly indicates the Co—Ni LDH nanosheet, which reflects the fact that the single layer is peeled and the thickness is extremely thin.

  According to FIG. 4C, the in-plane diffraction spots are arranged in a hexagonal symmetry having a lattice constant a = 0.31 nm, and it was confirmed that each of the Co—Ni LDH nanosheets is single crystal. .

  As described above, according to FIG. 3 and FIG. 4, it was found that a single-layer LDH nanosheet was obtained by peeling a single layer from a layered double hydroxide and having a molecular level thickness of 0.8 nm. .

  FIG. 5 is a diagram showing AFM images of samples according to Reference Example 3 and Reference Example 4.

  Samples for AFM are GO nanosheets and rGO nanosheets deposited on a Si substrate. FIGS. 5A and 5B show the results of the GO nanosheet and the rGO nanosheet, respectively. According to FIG. 5 (A), the thickness of the GO nanosheet was about 1.0 nm. Moreover, the magnitude | size of the horizontal direction (longitudinal direction) of GO nanosheet was several micrometers (1 micrometer-10 micrometers).

  On the other hand, according to FIG. 5 (B), the thickness of the rGO nanosheet was thinner than that of the GO nanosheet, and was about 0.5 nm. This suggests that the functional group containing oxygen (for example, a hydroxyl group, a carboxyl group, an epoxy group, etc.) was removed from the GO nanosheet and reduced. Further, comparing FIGS. 5A and 5B, it was found that the rGO nanosheet is less curved and flatter than the GO nanosheet.

  FIG. 6 is a diagram showing XRD patterns of samples according to Reference Example 3 and Reference Example 4.

  XRD patterns A to C show the results of natural graphite pieces, GO nanosheets and rGO nanosheets, respectively. The interlayer distance calculated from the XRD patterns of the GO nanosheet and the rGO nanosheet was 0.83 nm and 0.4 nm, respectively.

  The interlayer distance (0.83 nm) of the GO nanosheet is smaller than the film thickness (1.0 nm) of the GO nanosheet obtained in FIG. 5A, and the interlayer distance (0.4 nm) of the rGO nanosheet is Since the film thickness is smaller than that of the rGO nanosheet obtained in FIG. 5B (0.5 nm), it is suggested that adsorbates such as moisture are present on the surfaces of the GO nanosheet and the rGO nanosheet during AFM observation.

  FIG. 7 is a diagram showing TEM images of samples according to Reference Example 3 and Reference Example 4.

  Samples for TEM are GO nanosheets and rGO nanosheets deposited on a microgrid. FIGS. 7A and 7B show the results of the GO nanosheet and the rGO nanosheet, respectively. According to FIG. 7, the regions that are slightly dark and shown uniformly (regions indicated by arrows in the figure) indicate GO nanosheets and rGO nanosheets, both of which are exfoliated and have a very thin thickness. It was confirmed.

  8 is a diagram showing an electron diffraction pattern (A) and an EELS spectrum (B) of a sample according to Reference Example 4. FIG.

  Again, the sample is an rGO nanosheet deposited on a microgrid. According to FIG. 8A, the in-plane diffraction spots are arranged in a hexagonal symmetry having a lattice constant a = 0.25 nm, and it was confirmed that each rGO nanosheet is single crystal.

According to FIG. 8B, a clear 1s → π ^* carbon peak (@ 284 eV) appears, but an oxygen peak (@ 532 eV) does not appear. This indicates that the aromatic sp ² carbon bond was partially restored in the rGO nanosheet.

  Next, the measured zeta potential will be described. The zeta potentials of Co-Al LDH nanosheet / Co-Ni LDH nanosheet, GO nanosheet and rGO nanosheet are + (50 ± 4) mV, − (45 ± 5) mV and − (36.5 ± 8) mV, respectively. there were. The zeta potential of the rGO nanosheet decreased from the zeta potential of the GO nanosheet depending on the degree of reduction of the GO nanosheet.

  From these results, it was found that all of the nanosheets were well dispersed in the dispersion medium and stably maintained in a colloidal state for a long time. In addition, the Co-Al LDH nanosheet / Co-Ni LDH nanosheet and the rGO nanosheet have opposite charges of relatively close values, suggesting that they can be alternately stacked by electrostatic interaction. To do.

FIG. 9 is a diagram showing XRD patterns of samples of Example 5 and Comparative Example 6.
FIG. 10 is a diagram showing XRD patterns of samples of Example 7 and Comparative Example 8.

  Samples of Example 5, Comparative Example 6, Example 7 and Comparative Example 8 were respectively a structure of Co—Al LDH nanosheet and rGO nanosheet, a structure of Co—Al LDH nanosheet and GO nanosheet, and Co—Ni. It was a structure of LDH nanosheets and rGO nanosheets, and a structure of Co-Ni LDH nanosheets and GO nanosheets.

XRD patterns A and B in FIG. 9 show the results of the sample of Comparative Example 6 and the sample of Example 5, respectively. XRD patterns A and B in FIG. 10 show the results of the sample of Comparative Example 8 and the sample of Example 7, respectively. Index 00l shown in FIGS. 9 and 10 is a basic orientation plane of the _{structure, L 100} and _{L 110} are plane diffraction peak from LDH nanosheets.

  Neither the XRD pattern of FIG. 9 nor FIG. 10 showed the peak which the LDH nanosheet or the graphene oxide aggregated. This suggests that the structures obtained in Examples 5 and 7 and Comparative Examples 6 and 8 are uniform superlattice structures that do not have aggregated LDH nanosheets or graphene oxide.

  According to the XRD pattern A of FIGS. 9 and 10, the interlayer distance of the structures of Comparative Example 6 and Comparative Example 8 is about 1.2 nm (an error between 1.1 nm and 1.3 nm was observed). there were. Considering that the crystallographic thicknesses of Co-Al LDH nanosheet / Co-Ni LDH nanosheet and GO nanosheet are 0.48 nm and 0.83 nm, respectively, the theoretical interlayer distance is about 1.31 nm. (0.48 nm + 0.83 nm).

  The interlayer distances (1.1 nm to 1.3 nm) of the structures of Comparative Example 6 and Comparative Example 8 both include a slight error with respect to the theoretical interlayer distance (1.3 nm). Agreed well. This error is considered because the interlayer distance of the structure is affected by electrostatic interaction and the amount of water in the interlayer space.

  When a GO nanosheet is laminated with a Co—Al LDH nanosheet / Co—Ni LDH nanosheet by electrostatic interaction, the interlayer distance of the structure tends to shrink depending on the degree of oxidation of the GO nanosheet. That is, the interlayer distance of the structure can be adjusted by controlling the surface charge. In the composites of Patent Document 1 and Non-Patent Document 1, the interlayer distance (about 2.9 nm) does not match the results of Comparative Example 6 and Comparative Example 8 at all, and LDH nanosheets and GO nanosheets are alternately laminated. It turns out that it cannot be said.

  According to the XRD pattern B of FIGS. 9 and 10, the interlayer distance between the structures of Example 5 and Example 7 was 0.9 nm. Considering that the crystallographic thicknesses of Co-Al LDH nanosheet / Co-Ni LDH nanosheet and rGO nanosheet are 0.48 nm and 0.4 nm, respectively, the theoretical interlayer distance is 0.88 nm. Become.

  The interlayer distance (0.9 nm) of the structures of Example 5 and Example 7 matched very well with the theoretical interlayer distance (0.88 nm). Even if the types of metal ions in the LDH nanosheet are different, the interlayer distance between the structures is always constant, so that it is easy to design a structure having high ion diffusion and high charge transport efficiency.

FIG. 11 is a diagram showing a TEM image (A), a high resolution image (B), and an electron diffraction pattern (C) of the sample of Example 5.
12 is a diagram showing a TEM image (A), a high resolution image (B), and an electron diffraction pattern (C) of the sample of Example 7. FIG.

  Samples for TEM of Example 5 and Example 7 are a structure of Co-Al LDH nanosheet and rGO nanosheet deposited on a microgrid, and a structure of Co-Ni LDH nanosheet and rGO nanosheet, respectively. is there. The TEM images (A) in FIGS. 11 and 12 show that the structures of Examples 5 and 7 have a fibrous appearance.

  According to the high-resolution images (B) of FIGS. 11 and 12, it can be seen that the structures of Example 5 and Example 7 are superlattice structures in which bright regions and dark regions are alternately repeated. . These bright and dark regions suggest LDH nanosheets and rGO nanosheets, respectively.

The electron diffraction patterns (C) of FIGS. 11 and 12 show in-plane diffraction rings (L ₁₀₀ and L ₁₁₀ ) of LDH nanosheets and graphene in-plane diffraction rings (G ₁₀₀ and G ₁₁₀ ) of rGO nanosheets. This suggests that in the superlattice structures of Example 5 and Example 7, the LDH nanosheet and the rGO nanosheet are closely stacked on a microscopic field scale.

  FIG. 13 is a diagram showing element mapping of the sample of Example 5.

  The sample for EDS is a structure of Co—Al LDH nanosheets and rGO nanosheets deposited on a microgrid. The portions shown bright in FIG. 13 show the distribution of Al, Co, and C, respectively. Each elemental mapping is related to the spatial arrangement, indicating that LDH nanosheets and rGO nanosheets are uniformly stacked at the nanometer level, and that the structure of Example 5 is a superlattice structure. Show. Although not shown, the same result was obtained for the structure of Example 7, and thus it was found that the structure of Example 7 was also a superlattice structure. From the above, it is suggested that in the production method of the present invention, by using an aprotic polar solvent as the dispersion medium of the anionic solution, a good superlattice structure can be obtained without being affected by impurities.

  FIG. 14 is a diagram showing an XRD pattern of the sample of Comparative Example 9.

  The sample of Comparative Example 9 was a structure of Co—Al LDH nanosheets and GO nanosheets. XRD patterns A and B in FIG. 14 show the results of a structure having an LDH / G ratio of 5.0 and a structure having an LDH / G ratio of 4.0, respectively. According to FIG. 14, in any XRD pattern, a diffraction peak of Co—Al chlorine type (or carbonate type) LDH in which Co—Al LDH nanosheets aggregated was observed in addition to the diffraction peak caused by the structure. From this, it can be seen that the structure of Comparative Example 9 is a non-uniform superlattice structure including agglomerated LDH nanosheets, and a uniform superlattice structure in which LDH nanosheets and GO nanosheets are alternately stacked. In order to obtain a body, it is suggested that the LDH / G ratio is preferably less than 4.

  Here, the mass ratio in the superlattice structure of the LDH nanosheet and the rGO nanosheet was examined.

<Basic information of LDH>
Space group: R-3m (No. 166)
Crystal system: rhombus symmetry Lattice constant: a = 0.31 nm, c = 2.67 nm (when calculated with hexagonal crystal)
<Basic information on graphite>
Space group: P6 ₃ mc (No. 186)
Crystal system: Hexagonal crystal Lattice constants: a = 0.25 nm, c = 0.67 nm

<In-plane unit lattice area>
LDH: 0.31 × 0.31 × sin 120 ° = 8.32 × 10 ⁻² nm ²
Graphite: 0.25 × 0.25 × sin 120 ° = 5.41 × 10 ⁻² nm ²

<Charge density per unit cell area in plane>
LDH: 0.33e / (8.32 × 10 ⁻² nm ² ) = 3.97 enm ⁻²
Graphene oxide: (0.15 + 0.075) e / (5.41 × 10 ⁻² nm ² ) = 4.16 enm ⁻²
For simplicity, it is assumed that graphite is oxidized with a functional group containing 30% oxygen, half of the functional group is OH (ie, 0.15e), and the other half is COOH (ie, 0 0.075e).
The charge density of LDH was close to that of graphene oxide, and this result was in good agreement with the zeta potential result.

<Molar mass>
Co-Al nitrate type ^{_{LDH: [Co 2+ 2/3 Al 3+}} 1/3 (OH) 2] [NO 3 - 1/3 · 0.5H 2 O] molar mass = 112.2
Co-Ni nitrate type ^{_{LDH: [Co 2+ 1/3 Ni 2+}} 1/3 CO 3+ 1/3 (OH) 2] [NO 3 - 1/3 · 0.5H 2 O] molar mass = 122.8
Graphite: molar mass of 2 carbon atoms = 24

<Mass ratio>
Based on the precursor compound, the concentration of the LDH nanosheet and the GO nanosheet was calculated, and an ideal mass ratio in the superlattice structure was obtained. The mass ratio (LDH / G) of the layered double hydroxide mass (LDH) corresponding to the mass of each LDH nanosheet to the mass (G) of graphite as rGO nanosheet in the superlattice structure is as follows: Calculated.
LDH / G ratio of superlattice structure of Co-Al LDH nanosheet and rGO nanosheet = 5.41 × 10 ⁻² × 112.2 / 8.32 × 10 ⁻² × 24 = 3.04
LDH / G ratio of superlattice structure of Co-Ni LDH nanosheet and rGO nanosheet = 5.41 × 10 ⁻² × 122.8 / 8.32 × 10 ⁻² × 24 = 3.33

  From the above results, in order to obtain a superlattice structure that is well matched and laminated alternately without aggregation, the ratio of the mass of LDH nanosheets to the mass (G) of rGO nanosheets in the superlattice structure (LDH It was found that / G) is preferably 3 or more. Here, the mass of the corresponding graphite is used as the value of G in the expression LDH / G of the value of this ratio, and the mass of the corresponding layered double hydroxide is used as the value of LDH.

  FIG. 15 is a diagram showing an SEM image (A) and electrochemical characteristics (B) to (D) of the sample of Reference Example 1.

The samples for SEM and electrochemical properties were both films consisting of Co—Al LDH plates densely deposited on ITO glass (referred to as Co—Al LDH plate films). FIG. 15A shows that a Co—Al LDH plate film was formed on ITO glass. FIG. 15B is a diagram in which a potential region of −0.2 V to 0.5 V (vs. Ag / AgCl) is swept in KOH (1 M) at various scanning speeds (30, 50, 100 mV / s). It is a click voltammetry (CV) curve. According to FIG. 15 (B), the CV curve showed an oxidation / reduction peak near 0.1V. Since Al ³⁺ is inactive, oxidation / reduction corresponds to the Faraday reaction of Co ²⁺ . More specifically, the anode peak near 0.1 V is based on the oxidation of Co (OH) ₂ to CoOOH, and the cathode peak is based on the reverse process. The Faraday reaction between CoOOH and CoO ₂ is expected to occur at a high potential of 0.4V or higher.

  FIG. 15C shows the electrochemical impedance spectra at potentials of 0 V and 0.1 V in the Cole-Cole (Nyquist) plot format. Z ′ and Z ″ are the real part and imaginary part of the impedance, respectively. Each data point is measured at a specific frequency (f), and the left side of the drawing corresponds to the high frequency side. The Cole-Cole plot measured at both 0.1V and 0V forms a semicircle on the high frequency side, indicating that Faraday charge transport is occurring.

FIG. 15D shows the impedance spectrum in the form of a board plot. The magnitude of impedance and phase shift angle versus frequency are plotted on a log scale to show the effect of frequency on capacitive reactance impedance. According to FIG. 15D, the Bode plot shows that the break frequency ( _{fΦ = −45 °} ) is several Hz (the dotted line area in FIG. _15D ). The break frequency further decreased at 0.1 V where there was an oxidation / reduction peak. That is, it was found that the Faraday pseudocapacitance capacitor characteristics of the Co—Al LDH plate film are extremely poor. This can be understood from the fact that the Co—Al LDH plate has high insulation and has a large charge transport resistance.

  FIG. 16 is a diagram showing an SEM image (A) and electrochemical characteristics (B) to (D) of the sample of Reference Example 2.

Both the SEM and the sample for electrochemical characteristics were films (referred to as Co-Ni LDH plate films) made of Co—Ni LDH plates densely packed on ITO glass. FIG. 16A shows that a Co—Ni LDH plate film was formed on ITO glass. FIG. 16B shows a potential region of −0.2 V to 0.5 V (vs. Ag / AgCl) in KOH (1M) at various scanning speeds (10, 20, 30, 50, 100 mV / s). It is the cyclic voltammetry (CV) curve swept. According to FIG. 16 (B), the CV curve showed an oxidation / reduction peak in the vicinity of 0.3V. The oxidation / reduction peak corresponds to the Faraday reaction of Co ²⁺ and Ni ²⁺ . The potential of the reduction peak was slightly higher than that of the Co—Al LDH nanosheet of Reference Example 1 (0.1 V). This is due to the presence of two types of metals that can be oxidized and reduced in the LDH nanosheet.

  FIG. 16C shows the electrochemical impedance spectra at potentials of 0.1 V and 0.3 V in the Cole-Cole plot format. According to FIG. 16C, the Cole-Cole plot measured at 0.3 V forms a semicircle on the high frequency side, indicating that Faraday charge transport occurs.

FIG. 16D shows the impedance spectrum in the form of a board plot. According to FIG. 16D, the Bode plot showed a complex response of the phase shift angle with respect to frequency. This is due to the high insulating properties of the Co—Ni LDH plate, and shows that the break frequency ( _{fΦ = −45 °} ) is several Hz. Again, the Co—Ni LDH plate film was found to be unsuitable for high power capacitors.

  FIG. 17 is a diagram showing electrochemical characteristics (A) to (C) of the sample of Reference Example 4.

  The sample for electrochemical properties was a film consisting of rGO nanosheets densely packed on ITO glass. FIG. 17A shows a potential region of −0.2 V to 0.4 V (vs. Ag / AgCl) in KOH (1M) at various scanning speeds (10, 20, 30, 50, 100 mV / s). It is the cyclic voltammetry (CV) curve swept. According to FIG. 17A, the CV curve has a substantially rectangular shape having no clear oxidation / reduction peak, and matches the characteristics of a typical conductive carbon surface.

  FIG. 17B shows an electrochemical impedance spectrum at a potential of 0.1 V in a Cole-Cole plot format. On the high frequency side, a vertical line representing ideal capacitor behavior was observed. Since no semicircle was seen, it was found that Faraday charge transport did not occur.

FIG. 17C shows the impedance spectrum in the form of a board plot. On the low frequency side, the real part of the impedance reached a finite value, and the imaginary part of the impedance became infinite. This can also be explained by the fact that the phase shift angle is close to -90 ° which represents the ideal capacitor charge and discharge behavior. The change in impedance at an intermediate frequency is a characteristic change that exhibits an apparent corner frequency and transforms from ideal capacitor behavior to a frequency dependent diffusion limited process. The corner frequency ( _{fΦ = −45 °} ) is about 200 Hz (dotted line in FIG. 17C), indicating that much of the stored energy is accessible up to this frequency. That is, it enables energy output on a time scale of 1 second or less.

  18 is a diagram showing electrochemical characteristics (A) to (C) of the sample of Comparative Example 10. FIG.

The sample for electrochemical properties was a film composed of a mixture of aggregates of Co-Al LDH nanosheets and rGO nanosheets densely packed on ITO glass. FIG. 18 (A) shows that the potential region of −0.2 V to 0.5 V (vs. Ag / AgCl) is swept in KOH (1 M) at various scanning speeds (5, 10, 50, 100 mV / s). 2 is a cyclic voltammetry (CV) curve. According to FIG. 18 (A), the CV curve showed an oxidation / reduction peak near 0.1V. Similar to Reference Example 1, the oxidation / reduction is caused by the Faraday reaction of Co ²⁺ .

  FIG. 18B shows electrochemical impedance spectra at potentials of −0.1 V and 0.1 V in the Cole-Cole plot format. According to FIG. 18B, the Cole-Cole plot measured at any potential forms a semicircle on the high frequency side, indicating that Faraday charge transport occurs.

FIG. 18C shows the impedance spectrum in the form of a board plot. According to FIG. 18C, the _break frequency ( _{fΦ = −45 °} ) was 10 Hz (the dotted line area in FIG. 18C) or less. Again, a physical mixture of LDH nanosheets and rGO nanosheets proved unsuitable for high power capacitors.

  FIG. 19 is a diagram showing electrochemical characteristics (A) to (C) of the sample of Example 5.

The sample for electrochemical properties was a film consisting of a structure of Co-Al LDH nanosheets and rGO nanosheets densely packed on ITO glass. FIG. 19A shows the potential region of −0.2 V to 0.5 V (vs. Ag / AgCl) in KOH (1M) at various scanning speeds (10, 20, 30, 50, 100 mV / s). It is the cyclic voltammetry (CV) curve swept. According to FIG. 19A, the CV curve showed an oxidation / reduction peak near 0.1V. Similar to Reference Example 1 and Comparative Example 10, the oxidation / reduction is caused by the Faraday reaction of Co ²⁺ .

  FIG. 19B shows the electrochemical impedance spectra at potentials of 0.1 V and −0.1 V in the Cole-Cole plot format. According to FIG. 19B, the Cole-Cole plot measured at 0.1 V forms a semicircle on the high frequency side, indicating that Faraday charge transport occurs.

FIG. 19C shows the impedance spectrum in the form of a board plot. The break frequency ( _{fΦ = −45 °} ) was several tens of Hz (the dotted line area in FIG. _19C ). This value is compared with the result of the Co—Al LDH plate alone of Reference Example 1 (FIG. 15D) and the result of the physical mixture of the LDH nanosheet and the rGO nanosheet of Comparative Example 10 (FIG. 18C). Then, it turned out that it was 10 times or more larger. The frequency response at a potential of −0.1 V reached the same height as about 100 Hz.

  FIG. 20 shows the electrochemical characteristics (A) to (C) of the sample of Example 7.

The sample for electrochemical properties was a film consisting of a structure of Co-Ni LDH nanosheets and rGO nanosheets densely packed on ITO glass. FIG. 20 (A) shows that the potential region of −0.2 V to 0.4 V (vs. Ag / AgCl) is swept in KOH (1 M) at various scanning speeds (10, 20, 50, 100 mV / s). 2 is a cyclic voltammetry (CV) curve. According to FIG. 20A, the CV curve showed an oxidation / reduction peak near 0.3V. Similar to Reference Example 2, the oxidation / reduction is caused by the Faraday reaction of Co ²⁺ and Ni ²⁺ .

  FIG. 20B shows the electrochemical impedance spectra at potentials of −0.1 V and 0.3 V in the Cole-Cole plot format. According to FIG. 20B, the Cole-Cole plot measured at 0.3 V forms a semicircle on the high frequency side, indicating that Faraday charge transport occurs.

FIG. 20C shows the impedance spectrum in the form of a board plot. The break frequency ( _{fΦ = −45 °} ) was several tens of Hz (the dotted line region in FIG. 20C). This value was found to be much larger when compared with the result of the Co—Ni LDH plate alone of Reference Example 2 (FIG. 16D). The frequency response at a potential of −0.1 V reached the same height as about 100 Hz.

  According to FIGS. 15 to 20 described above, by configuring the superlattice structure of the present invention in which highly conductive rGO nanosheets and insulating LDH nanosheets are alternately laminated, the overall conductivity is increased. It was found that the output performance was remarkably improved. In addition, the electrons generated by the Faraday reaction of the oxidizable / reducible LDH nanosheets are effectively concentrated in the adjacent rGO nanosheets and quickly transported to the external circuit, thus dramatically increasing the capacity charge and discharge capability. be able to. Furthermore, since an ultrahigh-speed response of about 100 Hz, which is almost equal to an EDL capacitor based on an rGO nanosheet, is possible, the structure of Example 5 is a superlattice structure of a Co—Al LDH nanosheet and an rGO nanosheet. This suggests a superlattice structure of 7 Co—Ni LDH nanosheets and rGO nanosheets.

  FIG. 21 is a diagram showing the results of constant current charge / discharge (CD) measurement using the samples of Reference Example 4, Example 5, and Example 7.

  Samples for CD measurement of Reference Example 4, Example 5 and Example 7 were respectively a film made of rGO nanosheets densely packed on ITO glass, a film made of a structure of Co-Al LDH nanosheets and rGO nanosheets, And it was the film | membrane which consists of a structure of a Co-Ni LDH nanosheet and an rGO nanosheet. 21A to 21C show the measurement results of the samples of Reference Example 4, Example 5, and Example 7, respectively.

  CD measurement was performed in a current density of 5 A / g and a potential range of 0 V to 0.4 V. When FIG. 21A is compared with FIGS. 21B and 21C, the capacity of the superlattice structures of Example 5 and Example 7 is 5-6 compared to that of the rGO nanosheet of Reference Example 4. I found it twice as big. This is also an effect obtained by combining the rGO nanosheet with the LDH nanosheet that can be oxidized and reduced.

  The specific capacity of the rGO nanosheet calculated from FIG. 21 (A) was about 100 F / g. The specific capacities of the structure of Example 5 and the structure of Example 7 calculated from FIGS. 21B and 21C were about 450 F / g and about 650 F / g, respectively.

  FIG. 22 is a diagram illustrating the scan rate dependence of the specific capacity of the samples of Reference Example 4, Example 5, Example 7, and Comparative Example 10.

  Samples for measurement of Reference Example 4, Example 5, Example 7 and Comparative Example 10 were respectively a film made of rGO nanosheets densely packed on ITO glass, and a structure of Co-Al LDH nanosheets and rGO nanosheets. A film made of a structure of a Co—Ni LDH nanosheet and an rGO nanosheet, and a film made of a mixture of an aggregate of Co—Al LDH nanosheets and an aggregate of rGO nanosheets. Curves A to D in FIG. 22 are measurement results of samples of Reference Example 4, Comparative Example 10, Example 5, and Example 7, respectively.

  The specific capacity of the mixture of Comparative Example 10 and the structures of Examples 5 and 7 decreased as the scanning speed increased, whereas the specific capacity decrease of the structures of Examples 5 and 7 was the ratio of the mixture of Comparative Example 10 It was more gradual than capacity reduction.

  Comparing the results of Example 5 and Example 7, it was found that the specific capacity of the structure of Example 7 was larger than that of Example 5 at any scan speed. This indicates that it is preferable to use LDH nanosheets containing Co and Ni as M1 elements and Co as a substitute for inert Al as M2 elements.

  FIG. 23 is a diagram showing the behavior of the volume of the sample of Example 7.

  The sample for measurement is a film made of a structure of Co—Ni LDH nanosheets and rGO nanosheets densely packed on ITO glass. FIG. 23A shows constant current discharge curves at various current densities (2, 5, 10, 20, 30 A / g). FIG. 23B shows the dependency of the specific capacity on the discharge current density. FIG. 23C shows the cycle number dependency of capacity at a current density of 5 A / g.

  According to FIG. 23B, it was found that the structure of Example 5 maintained a high specific capacity exceeding 500 F / g up to a maximum discharge current density of 30 A / g. According to FIG. 23C, the structure of Example 5 retained a specific capacity of 97% even after 2000 cycles and had excellent retention characteristics. These facts also indicate that the superlattice structure according to the present invention is suitable as an electrode material for pseudocapacitance capacitors and supercapacitors.

  Since the superlattice structure of the present invention has a high specific capacity and a high charge transport efficiency, it is used as an electrode material for pseudocapacitance capacitors, supercapacitors and the like.

100 superlattice structure 110 double hydroxide nanosheet 120 reduced graphene oxide nanosheet

Claims (20)

A superlattice structure in which double hydroxide nanosheets containing M1 ²⁺ ions and M2 ³⁺ ions and reduced graphene oxide nanosheets are alternately laminated,
The M1 element of the M1 ²⁺ ion is a metal element selected from at least one selected from the group consisting of Co, Fe, Ni, Mn, Cu and Zn,
The M2 element of the M2 ³⁺ ion is a metal element selected from at least one selected from the group consisting of Al, Cr, Mn, Fe, Co, Ni, and Ga.
A superlattice structure in which an interlayer distance is in a range of 0.8 nm or more and less than 1.3 nm.   The superlattice structure according to claim 1, wherein the M1 element is Co and the M2 element is Al.   The superlattice structure according to claim 1, wherein the M1 element is Co and Ni, and the M2 element is Co.   The superlattice structure according to claim 1, wherein a thickness of the double hydroxide nanosheet is in a range of 0.48 nm to 1.0 nm.   The superlattice structure according to claim 1, wherein a thickness of the reduced graphene oxide nanosheet is in a range of 0.33 nm to 0.83 nm.   The superlattice structure according to claim 1, wherein the interlayer distance is in a range of 0.8 nm or more and less than 1.1 nm. The double hydroxide nanosheet is represented by a general formula [M1 ²⁺ _1-x M2 ³⁺ _x (OH) ₂ ] ^{x +} (x is a real number of 0 <x ≦ 1/3). Superlattice structure. The double hydroxide nanosheet represented by the general formula _{^{[M1 2+ 1-x M2 3+}} x (OH) 2] [Z n- x / n · mH 2 O] (Z is an anion, n represents the anion Z Wherein x is a real number of 0 <x ≦ 1/3, and m is a real number of 0 <m <1). Item 8. The superlattice structure according to Item 7.   The superlattice structure according to claim 1, wherein the reduced graphene oxide nanosheet is reduced after being peeled off from the graphene oxide. Using the mass (G) of graphite as a precursor as the mass of the reduced graphene oxide nanosheet, the layer containing the M1 ²⁺ ion and the M2 ³⁺ ion as a precursor as the mass of the double hydroxide nanosheet When the double hydroxide mass (LDH) is used, the ratio (LDH / G) of the layered double hydroxide mass (LDH) to the graphite mass (G) is 3 or more and less than 4. Item 2. The superlattice structure according to Item 1. It is a manufacturing method of the superlattice structure according to any one of claims 1 to 10,
A cationic solution in which double hydroxide nanosheets containing M1 ²⁺ ions and M2 ³⁺ ions are dispersed in a first aprotic polar solvent, and reduced graphene oxide nanosheets in at least a second aprotic polar solvent Mixing and stirring the dispersed anionic solution. In the mixing and stirring step, the M1 ²⁺ ion and the M2 ³⁺ ion that are the precursor of the double hydroxide nanosheet with respect to the mass (G) of the graphite that is the precursor of the reduced graphene oxide nanosheet are contained The method of claim 11, wherein the ratio (LDH / G) of the layered double hydroxide mass (LDH) is 3 or more and less than 4. 13.   The method according to claim 11, wherein in the anionic solution, the reduced graphene oxide nanosheet is dispersed in a mixed solvent of the second aprotic polar solvent and water.   The volume ratio (H / F) of the water (H) to the second aprotic polar solvent (F) in the mixed solvent is in a range of 0 or more and 0.5 or less. Method.   The method of claim 11, wherein the first aprotic polar solvent is selected from the group consisting of formamide, dimethyl sulfoxide, methylformamide, and dimethylformamide.   12. The method of claim 11, wherein the second aprotic polar solvent is selected from the group consisting of formamide, dimethylsulfoxide, methylformamide, and dimethylformamide.   The method according to claim 11, wherein in the mixing and stirring, the anionic solution is added at a rate of 1 mL / min to 10 mL / min while stirring the cationic solution at room temperature.   The method according to claim 11, wherein in the mixing and stirring, the cationic solution is added at a rate of 1 mL / min to 10 mL / min while stirring the anionic solution at room temperature.   Prior to the mixing and stirring step, the method further includes a step of preparing an anionic solution by adding a reducing agent to a solution in which graphene oxide nanosheets are dispersed in at least a second aprotic polar solvent and then heating the solution. Item 12. The method according to Item 11.   It is an electrode material which consists of a superlattice structure, Comprising: The said superlattice structure is an electrode material which is a superlattice structure in any one of Claims 1-10.