KR100759895B1 - Methods for Manufacturing nickel oxide nanotube by anodic aluminum oxide template - Google Patents

Abstract

The present invention relates to a method for producing nickel nanotubes using an anodized aluminum oxide ( AAO ) template.

Unlike the conventional method of manufacturing metal nanotubes, the method for preparing nickel nanotubes according to the present invention uses only distilled water, nickel precursors and AAO templates under mild conditions, and maintains the shape of the nanotubes by adsorbing the nickel precursor onto the surface of the AAO template. By uniformly drying the nanotubes can be easily obtained.

Nickel nanotubes made according to the manufacturing method of the present invention can be utilized as an economic hydrogen storage or the electrode of a lithium secondary battery or as a storage source for automobiles and other mobile energy.

Nickel, Nanotube, Template, Solvent, Hydrogen Storage, Secondary Battery, Electrode Material

Description

Method for manufacturing nickel oxide nanotube by anodic aluminum oxide template

1 is a SEM photograph of a nickel nanotube according to an embodiment of the present invention.

2 is a TEM photograph of nickel nanotubes according to an embodiment of the present invention.

Figure 3 is a model showing a vacuum drying apparatus for producing a nickel nanotube of the present invention.

Figure 4 is a graph showing the X-ray diffraction of the nickel nanotubes according to an embodiment of the present invention.

5 is a SEM photograph of the nickel nanorods prepared according to the comparative example of the present invention.

6 is a TEM photograph of nickel nanorods prepared according to a comparative example of the present invention.

7 is a simulation model diagram of LiNiO ₂ nanotubes by computer simulation.

8 is a charge / discharge test according to the potential change of the secondary battery using the lithium-added nickel nanotube prepared in Example 3

[Description of Drawing Reference]

One… Vacuum pump 2.. Cooling trap

3... Cock valve 4.. Decompression Dryer

5... sample

The present invention relates to a method for producing nickel nanotubes which can be economically and efficiently produced using only distilled water, anodized aluminum oxide (AAO) template and nickel precursor.

Synthesis of nanostructures using anodized aluminum oxide (hereinafter abbreviated as "AAO") template, the synthesis of carbon nanotubes using chemical vapor deposition on AAO templates, the formation of sodium nanotubes on the inner walls of AAO templates, LiMn using AAO templates until ₂ O ₄ nanowires are synthesized such, there has been a lot of attempts.

In general, one of the advantages of the method (synthesis method) of manufacturing a nanostructure using the AAO template is that the shape of the fabricated nanostructure is straight, has a uniform cylinder shape, and has a high density. AAO templates do not directly participate in the formation of nanotubes / nanorods, but they do affect the physical appearance of nanostructures.

The nanostructures can be utilized in various industrial fields for various purposes, and the typical use is as an energy storage body for storing hydrogen.

Hydrogen is an infinitely clean resource that can be obtained from water on Earth and is recycled back to water after combustion, with little potential for exhaustion. As such, hydrogen (energy) is a clean energy that does not generate any pollutants other than water during combustion. Therefore, hydrogen (energy) can be used in almost all fields such as various means of transportation or power generation systems.

However, one problem with the use of such hydrogen energy is that a convenient, economical and safe hydrogen storage system has not yet been developed.

As one of the traditional hydrogen storage methods, there is a physical method of compressing and storing hydrogen in a high pressure container at more than 100 atmospheres, but it is very dangerous for safety to mount such a high pressure container on a vehicle. Another physical method of storing hydrogen is to store the hydrogen at a cryogenic temperature below the boiling point (20.3 K), which has the advantage of storing a large amount of hydrogen by significantly reducing the storage volume of hydrogen. It is very disadvantageous from an economic point of view because an auxiliary device (freezing device) is required to maintain the cryogenic temperature.

On the other hand, the chemical storage method using the hydrogen storage alloy has the advantage that the storage efficiency of the hydrogen is high, but when the storage and release of hydrogen repeatedly carried out deformation of the hydrogen storage alloy due to impurities in the hydrogen and thus hydrogen storage There is a problem that the capacity decreases over time. In addition, since the alloy is used as a hydrogen storage medium, the weight per unit volume increases, which makes it difficult to mount and use the vehicle.

Another method of storing hydrogen is to adsorb and store gaseous hydrogen in a solid material. Among the adsorption methods, various reports on the efficiency of hydrogen storage using carbon nanotubes or nanostructured carbon materials show hydrogen storage efficiencies well above 10% by weight, but these results still lack reproducibility. Many studies are in progress.

Therefore, a lot of research is currently being conducted to develop a hydrogen storage method that has a hydrogen storage efficiency of 6.5 wt% or more, which is a target of the US Department of Energy (DOE) hydrogen storage efficiency, and stability and economy without the above-mentioned problems. .

On the other hand, as a lithium secondary battery positive polarization material that is a source of energy for portable electronic information communication devices and small devices, it is an oxide to which lithium can enter and exit, including a layered structure or a tunnel-shaped space in its crystal. LiCoO ₂ , LiNiO ₂ , LiMn _{There is a 2} O ₄ system. Among them, LiNiO ₂ system has the largest capacity (180> mAh / g) among the three positive electrode materials, as well as excellent repeatability and stability against electrolyte and environmentally friendly characteristics. Lithium nickel-based oxide is superior in characteristics and price compared to lithium cobalt-based oxide, which is currently spreading in the market. Therefore, it is expected that demand will soon be generated in view of rapid miniaturization and light weight of electronic components. It is expected to be a suitable power source for the equipment. Moreover, lithium nickel-based oxides are superior to other positive electrode materials in terms of energy capacity and density, and their occupancy area is small, and thus they may be used as power sources for next-generation electric vehicles as well as power supplies for small electronic devices. If the safety and ease of manufacture are resolved prior to commercialization, it will be replaced by the positive electrode material of the lithium ion battery currently used, and will be extended to the lithium polymer battery, the next generation secondary battery. Until now, there have been no examples of using nanotubes as positive electrode materials for secondary batteries.

One of the technical problems of the present invention is to provide a method for efficiently producing nickel nanotubes having uniform nano-sized pores under mild conditions using only distilled water, nickel precursors, and anodized aluminum templates. have.

Another technical problem to be achieved by the present invention is to provide a positive polarization material of a lithium secondary battery having excellent charge and discharge results using nickel nanotubes containing lithium manufactured by the manufacturing method.

The present invention for solving the above problems is an immersion process soaking the AAO template in an aqueous solution of a nickel precursor so that the nickel precursor is adsorbed to the AAO template; A vacuum drying process of separating the AAO template to which the nickel precursor is adsorbed in an aqueous solution and then drying under reduced pressure to remove the remaining portions except the nickel precursor adsorbed to the AAO; An oxidation process of oxidizing the nickel precursor adsorbed on the surface by heat-treating the AAO template to which the dried nickel precursor is adsorbed; Dissolution process of soluble litter only AAO template the AAO template the nickel oxide precursor is adsorbed to the NaOH or KOH aqueous solution; A filtering step of solid-liquid separation between the AAO solution produced in the dissolution process and the nickel nanotubes in a solid form; Drying process of drying nickel nanotubes separated from AAO; And a calcination process of removing impurities by calcining the nickel nanotubes from which moisture is removed during the drying process.

As the nickel precursor used in the production of nickel nanotubes according to the present invention, Ni (NO ₃ ) ₂ · 6H ₂ O was used in this embodiment, but the nickel oxide was adsorbed on an AAO template to dry the nickel oxide. It may be formed, and any one that can be dissolved in distilled water is not limited thereto. That is, it is obvious to those skilled in the art that other nickel salts such as NiCl ₂ H ₂ O may also be used in the production of nickel nanotubes.

As the AAO template, it is preferable to use an AAO template having a pore size of 180 to 250 nm and a thickness of 40 to 80 μm. Although not specifically described in the examples, the use of a template with an average porosity of 180 nm or less showed the shape of a rod composed of nano-sized particles without properly forming the tube. On the other hand, the AAO template with a pore size of 250 nm or more is meaningless because the pore size is too large to form a nanostructure, particularly a nanostructure for use as an energy storage body.

The amount of nickel precursor used in the immersion process is preferably used 10 ~ 50mmol per 0.174g of AAO template. If the amount of the nickel precursor is too small, it will not be sufficiently adsorbed on the AAO template. If the amount is too large, the excess nickel precursor is removed, which does not affect the production of nanotubes, but the efficiency is lowered from an economic point of view. Nickel precursor is used by dissolving in distilled water to make the liquid phase, in this case, it is preferable to use the minimum amount that can dissolve the nickel precursor, it is generally preferred to use an aqueous solution of 1 ~ 5M concentration. If the concentration of the aqueous solution of the nickel precursor is too thin, it may not be effectively adsorbed on the AAO template, and there is a fear that impurities present in the purified water in a small amount affect the nanotube formation. The immersion process is preferably made 1 to 5 hours at room temperature.

The reduced pressure drying process is preferably made for 2 to 5 hours in the temperature range of 40 ~ 80 ℃. If the drying temperature is too low, or the drying time is too short, drying does not occur sufficiently. As can be seen in the comparative example, the moisture remaining in the AAO template is dried under reduced pressure and oxidized to produce nickel nanotubes, and if the moisture is not sufficiently dried under reduced pressure, nanotubes are not formed and nanorods are formed. Since the nanotubes are hollow and have a large surface area, they have a large effective area for physical adsorption, while nanorods can react only on the surface of the rod, and thus have a lower application range than nanotubes. High drying temperature or long drying time at reduced pressure drying does not affect the production of the nanotube shape, but there is a problem that the efficiency is lowered.

The oxidation process for oxidizing the nickel precursor is preferably carried out for 1 to 4 hours in the temperature range 80 ~ 150 ℃ in the presence of oxygen to sufficiently oxidize the adsorbed nickel precursor. The term "in the presence of oxygen" means that there must be oxygen to react with the nickel precursor during the heat treatment. Therefore, in order to supply oxygen, the oxygen gas may be filled in the dryer to be heat treated, but economical burden is required, so simply heat treatment in the presence of air is sufficient.

The concentration of NaOH or KOH aqueous solution used in the dissolution process is preferably 1 ~ 5M aqueous solution, it is preferable to use an aqueous solution of 50mL or more per 0.174g of AAO to sufficiently dissolve the AAO template.

The AAO template, which is dissolved and dissolved in solution, is separated from the nickel nanotubes that remain in the solid state and filtered. In order to prevent the NaOH or KOH solution in which the AAO template is dissolved, remain in the nanotubes, it is sufficiently washed with purified water during the filtering process.

Nickel nanotubes obtained through the filtering process according to the present invention is dried by treating for 1 to 4 hours within the range of 80 ~ 150 ℃ in order to remove this because a small amount of water remaining during filtration. After drying, calcining for 2 to 3 hours in the 450 ~ 550 ℃ temperature range can not only moisturize more efficiently, but also remove the remaining impurities.

The nickel oxide nanotubes obtained through the drying process and the calcination process are immersed in a solution in which a lithium precursor is dissolved in distilled water, and then dried under reduced pressure by separating only lithium nanoparticles adsorbed. Lithium-adsorbed nickel nanotubes are oxidized by heat treatment for 1 to 4 hours in the range of 80 to 150 ° C in the presence of oxygen, and then calcined at 450 to 550 ° C electric furnace for 2 to 3 hours. Can be prepared.

The lithium precursor may be a hydroxide, halide, nitrate, carbonate or sulfate of lithium, and the molar ratio of nickel nanotube: lithium precursor is preferably 1: 0.1. More preferably, the lithium precursor is added in a molar ratio of 1: (1-3) to the nickel nanotubes. Lithium-added nickel nanotubes according to the present invention can be applied as a lithium ion secondary battery material.

Hereinafter, with reference to the accompanying drawings and the following examples will be described in detail the configuration, operation, and effects of the present invention. Here, the following examples are merely illustrative, and the protection scope of the present invention should not be reduced or limited to the scope of the following examples.

Example 1 Preparation of Nickel Nanotubes

Aldrich's Nickel (II) nitrate hexahydrate and crystal (Ni (NO ₃ ) ₂ · 6H ₂ O) were used as precursors for nickel nanotubes, and Whatman's anodisc 47 was used as a template for nanotubes. The main component of Anodisc 47 is aluminum oxide (anodisc aluminum oxide, AAO). The major physical properties of Whatman's anodisc 47 are shown in Table 1.

First, 6.32 g of nickel (II) nitrate hexahydrate was dissolved in 10 g of distilled water, and 0.174 g of AAO template was soaked in the mixed solution for 2 hours. The AAO template was then separated from the solution and dried for 4 hours in a reduced pressure dryer at 40 ° C. to remove the AAO template and the non-adsorbed nickel (II) nitrate solution. The dried AAO template was dried for 2 hours at a temperature of 100 ℃ under an air atmosphere to sufficiently oxidize. In order to obtain only nickel nanotubes from the dried AAO template, the alumina membrane dissolved in NaOH solution was removed several times with distilled water after immersion in 1M NaOH solution for 3 hours. The nickel nanotubes obtained after the filtering were dried in an air atmosphere at a temperature of 100 ° C. for 3 hours, and the dried nickel nanotubes were calcined at an electric furnace under a 500 ° C. air atmosphere for 2 hours to form a wall of tubes with small nanoparticles. Nickel nanotubes were prepared.

1 and 2 are views showing SEM (Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy) photographs of nickel nanotubes prepared according to the manufacturing method of the present embodiment. Nanotubes have many nano-sized small particles that form a wall of the tube, have a certain size, and have a very large surface area, which is very advantageous for storing hydrogen.

Figure 3 is a model showing a pressure reduction drying apparatus for producing a nickel nanotube of the present embodiment. The cooling trap is filled with liquid nitrogen to prevent contamination of the vacuum pump during the vacuum drying, and the nickel-adsorbed AAO template is placed in the vacuum drying chamber and the vacuum pump is operated to remove the non-adsorbed nickel precursors in the AAO template.

Figure 4 shows the XRD (X-Ray Diffraction) results of the nickel nanotubes made according to the manufacturing method of the embodiment, it can be seen that the prepared nickel nanotubes have a structure of NiO.

Comparative Example: Preparation of Nickel Nanorods

Nickel precursors were Nickel (II) nitrate hexahydrate and crystal (Ni (NO ₃ ) ₂ · 6H ₂ O) from Aldrich, and Whatman's anodisc 47 was used as a template for the nanorods. First, 6.32g of Nickel (II) nitrate hexahydrate was dissolved in 10g of distilled water, and 0.174g of AAO template was soaked in the mixed solution for 2 hours. Thereafter, the AAO template to which the nickel precursor was adsorbed was dried at room temperature for 2 hours, and then the dried AAO template was dried at 100 ° C. under an air atmosphere for 2 hours to sufficiently oxidize. To obtain only nickel nanorods from the dried AAO template, after dipping in 60 mL of 1M NaOH solution for 3 hours, the alumina membrane dissolved in NaOH solution was repeatedly removed several times with distilled water. The nickel nanorods obtained after the filtering were dried for 3 hours in a dryer at 100 ° C. under an air atmosphere. The dried nickel nanorods were calcined in an electric furnace under a 500 ° C. air atmosphere for 2 hours to prepare nickel nanorods made of small nanoparticles.

5 and 6 show SEM (Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy) photographs of the nickel nanorods made according to the manufacturing method of the comparative example, and the AAO template to which the nickel precursor is adsorbed as shown in the photographs. When dried at room temperature, many nano-sized flakes, not the shape of nanotubes, were found to form nanorods.

Example 2: Nickel Nanotubes with Lithium Added

The nickel nanotubes prepared in Example 1 were immersed in an aqueous Lithium nitrate (LiNO ₃ ) solution for 2 hours, and only lithium-adsorbed nickel nanotubes were separated and dried in a reduced pressure dryer maintained at 40 ° C. for 4 hours. Afterwards, the lithium-adsorbed nickel nanotubes were dried for 3 hours in a dryer at 100 ° C under an air atmosphere, and the lithium nanotubes were calcined for 2 hours in an electric furnace under a 500 ° C air atmosphere. Added nickel nanotubes were prepared.

Lithium-added nickel nanotubes prepared by the above method were simulated by molecular dynamic method through energy minimization.

FIG. 7 shows simulation results of LiNiO ₂ nanotubes through computer simulation, and it can be seen that lithium ions exist in the space in the nickel oxide nanotubes.

Example 3 Capacitance Experiment of Secondary Battery Using Lithium-Added Nickel Nanotubes

Lithium-added nickel oxide nanotubes prepared in Example 2 were mixed with Super P Black and PVDF (Polyvinylidine Difluoride) at a weight ratio of 85: 10: 5, and NMP (4% by weight) was used as a binder to obtain a concentration of 4 wt% of PVDF. N-Methyl-2-Pyroridone) was used to dissolve the mixture to prepare an electrode mixture and cross-sectional coating on a 10 μm thick copper thin film. After application, the coating was dried at 100 ° C. for 10 hours, cooled to room temperature, and pressed to a thickness of about 70% at 60 μm at 40 μm. A 2032 cell was constructed using a 10 mm diameter disk and a lithium counter electrode (FMC) and a separator (Tonen).

Charge and discharge characteristics were investigated by capacitive experiment on the lithium secondary battery manufactured by the above method, and the results are shown in FIG. 8. The compound prepared in Example 2 could not clearly determine the presence or absence of Li on the XRD, and only a diffraction pattern of NiO could be obtained (data not shown). If lithium is not present in the nanotubes of Example 2, the charging / discharging phenomenon will not appear in the secondary battery charging / discharging experiments. Could.

As can be seen in Figure 8, the maximum voltage of the secondary battery was measured at 4.2V, the average voltage was about 3.5V.

According to the present invention, nanotubes of a certain size may be manufactured under mild conditions using only distilled water, a precursor of nickel metal, and an AAO template.

In addition, according to the nickel nanotube obtained by the production method of the present invention, the specific surface area is very large, it is possible to store hydrogen in a large amount in a relatively small volume and transport it safely. Therefore, it can be used not only as a hydrogen energy storage body but also as an electrode of a lithium secondary battery.

Claims (6)

(A) an immersion process in which the AAO template is immersed in an aqueous solution of the nickel precursor so that the nickel precursor is adsorbed on the AAO template; (B) a reduced pressure drying process of separating the AAO template to which the nickel precursor is adsorbed in an aqueous solution and then drying under reduced pressure to remove the remaining portions except the nickel precursor adsorbed to the AAO; (C) an oxidation process of oxidizing the nickel precursor adsorbed on the surface by heat-treating the AAO template to which the dried nickel precursor is adsorbed in the presence of oxygen; (D) dissolving step of dissolving only the litter AAO template the AAO template the nickel oxide precursor is adsorbed to the NaOH or KOH aqueous solution; (E) a filtering step of solid-liquid separation of the AAO solution produced in the dissolution step and the nickel nanotubes in a solid form; (F) drying process of drying nickel nanotubes separated from AAO; And (G) a calcination process of calcining the nickel nanotubes from which moisture is removed during the drying process. The method of claim 1, The nickel precursor is Ni (NO ₃ ) ₂ · 6H ₂ O The method of manufacturing nickel nanotubes, characterized in that. The method of claim 1, The cathode aluminum oxide template has a pore size (pore size) of 180 ~ 250nm, the thickness of the manufacturing method of nickel nanotubes, characterized in that 40 ~ 80㎛. The method of claim 1, The reduced pressure drying process is a method for producing nickel nanotubes, characterized in that made for 2 to 5 hours in the temperature range of 40 ~ 80 ℃. (A) the ion exchange process of performing ion exchange by addition of a lithium precursor and water respectively into the nickel impregnation nanotubes obtained by the claim 1 by the addition of lithium; (B) a reduced pressure drying process of drying the lithium-added nickel nanotubes under reduced pressure ; And (C) an oxidation process of oxidizing the lithium precursor added to the nickel nanotubes in the above process by heat treatment; (D) calcining process to be calcined at 450 ~ 550 ℃; method of producing a lithium-added nickel nanotubes characterized in that the pass sequentially. A secondary battery comprising the nickel nanotube to which lithium according to claim 5 is added as a positive electrode material.

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