KR101048767B1 - Method for preparing spinel lithium titanium oxide nanotube and its use - Google Patents

Abstract

The present invention relates to a manufacturing method capable of mass-producing spinel lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ) nanotubes in a uniform form, and more specifically, (A) titanium t-butoxide, lithium hydroxide and cetyl. Adding trimethyl ammonium salt into water and mixing uniformly; (B) hydrothermally treating the mixture at a temperature of 60-120 ° C. to produce Li ₄ Ti ₅ O ₁₂ nanoparticles; (C) heat-treating the Li ₄ Ti ₅ O ₁₂ nanoparticles produced by hydrothermal treatment at 300 ~ 500 ℃; And (D) hydrothermally reacting the heat-treated Li ₄ Ti ₅ O ₁₂ nanoparticles in an aqueous alkali solution.

The spinel-structured Li ₄ Ti ₅ O ₁₂ nanotubes prepared by the present invention are not only applicable to lithium ion batteries as electrode materials and large-capacity storage materials, but also as hydrogen-friendly alternative energy storage materials. It is thought that the economic ripple effect is very great by realizing the normal temperature storage of

Nanotube, Lithium Titanium Oxide, Spinel, Hydrogen Storage, Lithium Secondary Battery, Energy Storage Material

Description

Preparation method and use of spinel lithium titanium oxide nanotubes

The present invention relates to a manufacturing method capable of mass-producing spinel lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ) nanotubes in a uniform form and to their use as lithium secondary batteries and hydrogen storage materials.

Most of the energy sources we use today are non-renewable resources such as coal and oil. One of the biggest challenges of the 21st century is undoubtedly the innovative energy storage materials and devices that can be recycled in case of resource depletion [AS Arico et al ., Nature Materials . 2005 , 4, 366]. The storage of energy can be by electrochemical, physical or chemical methods [LF Nazar, Int. J. Inorg. Mater . 2001 , 3, 191; M. Hirshes, Mater. Sci. Eng. B 2004 , 108, 1; A. Zuttel et al. , Int. J. Hydrogen Energy 2002 , 27, 203; R. Strobel et al., J. Power Sources 1999 , 84, 221; MG Nijkamp et al. , Appl. Phys. A 2001 , 72, 619; A. Steinfeld, Int. J. Hydrogen Energy 2002 , 27, 611]. A representative example of the energy storage device by the electrochemical method is a secondary battery, the lithium secondary battery occupies about 30% of the total market size, and is widely used as a power supply device such as mobile phones, notebooks.

In order to be used as an electrode of a lithium secondary battery, the mobility of lithium must be high and the structure of the lithium secondary battery should not change as charging and discharging are repeated. Recently, nanostructures of various structures have been studied as electrode materials. In particular, nanotubes, nanowires and mesoporous structure materials have been widely studied because they are expected to be suitable as electrode materials for lithium secondary batteries because of their large surface area and ease of handling in electrode manufacturing.

Hydrogen is an equal resource that can be obtained from water anywhere on earth, and is an ideal clean resource that does not have to be depleted because it is recycled to water by combustion and does not generate pollutants during combustion [MS Dresselhaus et al ., Nature 2001 , 414, 332]. ]. However, hydrogen is the lightest gas and its boiling point is minus 252.9 ° C, so it is very expensive to use it for high pressure compression or liquefaction like LPG (liquefied petroleum gas) or LNG (liquefied natural gas). Therefore, the development of a safe hydrogen storage system is required to use the ideal hydrogen energy, but still remain at the technical level [A. Zuttel, Materials Today 2003 , 24].

One of the energy storage materials attracting attention as hydrogen storage systems is nanomaterials containing transition metals [Y. Feldman et al., Science 1995 , 267, 222; M. Zelinski et al . , J. Am. Chem. Soc . 1998 , 120, 734; WK Hsu et al . , J. Am. Chem. Soc . 2000 , 122, 10155; YQ Zhu et al. , Chem. Commun . 2001 , 121; M. Nath et al . , J. Am. Chem. Soc . 2001 , 123, 4841; M. Nath et al. , Chem. Commun . 2001 , 2236; RLD Whitby et al., Chem Phys Chem 2001 , 2, 620; YQ Zhu et al. , Chem. Commun . 2001 , 2184; J. Chen et al . , J. Am. Chem. Soc . 2001 , 123, 11813; C. Tang et al . , J. Am. Chem. Soc . 2002 , 124, 14550; J. Chen et al . , J. Am. Chem. Soc . 2003 , 125, 5284; J. Chen et al ., J. Alloys Compd . 2003 , 356-357, 413. This is thought to be due to the potentially large storage capacity and faster hydrogen adsorption and desorption times of nanostructured materials compared to bulk materials [HK Lee et al . , Phys. Rev. Lett . 2006 , 97, 056104; DM Antonelli et al . , Adv. Mater. 2004 , 16, 765]. Recently, there have been many successful results regarding hydrogen storage ability of mesoporous, microporous and nanotubes including titanium as an energy storage material [X. Hu et al . , J. Am. Chem. Soc . 2006 , 128, 11740; SH Lim et al . , Inorg. Chem . 2005 , 44, 4124; DV Bavykin et al., J. Phys. Chem B 2005, 109, 19422; Q. Sun et al . , J. Am. Chem. Soc . 2005, 127, 14582. The tube structure is more advantageous for hydrogen storage due to the faster rate of adsorption and desorption at the surface than other structures.

Since spinel lithium titanium oxide was first known in 1971, the spinel lithium titanium oxide has been attracting much attention as an excellent electrode material or a large storage material because there is no mobility of lithium ions and no structural change of the material during charge-discharge. However, the ability to store hydrogen at room temperature has not been reported until now [A. Guerfi et al., J. Power Sources 2003 , 119-121, 88; EM Sorensen et al. , Chem. Mater . 2006 , 18, 482].

Li ₄ Ti ₅ O ₁₂ is a typical spinel lithium titanium oxide-based compound is mixed by mixing a titanium source and a lithium source such as Li ₂ CO ₃ or LiOH in a solid state and reacted for 12 to 24 hours at 800 ~ 1000 ℃. If the reaction is insufficient at this time, spinel lithium titanium oxide containing anatase titanium dioxide, rutile titanium dioxide and Li ₂ TiO ₃ as impurities can be obtained. Small particles of Li ₄ Ti ₅ O ₁₂ can be prepared by high-energy ball milling of traditional microcrystalline spinels. The product was about 600 nm in size, so that the electrochemical performance was not significantly different from that of the unmilled initial material. T. Ohzuku et al. Obtained hydrogen tube spinel Li ₄ Ti ₅ O ₁₂ through ion-exchange with lithium using hydrogen titanium oxide nanotubes as precursors [ J. Electrochem. Soc . 1995 , 142, 1431; J. -R. Li et al . , Electrochem. Commum . 2005 , 7, 894]. These Li ₄ Ti ₅ O ₁₂ have a problem of having a relatively low lithium-insertion capacity at high charge rate.

Therefore, if a method for producing a uniform type of spinel lithium titanium oxide nanotubes having improved electrochemical properties by a simple method is developed, it can be usefully used as a hydrogen ion storage body as a lithium secondary battery. do.

The present invention is to solve the above-mentioned problems can be used as an electrode material and hydrogen storage material of a lithium secondary battery and provides a manufacturing method that can mass-produce uniform spinel Li ₄ Ti ₅ O ₁₂ nanotubes in a simple process For that purpose.

Method for producing a spinel lithium titanium oxide of the present invention for achieving the above object is (A) titanium t-butoxide (titanium n-butoxide), lithium hydroxide and cetyltrimethyl ammonium salt Putting CTAS) into water and mixing uniformly; (B) hydrothermally treating the mixture at a temperature of 60-120 ° C. to produce Li ₄ Ti ₅ O ₁₂ nanoparticles; (C) heat-treating the Li ₄ Ti ₅ O ₁₂ nanoparticles produced by hydrothermal treatment at 300 ~ 500 ℃; And (D) hydrothermally reacting the heat treated Li ₄ Ti ₅ O ₁₂ nanoparticles in an aqueous alkali solution.

Hereinafter, each step will be described in more detail.

(A) mixing of precursors

Titanium t-butoxide, a precursor of Li ₄ Ti ₅ O ₁₂ , lithium hydroxide and cetyltrimethyl ammonium salt are added to water and mixed homogeneously. This step is necessary for efficient hydrothermal reaction of the next step.

The cetyltrimethyl ammonium salt is preferably chloride (CTACl) or bromide (CTABr).

In the present invention, the molar ratio of the titanium t-butoxide: lithium hydroxide: cetyltrimethyl ammonium salt is preferably 1: 0.8-2: 1-2. If the molar ratio of lithium hydroxide is too small, titanium dioxide may be formed by the hydrolysis of only a relatively large amount of titanium t-butoxide, and may be contained as impurities. On the other hand, even more molar ratios do not affect the structure or purity of the resulting lithium titanium oxide, and since the lithium hydroxide remaining after the reaction is removed during the filtration and washing process, it is not meaningful to use more than the ratio. If the amount of cetyltrimethyl ammonium salt is less than the above molar ratio, the resulting Li ₄ Ti ₅ O ₁₂ plate-shaped nanoparticles may not be formed. If the amount of cetyltrimethyl ammonium salt is more than the above molar ratio, the effect on the structure of the nanoparticles is There is no economical aspect, but it is preferable that the above range.

The hydrothermal reaction between titanium t-butoxide and lithium hydroxide does not proceed effectively, and even if the amount is higher, the effect on the reaction is minimal.

In the present invention, the amount of water is preferably 0.35 to 1.4 times (w / w) of titanium t-butoxide. If the amount of water is too small, the hydrolysis reaction of titanium t-butoxide and lithium hydroxide may not occur sufficiently. If the amount of water is large, the morphology control is poor due to rapid hydrolysis reaction and the particle size Becomes large. The water may be reacted by adding to titanium t-butoxide, lithium hydroxide and cetyltrimethyl ammonium salt, but the cetyltrimethyl ammonium salt used is a reagent in an aqueous solution as in Example, and the amount of water contained in the reagent In the case of the said range, it does not need to use further.

(B) step of preparing Li ₄ Ti ₅ O ₁₂ nanoparticles

This step is to prepare Li ₄ Ti ₅ O ₁₂ nanoparticles by hydrothermal reaction of titanium t-butoxide and lithium hydroxide in the presence of cetyltrimethyl ammonium salt.

The hydrothermal reaction is preferably performed for 6 to 48 hours at 100 ~ 120 ℃.

The temperature of the hydrothermal reaction had the greatest influence on the structure of the synthesized Li ₄ Ti ₅ O ₁₂ nanoparticles and the reaction time did not significantly affect the structure of the nanoparticles. If the temperature is lower than 100 ° C, the structure of the preferred nanoparticles cannot be obtained. Although lithium titanium oxide nanoparticles are produced even when the temperature is higher than 120 ° C, the temperature is preferably 120 ° C or lower for efficiency of the process. If the reaction time is too short, the hydrolysis reaction does not proceed completely, and if the reaction time is longer when the hydrolysis is completed, it is meaningless to proceed with the reaction for more than 48 hours because it does not significantly affect the structure of the nanoparticles.

The crystal structure of Li ₄ Ti ₅ O ₁₂ prepared in this step was a 2-D plate-like structure as can be seen in FIG.

(C) heat treatment step

Heat treatment is performed to improve the crystallinity of the Li ₄ Ti ₅ O ₁₂ nanoparticles prepared in step (B). It is preferable to perform this heat processing process for 4-12 hours in 300-500 degreeC range. The higher the heat treatment temperature, the longer the firing time, the higher the crystallinity was. If the heat treatment temperature is too high, above 500 ° C., the 2-D plate structures may not only agglomerate with each other, but also may cause composition change or phase transformation due to oxidation.

(D) alkali hydrothermal step

The heat-treated Li ₄ Ti ₅ O ₁₂ nanoparticles are hydrothermally reacted in an aqueous alkaline solution to convert them into spinel-structured nanotubes through a rolling-up process.

It is preferable to use 5-10 M NaOH aqueous solution for the said alkaline aqueous solution. If the concentration of NaOH solution is too thin, the nanotube shape is not synthesized because it is not well rolled into nanotubes, and the concentration of 10M or more is practically difficult to apply, so there is no meaning.

In addition, the hydrothermal reaction is preferably performed for 12 to 48 hours at 100 ~ 150 ℃. When the alkali hydrothermal reaction is performed at 100 ° C. or lower, the shape or crystallinity of the resulting nanotubes is not good, and it is preferable to proceed at 150 ° C. or lower for efficiency of the process.

The spinel lithium titanium oxide nanotubes prepared according to the present invention were relatively uniform in size with an inner diameter of about 5 nm and an outer diameter of about 11 nm. Battery capacity close to 175 mAh / g, which is the theoretical battery capacity of Li ₄ Ti ₅ O ₁₂ , was shown. In addition, it was confirmed that it was useful as an electrode active material of a lithium secondary battery by exhibiting excellent cycle characteristics in the 25th battery charge / discharge cycle test. In addition, it showed that the room temperature hydrogen storage capacity of 0.7wt% high at room temperature also has excellent characteristics as a hydrogen storage material.

As described above, according to the present invention, Li ₄ Ti ₅ O ₁₂ nanotubes having a spinel structure having a good moving speed of lithium ions and good structural stability even after charging and discharging can be synthesized uniformly. The spinel-structured Li ₄ Ti ₅ O ₁₂ nanotubes produced by the method of the present invention are not only applicable to lithium ion batteries as electrode materials and large-capacity storage materials, but also environmentally friendly alternative energy storage materials, which are one of the most active research fields in recent years. As a result, the economic ripple effect is expected to be very large due to the real-time storage of hydrogen.

The present invention will be described in detail through the following examples. However, these examples are for illustrative purposes only and the present invention is not limited thereto.

Example

Example 1 Spinel Li ₄ Ti ₅ O ₁₂  Preparation of Nanotubes

1) 2-D plate structure Li ₄ Ti ₅ O ₁₂  Steps for preparing nanoparticles

Titanium n-butoxide (97%, Aldrich) 8.2g (0.00157mol) and cetyltrimethyl ammonium chloride (25wt% in water solution, Aldrich) 8.2g (0.0296mol) were mixed for 1 hour using a mechanical stirrer. After homogeneously mixing, 1.86 g of lithium hydroxide (99%, Aldrich) was added and then mixed for about 1 hour. The mixture was transferred to a 100 ° C. oven and hydrothermally reacted for 24 hours. The precipitate produced by the hydrothermal synthesis was filtered under reduced pressure, washed two or three times with distilled water and ethanol, and then dried in a dry oven at 40 ° C. for 12 hours.

Li ₄ Ti ₅ O ₁₂ prepared by the above method The nanoparticles were observed by transmission electron microscopy (JEOL 2100F), and the results are shown in FIG. 1. From FIG. 1, it can be seen that Li ₄ Ti ₅ O ₁₂ nanoparticles having a 2-D plate structure were synthesized.

2) heat treatment step

Li ₄ Ti ₅ O ₁₂ nanoparticles of the 2-D plate structure prepared in 1) was transferred to a furnace capable of high temperature heat treatment, and heated at a rate of 5 ° C./min, and heat treated at 500 ° C. for about 6 hours in air. It was.

3) alkali hydrothermal reaction step

 100 ml of 10 M NaOH solution was added to 2 g of the white precipitate, which was heat-treated in 2), in a PP bottle, followed by hydrothermal reaction at 120 ° C. for 24 hours. When the reaction was completed, the reaction product was filtered through a reduced pressure filter and washed two to three times with distilled water and ethanol and then dried in a dry oven at 40 ℃ for 12 hours.

2 and 3 shows the drying is complete Li ₄ Ti ₅ O ₁₂ Transmission Electron Microscopy (JEOL 2100F) photographs of the nanoparticles show that the Spitel structured nanotubes were well formed by the method of this example. As can be seen in Figures 2 and 3, the Li ₄ Ti ₅ O ₁₂ nanotubes according to the present invention is an open-ended tublar shape of the inner diameter of about 6nm, the outer diameter of about 11nm is the interlayer spacing of the nanotubes ~ 0.51 nm, fine fringes perpendicular to the nanotube direction were 0.28 nm.

X-ray diffraction (BRUKER D8 ADVANCE) of the nanotubes was performed and the results are shown in FIG. 4. FIG. 4 is an X-ray diffraction (BRUKER D8 ADVANCE) spectrum of a spinel structure of Li ₄ Ti ₅ O ₁₂ nanotubes prepared according to the preparation methods of Examples 1, 2 and 3. 4 and Li ₄ Ti ₅ O ₁₂ of the bulk structure (a = b = c = 8.378 Å, β = 90 °, JCPDS card No. Compared with the X-ray diffraction spectrum of 49-0207), the peaks are almost identical, and the synthesized spinel-structured nanotubes can be indexed with Li ₄ Ti ₅ O ₁₂ (a = b = c = 8.358 Å, β = 90 °). there was. In case of Li ₄ Ti ₅ O _12, the crystal structure is similar to that of LiTi ₂ O ₄ , which is the same spinel structure, but the position of the peak is slightly shifted to the right.

Example 2 Spinel Li ₄ Ti ₅ O ₁₂  Evaluation of Cell Characteristics of Nanotubes

The spinel Li ₄ Ti ₅ O ₁₂ nanotubes prepared in Example 1 were finely ground to have an average particle diameter of 5 μm, and acetylene black, N-methyl pyrrolidone (NMP) and PVDF (Polyvinylidine Difluoride) at 10% by weight of the nanotubes. ) Was mixed. The mixture was coated on an aluminum sheet, dried at 100 ° C. for 30 minutes, cooled to room temperature, compressed, and dried at 120 ° C. for 24 hours. Lithium metal was used as a cathode, a separator was used, and a button cell crimping machine (Crimping M / C, Rotec P01) using 1M LiPF6 in 1: 1 weight ratio of ethylene carbonate (EC) / diethyl carbonate (DEC) as an electrolyte. Cell was prepared. Battery characteristics such as cell capacity, charge / discharge rate, and charge / discharge repeatability (cyclability) were evaluated at room temperature using a charge-discharge analyzer (WonC, WBCS 5000). 7 is shown.

5 is a graph showing the result of discharging at 0.2C after charging with various currents of 0.1 ~ 2C to evaluate the positive electrode active material properties of spinel Li ₄ Ti ₅ O ₁₂ nanotubes. As can be seen in FIG. 5, it was confirmed that about 97% of the 0.2C charge capacity was maintained during 2C charging, so that the slow diffusion of lithium ions in the solid phase was compensated for by the increase in the surface area due to the nanotube structure.

FIG. 6 is a graph showing cell capacity and shows that the cell capacity after the first charge and discharge is reversible within 5% at 163mAh / g and 156mAh / g, respectively.

Figure 7 is a graph showing the change in cell capacity with repeated charge and discharge, despite the large surface area of the spinel Li ₄ Ti ₅ O ₁₂ nanotubes according to the present invention there was no decrease in capacity in 25 cycles experiment Shows.

Example 3 Spinel Li ₄ Ti ₅ O ₁₂  Surface Area Measurement of Nanotubes

Pressure adsorption / desorption with respect to the spinel Li ₄ Ti ₅ O ₁₂ nanotubes prepared in Example 1 was measured at -196 ℃ using a gas sorption analyzer (Micromeritics, ASAP 2020) and the results are shown in FIG. . Samples were first degassed at 473K and vacuumed at 10 ⁻³ torr or lower for 12 hours prior to measurement. The graph of FIG. 8 corresponds to type IV exhibiting some hysteresis according to IUPAC classification. The large increase in nitrogen adsorption above P / P ₀ = 0.8 is due to capillary condensation. The surface area of the spinel Li ₄ Ti ₅ O ₁₂ nanotubes according to this example was calculated by Brunauer-Emmett-Teller (BET) equation, and the result was 53.69 m ² / g and pore volumn was 0.29 cm ³ / g.

Example 4 Spinel Li ₄ Ti ₅ O ₁₂  Evaluation of Hydrogen Storage Characteristics of Nanotubes

RUBOTHERM system capable of adsorption isotherm experiments at high pressure (135 bar) and high temperature (525K) for spinel Li ₄ Ti ₅ O ₁₂ nanotubes prepared in Example 1 (consisting of balance, magnetic coupling and adsorption chamber for analysis Hydrogen storage was measured.

The sample for measuring the hydrogen storage was dried at 70 ° C. for 7 hours to remove foreign substances in the sample.

In order to calibrate the buoyancy effect on the volume of the sample, it was measured by blowing helium, an inert gas, into the sample.

Measurement of the adsorption amount of hydrogen is shown in Figure 9 by measuring the hydrogen adsorption amount according to the pressure change at room temperature. As can be seen in Figure 9 spinel Li ₄ Ti ₅ O ₁₂ nanotubes as the hydrogen pressure increases the amount of hydrogen adsorbed, about 0.7wt% of hydrogen at 100 bar is adsorbed hydrogen at room temperature than the general porous material Storage capacity was shown.

1 is a transmission electron microscope photograph of Li ₄ Ti ₅ O ₁₂ nanoparticles having a 2-D plate structure.

Figure 2 is a transmission electron micrograph of the spinel Li ₄ Ti ₅ O ₁₂ nanotubes prepared by one embodiment of the present invention.

Figure 3 is a high magnification transmission electron micrograph of the sample of Figure 2;

4 is an X-ray diffraction spectrum of the sample of FIG. 2.

5 is a graph showing the rate capability at room temperature of the sample of FIG.

6 is a graph showing the cell capacity of the sample of FIG.

7 is a graph showing the cell cyclability of the sample of FIG.

8 is a nitrogen adsorption / desorption curve of the sample of FIG.

Figure 9 is a graph showing the hydrogen storage capacity of the spinel Li ₄ Ti ₅ O ₁₂ nanotubes prepared by one embodiment of the present invention.

Claims (8)

(A) Titanium n-butoxide, lithium hydroxide, and cetyltrimethyl ammonium chloride or cetyltrimethyl ammonium salt (cetyltrimethyl ammonium salt, CTAS) in water and uniformly Mixing; (B) hydrothermally treating the mixture at a temperature of 60-120 ° C. to produce Li ₄ Ti ₅ O ₁₂ nanoparticles; (C) heat-treating the Li ₄ Ti ₅ O ₁₂ nanoparticles produced by hydrothermal treatment at 300 ~ 500 ℃; And (D) hydrothermally reacting the heat treated Li ₄ Ti ₅ O ₁₂ nanoparticles in an aqueous alkali solution; Spinel lithium titanium oxide manufacturing method comprising a. The method of claim 1, The molar ratio of the titanium t-butoxide: lithium hydroxide: cetyltrimethyl ammonium salt is 1: 0.8 ~ 2: 1 to 2, characterized in that the manufacturing method of spinel lithium titanium oxide. The method of claim 1, The hydrothermal reaction of step (B) is a method for producing spinel lithium titanium oxide, characterized in that for 6 to 48 hours at 100 ~ 120 ℃. The method of claim 1, The heat treatment of step (C) is a method for producing spinel lithium titanium oxide, characterized in that performed for 4 to 12 hours in the 300 ~ 500 ℃ range. The method of claim 1, The alkaline aqueous solution of step (D) is a method for producing spinel lithium titanium oxide, characterized in that 5 ~ 10M NaOH aqueous solution. The method of claim 1, The alkali hydrothermal reaction of step (D) is a method for producing spinel lithium titanium oxide, characterized in that for 12 to 48 hours at 100 ~ 150 ℃. delete A hydrogen storage material containing spinel lithium titanium oxide prepared by the method of any one of claims 1 to 6 as an active material.

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