KR101233700B1 - Method for Manufacturing Lithium Titanate Heterogeneous Nano Structures and Anode Active Materials Comprising the Same - Google Patents

Abstract

The present invention is a step of dispersing by adding a titanate nanowire and a lithium precursor to the solvent; Performing a hydrothermal reaction on the dispersed solution; Centrifuging and washing the finished solution to obtain a precipitate; And 4 steps of freeze drying and calcination of the precipitate; It relates to a method for producing a lithium titanate hetero nanostructure comprising a.
The negative electrode active material including the lithium titanate hetero nanostructures prepared by the above method is characterized by lithium titanate having an insertion / desorption reaction with lithium in terms of electrochemical properties. Has characteristics. In addition, it has a wider specific surface area than the conventional nanostructure consisting of only 0-dimensional nanoparticles or 1-dimensional nanowires, and thus has the advantage of implementing improved electrochemical properties through reaction with lithium as a negative electrode active material. .

Description

Method for manufacturing lithium titanate heterostructures and a negative electrode active material comprising the same {Method for Manufacturing Lithium Titanate Heterogeneous Nano Structures and Anode Active Materials Comprising the Same}

The present invention relates to a method for producing a 0-dimensional 1-dimensional lithium titanate hetero nanostructures and a negative electrode active material comprising the same.

High performance of lithium-ion secondary batteries is closely related to the development and improvement of physical properties of electrode active materials, which are key factors.In particular, in the case of lithium-ion secondary battery electrode active materials, innovative ideas and advanced nanotechnology are appropriate to avoid development of simple materials and process technologies. Fusion is necessary. Recently, the development of a secondary battery electrode active material has been attempted to implement a composite nanostructure electrode to maximize the performance of the developed countries. In the positive electrode material represented by the cobalt oxide layered structure, spinel structure, and olivine structure, researches such as composite substitution and nano carbon coating have been published to increase electrical conductivity or safety, and the negative electrode material can replace the existing carbon material. Research on high performance composite nanostructure electrodes has been attempted.

In particular, in the case of the negative electrode active material, the negative electrode active material based on the insertion / desorption reaction of lithium ions of carbon-based materials is still the core in the negative electrode material field of lithium secondary battery technology, and its use is made in products that are still commercialized. However, in the case of the carbon-based negative active material, it is known that the capacity commercialized with a small theoretical capacity (372 mAh / g) is basically smaller than this. Furthermore, due to the disadvantage that the irreversibility of the lithium secondary battery increases due to side reactions generated between the negative electrode active material and the electrolyte solution during the charging and discharging process, there is a limit to meeting the large capacity required in portable electronic devices or electric vehicles. . Therefore, in recent years, the research on the negative electrode active material to replace the carbon-based material is actively in progress, many research cases have been reported. Representatively CuO, which expresses its capacity through a reaction (alloying reaction) using Si, Ge, Sn, etc., which forms an alloy with lithium, or a conversion reaction between metal / metal oxides, rather than an existing insertion / desorption process, Attention has been paid to transition metal oxides such as CoO, Fe ₂ O ₃ , NiO, MnO _2, etc. [WJ Weydanz et al., J. Power Sources 237 (1999) 81; P. Poizot et al., Nature 407 (2000) 496].

However, in the case of a negative electrode active material that realizes a capacity through the reaction with lithium, it is possible to realize a high capacity electrochemical characteristic with a higher theoretical capacity than active materials having a reaction of conventional insertion / desorption, but is reversible at charging and discharging. Aggregation between particles, with hundreds of percent volume change during the reaction, causes the capacity to drastically decrease with the number of cycles, with the limitation of achieving high power [R. Yang et al., Electrochem. Solid-State Lett. 7 (2004) A496-A499].

Therefore, many studies have been made to replace the carbon-based active material, and many studies have been conducted on methods of preparing lithium titanate and examples of using them as electrode materials, and also recently using lithium titanate. Reports on the use of negative electrode active materials have also been published [S. Scharner et al., J. Electrochem. Soc. 146 (1999), 857; Japanese Patent Laid-Open No. 2001-243950; Japanese Patent Laid-Open No. 2001-240498; Republic of Korea Patent Application Publication No. 10-2008-0023831; Republic of Korea Patent Registration 10-0726027; Republic of Korea Patent Application Publication No. 10-2004-0053104; Republic of Korea Patent Publication 10-2008-0096023].

In the case of lithium titanate, the capacity can be realized through insertion / desorption reaction with lithium during charging and discharging like conventional carbon-based active materials. As a result, the lithium titanate has almost no change in volume and also changes in structure as lithium enters and exits. As a material that does not occur, it shows the advantage of having high cycle stability. However, this also has a limitation in the electrochemical characteristics of the capacity and output due to the low electrical conductivity of the active material, and needs to be solved.

Recently, research examples of preparing lithium titanate in various nanostructures and using it as a negative electrode active material of a lithium ion secondary battery have been developed [Y. Li et al., Mater. Lett. 63 (2009), 304; Y.F. Tang et al., Electrochem. Comm. 10 (2008), 1513; J. Huang et al., Elecrochem. Solid-state Lett. 11 (2008), A116.

In particular, lithium titanate having such nanostructures exhibits characteristics that were not seen in the bulk state, as well as nanoparticles (0 dimensions) as well as one-dimensional nanostructures such as nanowires, nanotubes, and nanorods. However, the characteristics may vary depending on the shape of various nanostructures. In addition, due to the large specific surface area, which is one of the greatest features of the nanostructure, the reaction site capable of reacting with lithium is increased, and the diffusion active distance of lithium ions is shortened. Looks at its characteristics. As described above, many researches for synthesizing nanostructures of lithium titanate have been actively conducted because they can be applied in various fields based on superior properties in bulk.

As described above, the conventional manufacturing method for producing the above-mentioned lithium titanate is largely divided into two phases, a liquid phase reaction method and a solid phase reaction method.

Among known production methods, representative liquid phase reaction methods are sol-gel method [Y. H. Rho et al., J. Electrochem. Soc. 150 (2003), 107], a mixed solution containing titanium and a lithium precursor is prepared, and a gel of the mixed solution is formed through a chelating agent, followed by a series of processes of heat treating and pulverizing the prepared gel [ WO 2003/012901, US Patent 2004/0217335]. However, in this case, while lithium titanate having a relatively high crystallinity can be produced, the process is complicated, and wastewater treatment is difficult, resulting in environmental problems.

In addition, the ball-milling method (A. Guerfi et al., J. Power Sources 126 (2004), 163; In the case of K. Zaghib et al., J. of Power souce 81-82 (1999), 300, lithium titanate was prepared by simply mixing a precursor of titanium and lithium, followed by heat treatment and grinding after mixing by ball milling. Compared to the liquid phase reaction, the manufacturing process can be simplified, but by-products other than the phase having a lithium titanate crystal structure of a desired composition are produced, and lithium is volatilized, making it difficult to control the composition ratio of titanium and lithium, It is difficult to produce single phase lithium titanate efficiently.

In addition, these methods are not only difficult to control the elemental composition of lithium, titanium and oxygen, it is difficult to control the shape of the prepared lithium titanate nanostructures and to produce lithium titanate of uniform size, and also various types of lithium titanate It is difficult to obtain nanostructures, and there is a disadvantage in that heat treatment is performed for a long time at a temperature of 800 ° C. or higher.

Therefore, the case of preparing lithium titanate through the above-described manufacturing method shows that the method of synthesizing lithium titanate having a uniform nanostructure having a large specific surface area with a simplified synthesis process and low temperature synthesis is provided. Required.

It is an object of the present invention to provide a method for producing a lithium titanate heterostructure having improved electrochemical characteristics compared to conventional nanostructures.

The present invention relates to a method for producing a 0-dimensional 1-dimensional lithium titanate heterostructure. In the present invention, one-dimensional is a concept including all forms of nanowires, nanotubes, nanorods, and the like, and zero-dimensional is a concept including nanoparticles in the form of dots.

Specifically, the lithium titanate heterostructures are prepared by the following method.

Adding a titanate nanowire and a lithium precursor to a solvent to disperse it;

Performing a hydrothermal reaction on the dispersed solution;

Centrifuging and washing the finished solution to obtain a precipitate; And

4 steps of freeze drying and calcination of the precipitate;

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The present invention also relates to a secondary battery employing a negative electrode active material for a secondary battery comprising a lithium titanate heterogeneous nanostructure produced by the above method, and a negative electrode containing the negative electrode active material.

The method for producing a lithium titanate heterostructure according to the present invention can be easily obtained, and the yield can be increased by increasing the capacity of the reactor, thereby facilitating mass production and simplifying at low temperature without complicated intermediate processes. It is economical and time-saving because the process is simple due to the progress of the hydrothermal reaction. Above all, since it is easy to control the parameters of the reaction, the greatest advantage is that it is possible to obtain a unique shape of lithium titanate heterostructures by controlling the reaction temperature and time of hydrothermal synthesis, the use of various mixed solvents.

In addition, the negative electrode active material including the lithium titanate heterostructures prepared by the above method has the characteristics of lithium titanate having an insertion / desorption reaction with lithium in terms of electrochemical properties, and thus high power / It has the characteristics of long life. In addition, it has a wider specific surface area than the conventional nanostructure consisting of only 0-dimensional nanoparticles or 1-dimensional nanowires, and thus has the advantage of implementing improved electrochemical properties through reaction with lithium as a negative electrode active material. .

Therefore, the lithium titanate heterostructures of various shapes through the simple hydrothermal synthesis reaction presented in the present invention are based on the advantages of simple synthesis process and economical and mass production, such as lithium secondary battery, electric double layer super capacitor, pseudo super capacitor, etc. Various applications are possible across the industry.

1 is a field emission scanning electron microscope (FESEM) image of a titanate nanowire.
2 is a field emission scanning electron microscope image of the lithium titanate heterostructures prepared in Examples 1 to 3 [(a) to (c)].
3 is an X-ray diffraction pattern analysis of the lithium titanate heterostructures prepared in Examples 1-11.
4 is a field emission scanning electron microscope of lithium titanate heterostructures prepared in Examples 12 to 15 [(a) to (d)] and Example 3 (e).
5 is a Transmission Electron Microscopy (TEM) image of the lithium titanate heterostructures prepared in Examples 14 (a), 15 (b), and 3 (c).
6 is an X-ray diffraction pattern analysis result of the nanostructures prepared in Example 3 and Examples 16 to 25.
7 is a field emission scanning electron microscope image of the nanostructures prepared in Example 16 (a), Example 17 (b), Example 18 (c), Example 3 (d), and Example 23 (e). .
8 is a transmission electron microscope image of the lithium titanate and lithium titanate heterostructures prepared in Example 17 (a), Example 3 (b), and Example 23 (c).
9 is a high-resolution transmission electron microscope image of the one-dimensional nanowires and the 0-dimensional nanoparticles attached to the surface of the lithium titanate heterostructures prepared in Example 3.
10 is a field emission scanning electron microscope image of the lithium titanate heterostructure / carbon nanotube prepared in Example 26.
FIG. 11 is a current change curve of voltages of lithium titanate hetero-nanostructure negative active materials prepared in Examples 2, 3, 5, 21, 23, 24, and 26 [(a) to (g)].
12 is a cycle test result of the nanostructures prepared in Examples 2, 3, 5, 21, 23, 24, 26.
13 is a cycle test result of the nanostructures prepared in Examples 2, 3, 5, 21, 23, 24, 26.

Hereinafter, the present invention will be described in detail.

The present invention is a step of dispersing by adding a titanate nanowire and a lithium precursor to the solvent;

Performing a hydrothermal reaction on the dispersed solution;

Centrifuging and washing the finished solution to obtain a precipitate; And

4 steps of freeze drying and calcination of the precipitate;

It relates to a method for producing a lithium titanate hetero nanostructure comprising a.

The method for producing a lithium titanate heterostructure using the hydrothermal synthesis reaction is simple, the hydrothermal synthesis is possible at a relatively low temperature, there is an advantage that can be mass-produced by increasing the capacity of the reactor. In addition, there is an advantage in that the shape of the lithium titanate can be modulated by controlling the temperature and time of the hydrothermal synthesis reaction together with easy control of the dielectric constant through controlling the ratio of the mixed solvent.

The titanate nanowires in step 1 were dispersed in sodium hydroxide (NaOH) solution of titanium oxide powder in anatase, followed by a hydrothermal synthesis reaction, and sodium titanate (Na ₂ Ti ₃ O ₇ ) obtained through washing and drying. The titanate precipitate obtained by dispersing the nanowires in a hydrochloric acid solution can be prepared by washing and drying.

In the hydrothermal reaction of the titanate nanowires, it is preferable to maintain the reaction time for 1 to 48 hours at 150 to 200 ° C. If the reaction temperature is low or the reaction time is not sufficient, the shape of the last titanate formed is This is because the shape of the one-dimensional nanowire is not shown. After the reaction, precipitates are obtained by centrifugation, washing with ethanol and deionized water and vacuum drying at 30 to 100 ° C.

While dispersing the titanate nanowires in a hydrochloric acid solution, a cation exchange reaction between sodium ions (Na ⁺ ) and hydrogen ions (H ⁺ ) in solution occurs in sodium titanate, which results in a lower power of hydrogen cations than sodium cations. It is due to the greater.

The solvent may be deionized water, C ₁ to C ₆ alcohol or a mixture thereof. Various types of lithium titanate nanostructures may be manufactured by various types of solution types and mixing ratios. This is due to the difference in the dielectric constant of each solvent. For solvents with low dielectric constants, it is easier to reach higher saturation, thereby increasing the rate of nucleation of the synthetic material in solution. The size of the nucleus produced is reduced. The most preferable solution is a mixture of deionized water and ethanol, and most preferably 60 to 80% by volume of ethanol and 20 to 40% by volume of deionized water.

Carbon nanotubes may be further added to the solvent to finally prepare a lithium titanate / carbon nanotube composite. The carbon nanotubes may be added 1 to 50% by weight relative to the solvent, the prepared lithium titanate / carbon nanotube composite is excellent in electrochemical properties.

The lithium precursor may be lithium chloride hydrate (LiCl.xH ₂ O), lithium sulfide hydrate (Li ₂ SO ₄ .xH ₂ O), lithium acetate hydrate (Ch ₃ COOLi.xH ₂ O), lithium nitrate (LiNO ₃ ), There may be lithium carbonate (Li ₂ CO ₃ ) or lithium hydroxide hydrate (LiOH.xH ₂ O), but preferably lithium hydroxide monohydrate (LiOH.H ₂ O).

The lithium precursor is preferably added to adjust the amount so that the lithium (Li) in the lithium precursor and titanium (Ti) in the titanate nanowire is 1: molar ratio of 0.5 to 5.

The hydrothermal synthesis in the second step is preferably reacted for 1 minute to 48 hours at a temperature of 90 ~ 250 ℃. When satisfying the above conditions, it is possible to produce a lithium titanate heterostructure having more excellent electrochemical properties.

The third step is specifically to separate the supernatant and the precipitate by centrifugation of the reaction solution, the supernatant is removed and the precipitate obtained by performing the washing process using ethanol and deionized water. At this time, the precipitate is formed in the crystal structure of lithium titanate by hydrothermal synthesis reaction. This is followed by a 48 hour freeze drying process.

In the step 4, the calcination process may obtain a final single-phase lithium titanate heterostructure having high crystallinity over 0.5 to 4 hours in an air atmosphere of 300 to 1000 ° C. In addition, the advanced calcination process is maintained at 0.5 to 4 hours after reaching 300 to 1000 ℃ at an elevated temperature rate of 1 to 10 ℃ per minute under an air atmosphere, at this time does not satisfy the conditions of gas atmosphere, temperature, time If not, it is preferable to obtain the nanostructured powder having low crystallinity or to obtain a lithium titanate powder having the desired single phase crystal structure.

Meanwhile, the lithium titanate heterostructures prepared in the above manner may be used for electrochemical devices, more specifically, lithium ion secondary batteries, electric double layer supercapacitors, and the like.

The present invention relates to a negative electrode active material comprising a lithium titanate hetero nanostructure prepared in the above manner.

The present invention also relates to a lithium secondary battery including the negative electrode active material.

A method of manufacturing a lithium secondary battery including the negative electrode active material may be by a general method of manufacturing a lithium secondary battery, and a detailed description thereof will be omitted in the present invention.

Hereinafter, the present invention will be described in more detail with reference to examples, but the following examples are merely to illustrate the present invention, but it should be understood that the present invention is not limited thereto.

Manufacturing example  : Titanate Nano-ray  Produce

The titanate nanowires were dispersed in 200 ml of 10 M sodium hydroxide (NaOH) solution in anatase titanium oxide powder (Sigma-Aldrich), which was subjected to hydrothermal synthesis at 180 ° C. for 24 hours, followed by washing and Sodium titanate (Na ₂ Ti ₃ O ₇ ) obtained through drying was prepared by washing and drying the titanate precipitate obtained by dispersing in 0.1 M hydrochloric acid solution and waiting at room temperature for 24 hours.

The shape of the prepared titanate nanowires was confirmed through a field emission scanning electron microscope (FESEM) photograph and the results are shown in FIG. 1. The prepared titanate nanostructures have a one-dimensional nanowire shape and can be seen to exhibit a smooth surface state.

Example  1 to 11: Lithium titanium composition ratio

In consideration of the titanate nanowires and the lithium hydroxide monohydrate powder prepared in the preparation example to be the final production of lithium titanate, as shown in Table 1, the weight ratio of the lithium and titanium in consideration of the weight ratio, ethanol and The volume ratio of deionized water was disperse | distributed on the solvent mixed with the ratio of the following Table 1, and sufficient stirring was performed for 1-2 hours at normal temperature. Thereafter, the hydrothermal reaction was performed for 24 hours at a temperature of 180 ° C., followed by centrifugation and washing with ethanol and deionized water. Finally 48 hours of freeze drying were performed. Thereafter, the obtained composite was subjected to a calcination process at 500 ° C. or 800 ° C. for 2 hours under an air atmosphere, respectively, to obtain final nanopowders. Table 1 shows the specific conditions according to each example.

menstruum Hydrothermal synthesis Composition ratio calcination ethanol
(volume%) Distilled water
(volume%) Temperature
(℃) time
(h) (Li: Ti) Temperature (℃) time
(h) Example 1 60 40 180 24 1: 0.8 500 2 Example 2 1: 1.0 Example 3 1: 1.05 Example 4 1: 1.1 Example 5 1: 1.2 Example 6 1: 0.8 800 Example 7 1: 1.0 Example 8 1: 1.1 Example 9 1: 1.2 Example 10 1: 1.6 Example 11 1: 2.4

The shape of the nanostructures prepared according to Examples 1 to 3 was confirmed through a field emission scanning electron microscope and the results are shown in FIG. 2. In FIG. 2, (a) shows Example 1, (b) shows Example 2, and (c) shows Example 3. FIG. As shown in Figure 2, it was confirmed that the lithium titanate nanostructures of different shapes according to the composition ratio of lithium and titanium.

The results of XRD diffraction patterns of the nanostructures prepared in Examples 1 to 11 are shown in FIG. 3. As shown in FIG. 3, the crystal structures of the nanostructures prepared according to Examples 1 to 11 represent single phase lithium titanate (Li ₄ Ti ₅ O ₁₂ ) according to the above conditions, and titanium oxide (TiO ₂ , anatase, rutile phase) and another form of the lithium titanate (LiTiO ₂ ) crystal structure with the secondary phase included together.

Example  12 to 15: hydrothermal synthesis temperature and time

After weighing the titanate nanowires and the lithium hydroxide monohydrate powder prepared in the preparation example in consideration of the lithium titanate to be finally prepared, the ratio of lithium and titanium to be the composition ratio of 1: 1.05 The volume ratio of the ionized water was dispersed on the solvent mixed in the ratio of 60:40, and sufficient stirring was performed for 1 to 2 hours at normal temperature. Thereafter, the hydrothermal synthesis reaction was performed according to the temperature and time shown in Table 2 below, followed by centrifugation and washing with ethanol and deionized water. Finally 48 hours of freeze drying were performed. Thereafter, the obtained composites were subjected to a calcination process at 500 ° C. for 2 hours under an air atmosphere to obtain final nanopowders. Table 2 shows the specific conditions according to each example.

menstruum Hydrothermal synthesis Composition ratio calcination ethanol
(volume%) Distilled water
(volume%) Temperature
(℃) time
(h) (Li: Ti) Temperature (℃) time
(h) Example 3 60 40 180 24 1: 1.05 500 2 Example 12 90 8 Example 13 180 1 min Example 14 One Example 15 6

The shapes of the lithium titanate heterostructures prepared in Examples 12 to 15 [(a) to (d)] and Example 3 (e) were confirmed through a field emission scanning electron microscope, and the results are shown in FIG. 4. It was. As shown in FIG. 4, it was confirmed that lithium titanate nanostructures having different shapes were manufactured according to the temperature and time of hydrothermal synthesis.

In addition, Figure 5 shows a transmission electron microscope image of the lithium titanate heterostructures prepared in Example 14 (a), 15 (b), 3 (c). As shown in Figure 5, it can be seen that the nanoparticles are produced in various sizes, distribution.

Example  16-25: solvent mixing ratio and calcination temperature

After weighing the titanate nanowires and the lithium hydroxide monohydrate powder prepared in the preparation example in consideration of the lithium titanate to be finally prepared, the ratio of lithium and titanium to be the composition ratio of 1: 1.05 The volume ratio of the ionized water was dispersed on the solvent mixed in the ratio shown in Table 3 below, and sufficient stirring was performed at room temperature for 1 to 2 hours. Thereafter, the hydrothermal synthesis reaction was performed at 180 ° C. for 24 hours, followed by centrifugation and washing with ethanol and deionized water. Finally 48 hours of freeze drying were performed. Thereafter, the obtained composite was subjected to a calcination process for 2 hours at the temperature shown in Table 3 under an air atmosphere to obtain a final nanopowder. Table 3 shows the specific conditions according to each example.

menstruum Hydrothermal synthesis Composition ratio calcination ethanol
(volume%) Distilled water
(volume%) Temperature
(℃) time
(h) (Li: Ti) Temperature (℃) time
(h) Example 3 60 40 180 24 1: 1.05 500 2 Example 16 0 100 500 Example 17 20 80 500 Example 18 40 60 500 Example 19 800 Example 20 60 40 300 Example 21 700 Example 22 800 Example 23 80 20 500 Example 24 700 Example 25 800

XRD diffraction pattern analysis of the nanostructures finally obtained through the Example according to Table 3 is shown in FIG. As shown in FIG. 6, the lithium titanate may be manufactured by changing the dielectric constant of the solvent according to the change of the proportion of the mixed solvent, and according to some embodiments, a second phase other than the lithium titanate occurs.

Field emission scanning electron microscope images of the nanostructures prepared according to Example 16 (a), Example 17 (b), Example 18 (c), Example 3 (d), and Example 23 (e) are shown. Shown in 7. In addition, transmission electron microscope images of the lithium titanate and lithium titanate heterostructures prepared in Example 17 (a), Example 3 (b), and Example 23 (c) are shown in FIG. 8. As shown in FIG. 7 and FIG. 8, it can be confirmed that lithium titanate having various shapes can be manufactured by changing the dielectric constant according to the ratio of the mixed solvent. This is due to the difference in dielectric constant of the solvent (ε deionized water = 80, ε ethanol = 25).

In addition, in the lithium titanate heterostructures prepared in Example 3, the one-dimensional nanowires and the 0-dimensional nanoparticles attached to the surface thereof were more closely observed using a high-resolution transmission electron microscope, and the results are shown in FIG. 9. . As can be seen from FIG. 9, it can be seen that the values of the interplanar distances of the lithium titanate are known to be the same in both the one-dimensional nanowires of the heterogeneous nanostructure and the portion of the 0-dimensional nanoparticles attached to the surface thereof. Lithium titanate hetero nanostructures having been prepared.

Example  26

It was prepared in the same manner as in Example 21, except that 20 wt% of the carbon nanotube (CM-100, Hanwha Nanotech) mixed solvent was added to the mixed solvent in which 60% by volume of ethanol and 40% by volume of distilled water were mixed.

menstruum Hydrothermal synthesis Composition ratio calcination ethanol
(volume%) Distilled water
(volume%) CNT addition amount (% by weight) Temperature
(℃) time
(h) (Li: Ti) Temperature (℃) time
(h) Example 21 60 40 - 180 24 1: 1.05 700 2 Example 26 60 40 20 180 24 1: 1.05 700 2

The field emission scanning electron microscope image of the lithium titanate heterostructures / carbon nanotubes prepared in Example 26 is shown in FIG. 10. As shown in Figure 10, by adding and reacting together carbon nanotubes in the hydrothermal synthesis reaction used to prepare the lithium titanate heterostructures of the present invention, the lithium titanate heterostructures and carbon nanotubes form a complex You can see how it is achieved.

Experimental Example

In order to compare and evaluate the lithium titanate hetero nanostructure negative electrode active material prepared in Examples 1 to 26 as a negative electrode active material for secondary batteries, the capacity of the half battery was measured.

Experimental Example  1: electrode manufacturing

1 mg of the lithium titanate hetero-nanostructure negative electrode active material prepared in Examples 1 to 26 was weighed such that the mass ratio was 60: 20: 20 with graphite (MMM Cabon) as a conductive agent and Kynar 2801 (PVdF-HFP) as a binder. Then, it was dissolved in N-methyl-pitolidon (NMP), an inert organic solvent, to prepare a slurry. Thereafter, the slurry was applied to a copper foil as a current collector, dried in a vacuum oven at 100 ° C. for 4 hours to volatilize an organic solvent, and then pressed into a circular shape having a diameter of 1 cm.

Experimental Example  2: Fabrication and measurement of half cell for evaluation of electrochemical properties

In order to find out the electrochemical characteristics of the lithium titanate hetero-nanostructure negative active material prepared in Examples 1 to 26, a lithium metal as a negative electrode and an electrode prepared in Experimental Example 1 as a positive electrode, an electrolyte and a separator between the two (Celgard 2400) was added and a half cell of Swagelok type was constructed. The electrolyte used was a material in which LiPF ₆ was dissolved in a solution in which a volume ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) was 1: 1. All procedures of the half cell preparation presented above were carried out in a glove box filled with argon, an inert gas.

The manufactured half-slave type half-cell has a constant-static mode while varying the voltage at 0.1 mV / sec between 1.0 and 2.5 V using a charge / discharge cycler (WBCS 3000, WonA Tech., Korea). The galvanostatic mode was used to measure the current density and current density. At this time, the current density was converted from the theoretical capacity of lithium titanate, and 500 cycle charge / discharge tests were performed at 1C current density. In addition, while performing the charge and discharge cycles of 10 times in each of the current density of 1C, 5C, 10C, 20C different range, the evaluation of the output characteristics of the active material according to the current density.

11 shows the current change curves according to the voltage change of the lithium titanate hetero-nanostructure negative electrode active material prepared in Examples 2, 3, 5, 21, 23, 24, and 26 [(a) to (g)].

In addition, FIG. 12 and FIG. 13 show cycle test results according to the measurement of the constant current method of the nanostructures prepared according to Examples 2, 3, 5, 21, 23, 24, and 26.

Table 5 and Table 6 show 500 times of charging and charging at a current density of 1C in the secondary battery characteristics evaluation of the lithium titanate heterostructured nanostructure negative electrode active material prepared according to Examples 2, 3, 5, 21, 23, 24, and 26. The discharge capacity when 10 charge and discharge cycle tests were performed while changing the discharge capacity and current density when performing a discharge cycle test to 1C, 5C, 10C, and 20C is shown.

Discharge Capacity (mAh / g) Current density: 1C cycle 10 50 100 200 300 400 500 Example 2 153 135 125 116 - - - Example 3 143 125 116 109 105 102 99 Example 5 130 119 115 108 - - - Example 21 148 142 134 132 130 127 125 Example 23 151 137 130 122 119 117 116 Example 24 144 138 133 129 127 124 120 Example 26 142 - - - - - -

Discharge Capacity (mAh / g) 10 cycles 1 C 5 C 10 C 20 C Example 2 153 125 116 98 Example 3 145 126 119 108 Example 5 122 107 101 89 Example 21 151 139 132 115 Example 23 144 127 114 92 Example 24 142 129 123 109 Example 26 157 144 127 81

Table 5 and Table 6 are more excellent electrochemical properties than the nano-powders of the lithium titanate heterostructures prepared by the synthesis method of Example 21 of the present invention compared to the nano-powders prepared by the synthesis method of another embodiment It shows the characteristics of capacitance and long life, and also shows that it is possible to realize high output characteristics in the measured capacitance characteristics while changing the current density. In particular, the lithium titanate heterostructures prepared according to Example 21 exhibited a high specific surface area of 70 m ² / g. From this, the negative electrode active material of the lithium titanate heterogeneous nanostructure prepared from the method of the present invention has many sites capable of reacting with lithium due to its high specific surface area, and thus has a high capacity characteristic, as well as lithium insertion / desorption reaction with lithium. Since there is almost no volume change during the reaction, it shows the characteristics of long life and high power, and it can be seen that high capacity can be maintained even at high current density.

Claims (13)

Adding a titanate nanowire and a lithium precursor to a solvent to disperse it;
Performing a hydrothermal reaction on the dispersed solution;
Centrifuging and washing the finished solution to obtain a precipitate; And
4 steps of freeze drying and calcination of the precipitate;
Method for producing a lithium titanate heterostructures comprising a.
According to claim 1, wherein the titanate nanowires disperse anatase titanium oxide powder in a sodium hydroxide (NaOH) solution to undergo a hydrothermal synthesis reaction, sodium titanate obtained by washing and drying (Na ₂ Ti ₃ O ₇ ) A method for producing a lithium titanate heterogeneous nanostructure, characterized in that obtained by dispersing the nanowires in a hydrochloric acid solution.
The method of claim 2, wherein the hydrothermal synthesis of the titanate nanowires is performed at 150 to 200 ° C. for 1 to 48 hours.
The method of claim 1, wherein the solvent is deionized water, C ₁ to C ₆ alcohol, or a mixture thereof.
The method of claim 4, wherein the solvent is a mixed solution of deionized water and ethanol.
The method of claim 5, wherein the solvent is a mixed solution of 60 to 80% by volume of ethanol and 20 to 40% by volume of deionized water.
The method of claim 1, wherein the carbon nanotubes are added in an amount of about 1 wt% to about 50 wt% with respect to the solvent.
The method of claim 1, wherein the lithium precursor, lithium chloride hydrate (LiCl · xH ₂ O), sulfide, lithium monohydrate _{(Li 2 SO 4 · xH 2} O), lithium acetate monohydrate _{(Ch 3 COOLi · xH 2 O} ), lithium nitrate ( LiNO ₃ ), lithium carbonate (Li ₂ CO ₃ ) or lithium hydroxide hydrate (LiOH.xH ₂ 0) The method for producing a lithium titanate hetero-nanostructures characterized in that.
The lithium titanate heterostructure of claim 1, wherein the lithium precursor is added so that the lithium (Li) in the lithium precursor and the titanium (Ti) in the titanate nanowire are in a molar ratio of 1: 0.5 to 5. Manufacturing method.
The method of claim 1, wherein the hydrothermal synthesis is performed for 1 minute to 48 hours at a temperature of 90 ~ 250 ℃.
The method of claim 1, wherein the calcination is performed over an air atmosphere of 300 to 1000 ° C over 0.5 to 4 hours.
An anode active material comprising a lithium titanate hetero nanostructure prepared by the method of any one of claims 1 to 11.
A lithium ion secondary battery comprising the negative electrode active material of claim 12.

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