KR101088268B1 - Lithium titanate with nanotube - Google Patents

Abstract

The present invention provides a lithium-titanium oxide nano-tube form, and also, by the reaction of the TiO ₂ powder in a first step of providing a TiO ₂ powder having a metastable state, LiOH aqueous solution containing the Li component by ion exchange A second step of forming a layered titanate, and a third step of heat-treating the titanate to convert the layered titanate containing the Li component into a nanotube structure: and an agent for drying the resultant It provides a method for producing lithium titanium oxide in the form of nanostructures comprising four steps.

Nano structure

Description

Lithium titanium oxide in the form of nanotubes {LITHIUM TITANATE WITH NANOTUBE}

The present invention relates to lithium titanium oxide having a nano structured form.

Recently, with the development of portable devices such as mobile phones, notebook computers, camcorders, and the like, demand for small secondary batteries such as Ni-MH (Ni-MH) secondary batteries and lithium secondary batteries is increasing. In particular, lithium using lithium and a nonaqueous solvent electrolyte has been actively developed due to the high possibility of realizing a battery of small size, light weight and high energy density. In general, a transition metal oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ is used as a cathode material of a lithium secondary battery, and lithium metal or carbon is used as an anode material. This is used, and a lithium secondary battery is comprised using the organic solvent which contains lithium ion as electrolyte between two electrodes. However, a lithium secondary battery using a metal lithium as a negative electrode tends to generate a dendrite crystal when charging and discharging is repeated, resulting in a high risk of short circuit. Lithium secondary batteries that use a nonaqueous solvent containing lithium ions as an electrolyte have been put to practical use. However, since the carbon-based negative electrode material has a large irreversible capacity, the initial charging and discharging efficiency is low, and the capacity is reduced.

On the other hand, there is also an attempt to use lithium titanate as a negative electrode material. Lithium titanium oxide has a voltage of 1.5V on the basis of lithium metal and has a long lifespan. In addition, it is a material that has been successfully used as an active material in a lithium ion battery for watches, and can be disregarded in expansion and contraction during charge-discharge, and thus, it is an electrode material that is noticed when the battery is enlarged. This material has been used conventionally as an anode material and can be utilized as a cathode material.

However, despite the fact that such a negative electrode containing lithium titanate has a relatively good rate performance, there is a need to improve the rate characteristic, which is superior to the present in applications requiring high power. There is. Rate performance is an indicator of the ability to discharge high current at high speed, and C-rate is defined as the current flowing when the battery capacity is discharged in one hour, and Rated capacity is C / rate. The discharge capacity when discharged by C-rate is expressed in% when the discharge capacity at 5% (current rate when exhausting the self-capacitance after discharge for 5 hours) is 100%. In general, in case of discharging with high C-rate, 100% of capacity cannot be discharged, and the higher the rated capacity, the better the rate characteristic. This has an important effect on the charging and discharging speed of the battery, and is evaluated as an important performance for applications in applications requiring large power, such as a power tool and a hybrid electric vehicle.

In the present invention, when the lithium titanium oxide is prepared in the form of nanostructures and used as an electrode material of the secondary battery, it was found that the rate characteristics of the battery can be improved to produce a high output secondary battery.

Accordingly, an object of the present invention is to provide a lithium titanium oxide having a nanostructured form and a method of manufacturing the same, and an electrode including the same and a secondary battery having the electrode.

The present invention provides a lithium titanium oxide having a nano-structure form.

In addition,

A first step of preparing a metastable TiO ₂ powder,

Reacting the TiO ₂ powder in a LiOH aqueous solution to form a layered titanate containing the Li component by ion exchange;

A third step of heat treating the titanate to convert the layered titanate containing the Li component into a nanotube structure; and

It provides a method for producing lithium titanium oxide in the form of nanostructures comprising a fourth step of drying the resultant.

The present invention also provides an electrode including the lithium titanium oxide of the nanostructure form as an electrode active material and a secondary battery comprising the electrode.

Hereinafter, the present invention will be described in detail.

According to the present invention, a lithium titanium oxide used as an electrode of a secondary battery, in particular, a negative electrode active material may be manufactured in a nanostructure to increase a specific surface area of an electrode, thereby speeding up diffusion of lithium ions and improving a rate characteristic of the battery.

When the active material is in the nanostructured form, the diffusion distance of lithium is shortened in the solid, thereby facilitating the diffusion of lithium and reducing the resistance, thereby increasing the rate characteristic of the battery.

In addition, the present invention uses a lithium titanium oxide as a negative electrode active material, such that a large irreversible capacity that can occur when using a carbon-based material (for example, carbon nanotube) as a negative electrode active material is large, such as a decrease in capacity. Problems inherent in carbon materials can also be solved.

Nanomaterials exhibit unusual mechanical and physical properties that are not expressed in ordinary powder materials as the particles become extremely fine. That is, in the case of solid crystalline, the chemical and physical properties have inherent properties only of the crystal. For example, melting point, boiling point, hardness, strength, and optical properties are inherent in the material, and the physical and chemical properties of the crystal are dependent on the crystalline component and crystal structure regardless of the crystalline form or size. . However, when the size of the material is nanoscale, the crystal size acts as a variable for the material's properties. As the nanoparticles are smaller in size, bulk properties decrease and surface properties rapidly increase, so the basic properties of materials, such as strength, magnetic and electrical properties, water absorption, catalytic performance, adsorption capacity, etc. This innovatively increasing nature is expected to lead to the application of nanomaterials in a variety of industries, including materials, machinery, electrical and electronics, as well as catalysts, medicine and biotechnology.

Among them, nanotubes have been widely studied in various technical fields because they have advantageous properties such as mechanical strength and material storage property due to the morphological properties of the nanomaterials as well as the surface properties of the nanomaterials.

In particular, titanate nanotubes have been of great interest in recent years due to photovoltaic cells, photocatalysts, semiconductors, catalyst supports and gas sensing, and hydrogen storage characteristics of titanate nanomaterials.

In an embodiment of the present invention, the lithium titanium oxide of the nanostructure may be lithium inserted into the crystal lattice of the titanium-containing crystalline oxide of the nanostructure.

Lithium titanium oxide in the present invention is a composition formula Li _x Ti _y O ₄ (0.5 ≦ x ≦ 3, 1 ≦ y ≦ 2.5). As a non-limiting example is _{Li 4 / 3Ti 5 / 3O 4} , LiTi 2 O 4, Li 4/5 Li 8/7 Ti1 2 having a Ti _11/5 O ₄ or person seudel light (ramsdellite) structure having a spinel structure _{/ 7} O _4, etc., and preferably may be a lithium-titanium oxide having _{Li 4/3 Ti 5/3} O 4 composition.

Since the ion radii of lithium and titanium in the lithium titanium oxide crystals are very close to each other, a slight difference in the synthesis method causes mutual substitution of lithium and titanium, resulting in a difference in peak position and intensity when X-ray diffraction analysis is performed. Even though they have stoichiometrically different compositions, they often have substantially the same crystal formation and typical peak positions. However, the ease of manufacturing and chemical stability, and it is the most advantageous in terms of charge-discharge capacity, the composition of the _{Li 4/3 Ti 5/3} O 4 as an electrode active material.

The nanotube of the lithium titanium oxide according to the present invention preferably has a diameter in the range of 10 nm to 1,000 nm, and an aspect ratio (length of the major axis / length of the major axis) is in the range of 3 to 1,000.

Lithium titanium oxide having a nanotube structure of the present invention

A first step of preparing a metastable titanium dioxide (TiO ₂ ) powder,

Reacting the TiO ₂ powder in a LiOH aqueous solution to form a layered titanate containing the Li component by ion exchange;

A third step of heat treating the titanate to convert the layered titanate containing the Li component into a nanotube structure; and

It may be prepared by a method comprising a fourth step of drying the resultant.

1 is a process flow chart for explaining a method for producing a titanate nanotubes according to an embodiment of the present invention. Referring to FIG. 1, the manufacturing method of the present invention begins with preparing a titanium dioxide (TiO ₂ ) powder in a metastable state (S11).

Preparing the titanium dioxide (TiO ₂ ) powder of the metastable state (S11),

i) preparing a titanyl chloride (TiOCl ₂ ) aqueous solution using titanic tetrachloride (TiCl ₄ ),

ii) maintaining the titanyl chloride aqueous solution at a temperature range of about 80 to about 120 ° C. to form a metastable titanium dioxide powder (TiO ₂ );

iii) filtering the titanyl chloride aqueous solution to extract the metastable titanium dioxide powder,

iv) may be implemented by drying the extracted titanium dioxide powder to collect the titanium dioxide powder in the metastable state.

The preparing of the titanyl chloride aqueous solution may include preparing a stabilized titanyl chloride aqueous solution of titanic tetrachloride with ice or ice water and adding water to the titanyl chloride aqueous solution of the first concentration. And diluting to a second concentration lower than the first concentration. Preferably, the first concentration is about 1.5M or more, and the second concentration may be about 0.2 to 1.2M.

In the present invention, in the second step (S12 in FIG. 1) for producing a lithium titanium oxide having a nanotube structure reacts with a strong alkali compound LiOH and the metastable titanium dioxide powder, wherein the LiOH aqueous solution is preferably Has a concentration of about 1 to about 30 M.

In the step (S12), it is allowed to react with the TiO ₂ powder in an aqueous solution of LiOH compound. In this reaction, a part of the titanium dioxide may be substituted with Li to form a titanate having a layered structure containing the Li component of the LiOH compound. That is, in the present step, for example, the TiO ₂ powder reacts in an aqueous LiOH solution, and it can be understood that the Ti-O bond is partially collapsed so that the conversion to the layer structure of Ti-OLi occurs.

In the present invention, a compound which can be used to prepare a lithium titanium oxide having a nano structure is LiOH. Preferably, the aqueous LiOH compound solution may be an aqueous NaOH solution of about 5 to about 30 M. When the concentration of the aqueous LiOH compound is less than 5M, the amount of nanotubes formed is extremely low. On the contrary, when the concentration of the LiOH aqueous solution is greater than 30M, alkali ion supersaturation occurs at room temperature, which is difficult to convert into a homogeneously mixed aqueous solution.

In the third step (S13 of FIG. 1) for preparing a lithium titanium oxide having a nanotube structure of the present invention, the titanate is heat-treated so as to be converted from a layered structure to a nanotube structure.

The heat treatment step is preferably performed for about 10 to about 60 hours at a temperature of about 100 to about 240 ℃. In this heat treatment process, although not clearly identified, it may be understood that the layered titanate is rolled up to form a tube structure by the driving force provided in the heat treatment.

In the heat treatment, nanotubes are formed when a strong alkali solution in which the titanium dioxide particles are dissolved is heated at a high temperature in a reaction vessel in which evaporation is suppressed for a sufficient time, which is called hydrothermal synthesis. In order to form the nanotubes of the present invention, the heating temperature of the LiOH aqueous solution is preferably 100 to 240 ° C. If the heating temperature is less than 100 ℃ it is difficult to expect a sufficient synthesis reaction, so the yield of the nanotubes is significantly reduced, on the contrary, if it exceeds 240 ℃ it is easy to form rods, wires, etc. instead of nanotubes if possible It is good to use within the said temperature range.

In addition, in order to induce a sufficient reaction, the heating time is preferably 10 hours or more. The longer the heating time is, the more the reaction takes place, so the upper limit of the heating time does not need to be particularly limited. However, if the heating time exceeds 60 hours, the effect does not increase any more. It is preferable. The hydrothermal synthesis process is preferably carried out in an autoclave.

Finally, in step S14, the desired titanate nanotubes can be obtained by drying the washed result. In this drying step, the lithium titanium oxide in the form of a desired nanotube can be appropriately obtained by drying for 6 to 12 hours at a temperature of 40 to 60 ° C.

Figure 2 is a process flow diagram for explaining the manufacturing process of the titanium dioxide powder in the metastable state in the first step that can be preferably employed in the present invention.

First, the process of the titanium dioxide powder, according to the registered patent application No. 10-0814951 filed by the applicant, the first step of preparing and diluting the aqueous solution of titanyl chloride (TiOCl ₂ ) with titanic tetrachloride (TiCl ₄ ) (S21) Begins with).

In this step, a method known in the art may be used to obtain an aqueous solution of titanyl chloride at a desired concentration while controlling the instability of the titanic tetrachloride. That is, a process of diluting titanium tetrachloride having very unstable characteristics to an aqueous solution of titanyl chloride having a first concentration stabilized using ice water or ice, and then diluting to a desired second concentration may be used. In this case, the first concentration for obtaining the first stabilized aqueous solution is preferably at least about 1.5 M or more, and the final second concentration required in the subsequent step is preferably in the range of about 0.1 M to 1.0 M.

Subsequently, in the second step S22, the titanyl chloride (TiOCl ₂ ) aqueous solution is maintained at a temperature of 60 to 100 ° C. to form a metastable titanium hydroxide (TiO (OH) ₂ ).

This temperature condition is to prevent the time that the metastable titanium hydroxide is in a metastable state becomes too short. That is, it should be at least 60 ° C or higher, and phase transformation may be performed at 100 ° C or higher. Accordingly, the temperature for obtaining the metastable titanium hydroxide is preferably about 60 to about 100 ° C.

Next, in the third step S23, the titanium hydroxide in a metastable state is extracted. The hydroxide obtained here is passed through a filter paper in the shortest possible time, and the filtered powder is dried in an oven at a temperature of about 60 to about 80 ° C. for about 3 to 6 hours.

In the present invention, in order to further increase the rate characteristic improvement effect, a method of increasing the electron conductivity of the electrode may be used together, which may be achieved by coating the surface of the lithium titanium oxide with carbon or forming a composite.

The method for producing a composite of carbon nanoparticle lithium titanium oxide and carbon may be a method known to those skilled in the art as a method of carbon coating the surface of the inorganic oxide particles, preferably in the present invention nanostructure lithium titanium surface is not coated The oxide may be mixed with carbon such as carbon black to form a composite by ball-milling, or carbon may be coated on particles of nanostructured lithium titanium oxide using an organic material including carbon. By this method, the effect of obtaining a high rate characteristic can be anticipated by increasing the electron conductivity of lithium titanium oxide.

An electrode of a secondary battery using lithium titanium oxide having a nanostructure according to the present invention as an electrode active material may be manufactured by a method known to those skilled in the art. That is, according to the present invention, in addition to using lithium titanium oxide having a nanostructure as an active material, a conductive agent for providing electrical conductivity and a binder that enables adhesion between the material and the current collector may be further used. The paste was prepared by adding and stirring a conductive agent in a weight ratio of 1 to 30 wt% and a binder in a weight ratio of 1 to 10% with respect to the electrode active material prepared by the above method, and then adding the mixture to a dispersant and collecting the metal material. It is applied to the whole, compressed and dried to prepare a laminate electrode.

The conductive agent generally adds carbon black at 1 to 30% by weight based on the total weight. Products currently available as conducting agents include acetylene black series (Chevron Chemical Company or Gulf Oil Company), Ketjen Black EC series (Armak Company ), Vulcan XC-72 (manufactured by Cabot Company) and Super P (manufactured by MMM).

Representative examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF) or copolymers thereof, cellulose, and the like, and representative examples of the dispersant are isopropyl alcohol and N-methylpyrrolidone. (NMP), acetone and the like.

The current collector of the metal material is a metal having high conductivity, and any metal can be used as long as the paste of the material is easily adhered and is not reactive in the voltage range of the battery. Representative examples include meshes, foils, and the like, such as aluminum or stainless steel.

The present invention also provides a secondary battery comprising the electrode of the present invention. The secondary battery of the present invention can be produced using a method known in the art, and is not particularly limited. For example, the separator may be placed between the positive electrode and the negative electrode to add a nonaqueous electrolyte. In addition, the electrode, the separator and the non-aqueous electrolyte and, if necessary, other additives, may be those known in the art.

In addition, a porous separator may be used as a separator in manufacturing a battery of the present invention, and for example, a polypropylene-based, polyethylene-based, or polyolefin-based porous separator may be used, but is not limited thereto.

The nonaqueous electrolyte of the secondary battery that can be used in the present invention may include a cyclic carbonate and a linear carbonate.

Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), gamma butyrolactone (GBL), and the like. Examples of the linear carbonates include one or more selected from the group consisting of diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC) and methyl propyl carbonate (MPC). In addition, the nonaqueous electrolyte of the secondary battery of the present invention contains a lithium salt together with the carbonate compound. Specific examples of lithium salts include LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , and LiN (CF ₃ SO ₂ ) ₂ .

TiO ₂ powder is a starting material of the present invention by the hydrothermal synthesis method of the present invention, lithium titanium oxide used as a secondary battery, in particular, a lithium active material used as a negative electrode active material to increase the specific surface area of the electrode, thereby increasing the diffusion of lithium ions It is possible to improve the rate characteristic of the battery by speeding it up.

When the active material is in the nanostructured form, the diffusion distance of lithium is shortened in the solid, thereby facilitating the diffusion of lithium and reducing the resistance, thereby increasing the rate characteristic of the battery.

In addition, the present invention uses a lithium titanium oxide as a negative electrode active material, such that a large irreversible capacity that can occur when using a carbon-based material (for example, carbon nanotube) as a negative electrode active material is large, such as a decrease in capacity. Problems inherent in carbon materials can also be solved.

Hereinafter, the present invention will be described in more detail with reference to a specific embodiment.

Example 1 Preparation of Titanium Dioxide Powder in Metastable State

In this embodiment, titanic tetrachloride (TiCl ₄ : Aldrich trade name 3N) was mixed with ice water according to the low temperature homogeneous precipitation to prepare a 1.5M aqueous titanyl chloride solution. Then, distilled water was mixed with the aqueous titanyl chloride solution and diluted to 0.67M.

It was maintained at a temperature of about 100 ° C. for 2 hours to form a precipitate of titanium hydroxide. The precipitate was filtered using filter paper to collect and then dried in an oven at 60 ° C. for 6 hours. Through this process, it was possible to obtain a metastable titanium hydroxide.

Example 2 Preparation of Lithium Oxide with Nanotube Structure

The powder obtained in Example 1 was added to 10M LiOH to change the bond between Ti-O-Li to convert into a layered structure, and then maintained at 100 ° C. for 10 hours in an autoclave to form a nanotube structure. The collected powder was dried at 60 ° C. for 12 hours to remove moisture in the powder.

The powder obtained after this process was analyzed through (HRTEM, XRD), and in particular, the crystal structure of Li ₄ Ti ₅ O ₁₂ was proved through XRD.

3 is an X ray diffraction test result of Li ₄ Ti ₅ O ₁₂ prepared through Examples 1 and 2. Unlike the conventional spherical powder, the nanotube type Li ₄ Ti ₅ O ₁₂ maintains a very stable structure, and unlike the conventionally known, it can be seen that the crystal orientation of the nanotube at 10 degrees.

Figure 4 is a high magnification transmission electron microscope photograph of the Li ₄ Ti ₅ O ₁₂ prepared by the present invention. Ni as shown in the picture doped It can be seen that the TNT has a tubular structure with an interlayer distance of 0.74 nm and a length of several hundred nanometers, an outer distance of 10 nm or less, and an inner distance of 5 nm or less.

< Example  3> lithium ion battery Half-cell  Produce

The lithium titanium oxide in the form of nanotubes prepared in Examples 1 and 2 was used as an electrode active material. 2 parts by weight of acetylene black as a conductive agent and 8 parts by weight of PVDF with a binder were added to 90 parts by weight of the material, and added to N-methyl-2-pyrrolidone (NMP) to prepare an electrode slurry, which was then coated on an aluminum (Al) current collector. It applied to and dried, and manufactured the electrode. Using a lithium foil as the counter electrode, a coin half cell was constructed together with the electrode prepared by the above method. A secondary battery was prepared by interposing a polyolefin-based separator between the prepared electrodes and injecting the electrolyte solution.

Powder life characteristics evaluation results of the battery prepared in Example 3 is shown in FIG. As shown in Figure 5 it can be seen that even at 25 cylcle or more it is stably supplying a high capacity of about 250mAh / g, it can be seen that shows a very increased life compared to the conventional.

The rate characteristics of the coin cell are shown in FIG. 5, and FIG. 6 shows the life characteristics of the coin cell.

1 is a process flow chart for explaining a method for producing a titanate nanotubes according to an embodiment of the present invention.

Figure 2 is a process flow diagram for explaining the manufacturing process of the titanium dioxide powder in the metastable state in the first step that can be preferably employed in the present invention.

3 is an X-ray diffraction test result of Li ₄ Ti ₅ O ₁₂ prepared through Examples 1 and 2. FIG.

Figure 4 is a high magnification transmission electron microscope photograph of the Li ₄ Ti ₅ O ₁₂ prepared by the present invention.

5 is a graph showing the life characteristics of the battery prepared in Example 3.

Claims (8)

delete delete delete delete A first step of preparing a metastable titanium dioxide (TiO ₂ ) powder, A _{second step} of reacting the LiOH aqueous solution with the TiO ₂ powder to form a layered titanate containing the Li component by ion exchange; A third step of heat treating the titanate to convert the layered titanate containing the Li component into a nanotube structure; and And a fourth step of drying the heat-treated titanate converted into nanotube structure. The metastable titanium dioxide (TiO ₂ ) powder, i) preparing a titanyl chloride (TiOCl ₂ ) aqueous solution using titanic tetrachloride (TiCl ₄ ), ii) maintaining the titanyl chloride aqueous solution in a temperature range of 80 ~ 120 ℃ to form a titanium dioxide powder (TiO ₂ ) of the metastable state, iii) filtering the titanyl chloride aqueous solution to extract the metastable titanium dioxide powder, and iv) drying the extracted titanium dioxide powder and collecting the titanium dioxide powder in a metastable state. delete The method of claim 5, The concentration of the aqueous LiOH solution is 1 to 30M to prepare a lithium titanium oxide in the form of nanotubes. The method of claim 5, The heat treatment step is a method of producing a lithium titanium oxide in the form of nanotubes which is performed for 10 to 60 hours at a temperature of 100 ~ 240 ℃.

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