KR20130038518A - Method and preparation of lithium titanate/carbon composite materials for lithium ion battery - Google Patents

Abstract

PURPOSE: A Li4Ti5O12/carbon composite material is provided to have high electric conductivity, to charge and discharge high current density, thereby being used as a negative electrode active material for a lithium ion secondary battery and a hybrid capacitor. CONSTITUTION: A Li4Ti5O12/carbon composite material is for a negative electrode material of a secondary battery or hybrid capacitor and is a carbon material using a polymer material is formed on the surface of a Li4Ti5O12 material. A manufacturing method of the Li4Ti5O12/carbon composite material comprises a step of manufacturing a Li4Ti5O12 metal oxide by a sol-gel method; and a step of coating the metal oxide with a polymer material and carbonizing the metal oxide coated with the polymer material.

Description

Lithium titanate / carbon composite material for secondary battery negative electrode material and its manufacturing method {Method and Preparation of Lithium Titanate / Carbon Composite Materials for Lithium ion Battery}

The present invention relates to a composite material for improving the power density of lithium titanate, which is applicable to a negative electrode material of a lithium ion secondary battery and a hybrid capacitor, and a method of manufacturing the same. More specifically, Li ₄ Ti ₅ O ₁₂ (Lithium Titanate) Composite materials suitable for the negative electrode active materials of lithium ion secondary batteries and hybrid capacitors, which can be charged and discharged at high current density with high electrical conductivity by coating carbon materials with polymers and surfactants on their surfaces, and their manufacture It is about a method.

The necessity of the energy storage device due to the development of the electronic devices is emerging. Electronic devices are being miniaturized according to the direction of development, and energy storage devices applied to the electronic devices are developing in the direction of high capacity.

In order to increase the capacity of the energy storage device as described above, Patent No. 10-450548 discloses a first carbon-based component to improve battery efficiency in an area where a battery is actually used while maintaining high charge and discharge efficiency and excellent cycle characteristics. Provided are a negative electrode for a secondary battery having a multilayer structure of a layer and a second layer of an amorphous lithium storage material. However, the patent has a disadvantage that the high output characteristics of the battery is very low by using carbon as a main component.

In addition, Patent Publication No. 2007-4794 discloses nanoscale silicon particles of a negative electrode material for a lithium ion battery, which provides a negative electrode material having a reversible capacitance to provide an electrode material having sufficient mechanical stability during a cycle. To this end, there is disclosed an electrode material consisting of nanoscale silicon particles, conductive carbon black, graphite and a binder. However, there is still a problem regarding the high output characteristics of the battery since the 5-8 wt% of the published patent-excited graphite is used.

Another Patent No. 10-796687 discloses Si and Sn and their oxides, tin alloy composites, in order to provide an active material for a lithium secondary battery having excellent life characteristics and exhibiting high conductivity even when a small amount of conductive material is used. An active material selected from lithium metal nitride and lithium metal oxide, an active material for a lithium secondary battery including a fibrous or carbon conductive material attached to the surface of the active material, and the above materials are mixed to adjust pH and heat treatment at 300 to 450 ° C. Disclosed is a method for manufacturing an active material for a lithium secondary battery and a lithium secondary battery including the same. However, the patent has to be heat treated at a high temperature in the manufacturing method, there will be a problem of economics due to the use of silicon or tin or these oxides or composites.

The present invention solves the problems of the prior art as described above and improves the high output characteristics of the lithium ion secondary battery, and the metal oxide suitable for use as a negative electrode material for a lithium ion secondary battery and a hybrid capacitor to enable charge and discharge at a high current density It is an object of the present invention to provide a composite material and a method for manufacturing the same, which can have rapid charge and discharge characteristics through carbon composite with lithium titanate.

The present invention is to use as a negative electrode material of a secondary battery or a hybrid capacitor in order to achieve the object of the present invention as described above Li ₄ Ti ₅ O ₁₂ Li ₄ Ti ₅ formed of a carbon material using a polymer material on the surface of the material Provides O ₁₂ / carbon composites.

To the invention it is also to provide the composite material, Li ₄ Ti ₅ O to prepare a ₁₂ materials and then by carbonizing using a polymer material to the material Li ₄ Ti ₅ O _12, the carbon material is formed on the material surface Li ₄ Ti ₅ O ₁₂ / Provides a method for producing a carbon composite material.

In the above Li ₄ Ti ₅ O ₁₂ metal oxide is performed by a sol-gel (Sol-Gel) method, in order to produce the metal oxide,

Lithium Hydroxide (LiOH), Monohydrate (Monohydrate; LiOH H ₂ O), Lithium acetate dihydrate (C ₂ H ₃ O ₂ Li ₂ H ₂ O) any one selected from Dissolving the lithium salt in a 1:50 to 100 weight ratio in distilled water to prepare a first solution (S10);

Preparing a second solution by dissolving TTIP (tetra titanium iso-propoxide) in a solvent at a weight ratio of 1:50 to 100 (S20);

A step (S30) of preparing a third solution in which the first solution and the second solution are mixed;

Adding ultrasonic waves to the third solution to increase dispersibility (S40);

Heating to form a gel, aging step (S50);

Filter step (S60) for solvent removal; And

It provides a method for producing a Li ₄ Ti ₅ O ₁₂ metal oxide comprising a step S (70) of the above material for imparting crystallinity.

The concentration of the lithium salt in the step (S10) is preferably a weight ratio of the corresponding concentration 1:50 ~ 100, the weight ratio of less than 50 has the disadvantage that lithium is not included in the crystallinity of the preparation material, the weight ratio of 100 or more This is because there is a problem that unreacted precipitation may be formed in relation to the solubility of lithium salts. In addition, the solvent used is preferably to use distilled water to prevent impurities.

The solvent used in the step (S20) may be used at least one selected from 2-methoxy ethanol, iso-propanol, ethanol, and the starting material Therefore, it is preferable to use iso-propanol because the solidification of TTIP may proceed and may be affected by the temperature conditions.

In addition, in the above step (S30), the mixing ratio of Li: Ti is preferably mixed in a molar ratio of 4.5: 5. If lithium is added in an excessive amount, unreacted products may be precipitated and the target metal may be added in a small amount. This is because the crystallinity of the oxide may not be achieved and the crystallinity of the TiO ₂ may act as a cause of deterioration of the cycle performance of the final object.

In addition, in the step (S40), the ultrasonic wave is increased in dispersion by irradiating the ultrasonic wave for 4 hours or more in a frequency range of 20 kHz to 70 kHz. When the frequency range is less than 20 kHz, there is a problem in that the size of the particles is large due to failure to maintain a constant dispersibility of the sol state, and when it exceeds 70 kHz, there is a problem of inhibiting crystal formation due to the high frequency. It is desirable to keep the frequency in the range of 20 kHz to 70 kHz. In addition, when the irradiation time is less than 4 hours, there is a problem that does not have the same dispersibility of the sol state as described above, if it exceeds 6 hours acts as a factor that lowers the efficiency.

In addition, the temperature rise temperature in the above step (S50) is affected by the choice of the solvent should not exceed 80 ℃. In addition, the exposure time in the temperature increase step is affected by the temperature conditions, the room temperature is the most uniform, but due to the working limit is preferred between about 50 ~ 80 ℃, the transition time to gel state below 50 ℃ has more than 12 hours The closer to 80 ° C, the faster the crystallization. However, as the temperature approaches 80 ° C, an amorphous phase may appear, which is most advantageous for forming particles at 50 ° C.

The firing step (S70) is carried out through a filter step (S60) to remove the solvent and the firing conditions are appropriately about 800 ℃ ~ 900 ℃. When the firing temperature in the firing step is less than 800 ° C., the formation of TiO ₂ , which is the main supporting material of LTO, does not form a spinel form, and forms a rutile structure or an anatase structure at the same time. . The LTO, which does not form a spinel structure, has a problem in that its irreversible capacity is increased and its reactivity is lowered, and when it exceeds 900 ° C., the crystalline form of LTO does not form a spinel structure and is similar to that of the TiO ₂ formation process. Since there may be a problem to increase the irreversible capacity to proceed to, the firing temperature is preferably made in the range of 800 ~ 900 ℃.

In another aspect, the present invention, in order to form a carbon material by carbonizing the polymer coated on the Li ₄ Ti ₅ O ₁₂ material prepared as described above,

Dissolving the polymer and the surfactant in a solvent to prepare a fourth solution (SS10);

Preparing a fifth solution by adding the prepared Li ₄ Ti ₅ O ₁₂ (S220),

Ultrasonic step (SS30) to increase the dispersibility of the polymer and surfactant and to enhance the surface adsorption characteristics of Li ₄ Ti ₅ O ₁₂ ;

Drying of the solvent (SS40);

Sulfuric acid addition and heating step (SS50) for the carbonization process;

Washing step (SS60) for drying process and removal of unreacted material; And

It provides a method consisting of a firing step (SS70) for surface functional group removal and impurities removal.

The solvent used in the step of preparing the fourth solution (SS10) is water or alcohol-based which can disperse the polymer and the surfactant is appropriate, and if the carbonized material is a polymer is more alcohol-based than difficult to maintain the dispersed phase 2-propanol or other organic solvents may be used, and in the case of surfactants, water may be used. The concentration of the fourth solution to be prepared is determined according to the amount of carbon material to be coated on the surface of Li ₄ Ti ₅ O _12. The lower the concentration is, the more uniform the coating conditions are. . The fourth solution containing more than 30wt% of polymer causes problems of inhibiting the dispersibility of Li ₄ Ti ₅ O ₁₂ material and suppressing the performance improvement of Li ₄ Ti ₅ O ₁₂ by coating excess carbon material on the surface. . In addition, the polymer to be applied is preferably a polymer having a MW (molecular weight) of 3000 to 7000, and in order to suppress the inclusion of impurities, it is preferable to use only a polymer composed of C, N, O, and H. When the molecular weight is 3,000 or less, Li ₄ Ti ₅ O ₁₂ has a small area to be coated in the process of carbonization loss, and more than 7,000 is applied larger than the particle size of Li ₄ Ti ₅ O ₁₂ has a difficulty in forming the particle size. In addition, as the surfactant, nonionic surfactants are advantageous for preventing impurities, and the application of nitrogen-based nonionic surfactants is also possible. In the case of the fatty acid surfactant, the molecular weight is not large, and thus, the characteristics are similar to those of the polymer.

Li ₄ Ti ₅ O was added to ₁₂ the weight ratio of Li ₄ Ti ₅ O ₁₂ are added in step (SS20) for preparing the fifth solution is determined by the amount of polymer to be coated on the surface as the ratio of the The proportion of phosphorus polymer is added so as not to exceed 30 wt%.

Ultrasonic irradiation step (SS30) is performed to improve the dispersibility of Li ₄ Ti ₅ O ₁₂ and the carbonized material and the surfactant contained in the fifth solution, the irradiation time is appropriate from 1 hour to 3 hours, Irradiation time of less than 1 hour is not effective and has the disadvantage that the coagulation effect characteristics are enhanced than the dispersion effect due to the ultrasonic wave in more than 3 hours. In addition, the irradiated ultrasound is performed under the same conditions as the step (S40).

In addition, the drying step (SS40) of the solvent is drying the selected solvent in the range not exceeding the boiling point and the stirring process is essentially performed to prevent the aggregation phenomenon in the drying process. Due to the boiling point of the solvent in the drying process or due to the adjacent temperature conditions, it is impossible to form an even surface due to the flocculation phenomenon of the carbonized material when bubbles are generated.

The carbonization step (SS50) is performed through the above steps, and about 10 wt% of concentrated sulfuric acid (more than 98%) is added based on the solid content ratio. The added sulfuric acid undergoes dehydration, undergoes carbonization of the polymer on the surface of Li ₄ Ti ₅ O ₁₂ , and contains minimal moisture in the drying process to increase the efficiency in the carbonization process. It is preferable to simultaneously carry out the stirring process while maintaining the carbonization process under the conditions of 160 ° C. or less, and there may be a loss of the surrounding equipment at a high temperature of 200 ° C. or more. In addition, the execution time is preferably about 2 hours to 3 hours, and the conditions under 2 hours are unreacted, and if more than 3 hours, the carbon formed on the surface is burned, causing a decrease in efficiency.

In order to remove impurities in the material produced through the carbonization process (SS50), the water is washed with dilute hydrochloric acid or sulfuric acid of 10wt% or less, followed by washing with distilled water until the pH of the washing water reaches 7 And to remove the unreacted material (SS60).

In order to remove and stabilize the surface functional group of the material having passed the above step, the firing process is performed under the condition that the carbonaceous material on the surface does not burn, and the condition is performed under the condition of 350 hours or less at 2 hours or less. At the temperature of 350 ° C. or higher, it is excellent in removing impurities through the combustion of impurities, but has the disadvantage of starting combustion of carbon coated on the surface. The lower the firing conditions, the more the application time can be adjusted within 2 hours.

According to the present invention, the prepared Li ₄ Ti ₅ O ₁₂ / carbon composite material has a lower capacity than a single material of the conventional Li ₄ Ti ₅ O ₁₂ , but the charge and discharge characteristics at a higher current density than a single LTO material This has the effect of being applicable as a negative electrode material of a lithium ion secondary battery requiring a large current discharge characteristic and a hybrid capacitor requiring energy density improvement.

1 is a schematic diagram of the effect obtained by coating a carbon material on the required Li ₄ Ti ₅ O ₁₂ material of the invention.
2 is (a) an electrochemical evaluation result of the embodiment of Li ₄ Ti ₅ O ₁₂ , (b) is an electrochemical evaluation result of the Li ₄ Ti ₅ O ₁₂ / carbon material.
Figure 3 is a graph of Figure ₄ of Li ₄ Ti ₅ O ₁₂ , Li ₄ Ti ₅ O ₁₂ / carbon and the comparison result of the capacitance reduction rate according to the C-rate change.

[Example]

After mixing the composite material and the binder prepared under the conditions in the above steps to prepare a slurry, the electrode is subjected to the coating process after producing an electrode coated with a 20 ~ 100㎛ thickness on aluminum foil of 10 ~ 20㎛ thickness Is used as a cathode and a lithium cell is used as a counter electrode to produce a coin-cell to conduct constant current charge and discharge.

In the manufacture of the coin-cell, the manufactured electrode is cut into a unit area of 2 cm 2 by using a punching machine having a diameter of 16 mm, and welded to a coin-cell (2016; 20 mm (diameter x 1.6 mm (size) size of coin type)). The prepared electrode is dried again at 180 ° C., and then assembled as a cell by impregnating a counter electrode Lithium-disk and electrolyte 1M LiBF ₄ / PC in an argon atmosphere glove box (water content of 0.3 ppm or less).

Lithium titanate powder was prepared using LiOH and TTIP through step (S10) to step (S70). In order to perform the steps (SS10 ~ SS60), 0.2 g of Pluronic P123, a nonionic surfactant, was stirred in 100 ml of distilled water at room temperature for 6 hours. Thereafter, 1.2 g of lithium titanate powder was added, followed by stirring at 80 ° C. for 30 minutes. After the drying process, ml of sulfuric acid was added and carbonized with stirring at 160 ° C. The electrochemical properties were evaluated using the method of the above (S310 ~ S320), which is an electrochemical property evaluation method using the Li 4 Ti 5 O 12 / carbon composite material prepared through the process, and the results are shown in FIG. 2. In Figure 3 showing the charge and discharge results shown in Figure 2 can be confirmed through the reduction rate of the capacitance according to the C-rate change. Existing LTO single material can be seen that the reduction rate of discharge amount by the change of current amount is sharply reduced after 5C, but LTO / carbon composite material shows higher residual capacity than conventional LTO. As a result, the characteristics of the high current density of the manufactured LTO / carbon materials have been enhanced, and high power density can be maintained.

Claims (16)

As for use as a secondary battery or the negative electrode material of a hybrid _{capacitor, Li 4 Ti 5 O 12 Li} 4 Ti 5 O 12 / carbon composite material formed of a carbon material with a polymer material on the surface. As a manufacturing method of Li ₄ Ti ₅ O ₁₂ / carbon composite material,
Li ₄ Ti ₅ O _{12 The} metal oxide is prepared by the sol-gel method, and then coated with a polymer material on the metal oxide to carbonize the method of manufacturing a Li ₄ Ti ₅ O ₁₂ / carbon composite material. The method of claim 2, wherein the Li ₄ Ti ₅ O ₁₂ metal oxide is;
To prepare oxides,
Lithium Hydroxide (LiOH), Monohydrate (Monohydrate; LiOH H ₂ O), Lithium acetate dihydrate (C ₂ H ₃ O ₂ Li ₂ H ₂ O) any one selected from Dissolving the lithium salt in a 1:50 to 100 weight ratio in distilled water to prepare a first solution (S10);
Preparing a second solution by dissolving TTIP (tetra titanium iso-propoxide) in a solvent at a weight ratio of 1:50 to 100 (S20);
A step (S30) of preparing a third solution in which the first solution and the second solution are mixed;
Increasing ultrasonic dispersion to the third solution by ultrasonic waves (S40);
Heating to form a gel, aging step (S50);
Filter step (S60) for solvent removal; And
Method for producing a Li ₄ Ti ₅ O ₁₂ / carbon composite material, characterized in that it is manufactured by a method comprising the step S (70) of firing the material for the crystallinity. The method of claim 3 wherein the solvent in step (S20) is 2-methoxy ethanol, iso-propanol, Li ₄ Ti ₅ O ₁₂ / The method of producing a carbon composite material characterized in that at least one member selected from ethanol. The method of claim 3, wherein the mixing in the step (S30) was Li: Li ₄ Ti ₅ O ₁₂ / The method of producing a carbon composite material, characterized in the works, at a ratio of 5: Ti ratio of 4.5 in molar ratio. The method of claim 3, wherein the ultrasonic wave in the step (S40) is 20 ~ 70kHz, the irradiation is 4 ~ 6 hours, the method of manufacturing a Li ₄ Ti ₅ O ₁₂ / carbon composite material. The method of claim 3, wherein the temperature rise in the step (S50) is 50 ~ 80 ℃ manufacturing method of Li ₄ Ti ₅ O ₁₂ / carbon composite material. 4. The method of claim 3, Li ₄ Ti ₅ O ₁₂ / The method of producing a carbon composite material that the firing in the step (S70) characterized in that performing at 800 ~ 900 ℃. The method of claim 2, wherein the metal oxide is coated with a polymer material and carbonized.
Dissolving the polymer and the surfactant in a solvent to prepare a fourth solution (SS10);
Preparing a fifth solution by adding the prepared Li ₄ Ti ₅ O ₁₂ (S220),
Ultrasonic irradiation step (SS30) to increase the dispersibility of the polymer and surfactant and to enhance the surface adsorption characteristics of Li ₄ Ti ₅ O ₁₂ ;
Drying of the solvent (SS40);
Sulfuric acid addition and heating step (SS50) for the carbonization process;
Washing step (SS60) for drying process and removal of unreacted material; And
Carbonization method characterized in that consisting of a firing step (SS70) for removing the surface functional groups and impurities. 10. The method of claim 9, wherein the solvent in the step (SS10) is water, alcohol or organic solvent, characterized in that the manufacturing method of Li ₄ Ti ₅ O ₁₂ / carbon composite material. The method of claim 9, wherein the polymer in step (S10) has a molecular weight of between 3,000 ~ 7,000 Li ₄ Ti ₅ O ₁₂ / carbon composite material manufacturing method. The method of claim 9, wherein the addition of the Li ₄ Ti ₅ O ₁₂ in the step (SS20) is Li ₄ Ti ₅ O ₁₂ / The method of producing a carbon composite material, characterized in that the following is presented a 30wt% polymer ratio. The method of claim 9, wherein the ultrasonic irradiation in the step (SS30) is irradiated for 1 to 3 hours at 20 ~ 70kHz method of manufacturing a Li ₄ Ti ₅ O ₁₂ / carbon composite material. 10. The method of claim 9, wherein the addition of sulfuric acid in the step (SS50) is 10wt% based on the solid content ratio, the temperature rise is 160 ~ 200 ℃ and the running time is Li ₄ Ti ₅ O ₁₂ / carbon, characterized in that 2 to 3 hours Manufacturing method of composite material. 10. The method of claim 9, Li ₄ Ti ₅ O ₁₂ / The method of producing a carbon composite material, characterized in that washing is performed at said step (SS60) is a diluted hydrochloric acid of less than 10wt%. 10. The method of claim 9, Li ₄ Ti ₅ O ₁₂ / The method of producing a carbon composite material, characterized in that the calcination in step (SS70) is performed at less than 350 ℃ less than 2 hours.

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