KR100784637B1 - Synthetic method of lithium titanate spinel oxide material using a li based molten salt - Google Patents

Abstract

A method for preparing lithium spinel titanate powder using a molten lithium salt is provided to simplify the overall process as compared with conventional wet processes, to prevent environmental pollution and generation of a significant amount of byproducts, and to obtain a useful electrode active material. A method for preparing lithium spinel titanate powder using a molten lithium salt comprises the steps of: (1) mixing lithium salt powder including lithium oxide with titanium oxide powder; (2) firing the mixed powder obtained from step (1) at a temperature higher than the melting point of the lithium salt; and (3) washing and drying the powder obtained from step (2). The lithium salt used in step (1) includes a lithium salt capable of melting lithium oxide at a temperature of 850 deg.C or lower.

Description

Synthetic method of lithium titanate spinel oxide material using a Li based molten salt}

1 shows a method for producing the lithium titanate spinel powder of the present invention,

2 shows an X-ray diffraction pattern of lithium titanate spinel powder according to an embodiment of the present invention.

The present invention relates to a method for producing lithium titanate spinel powder using a lithium molten salt, and in particular, by the reaction of the lithium salt and titanium oxide at a temperature above the melting point of the salt, the complexity of the process caused by the conventional wet reaction method, the environment by-product Lithium titanate using lithium-based molten salt which can be used as positive and negative electrode materials for energy storage devices such as lithium secondary batteries, overcoming disadvantages such as burdens, by-products in the solid-phase reaction method, and high temperature reaction temperature It is about the manufacturing method of a spinel powder.

Primary batteries literally refer to batteries that cannot be reused, that is, used once and discarded, and secondary batteries refer to batteries that can be recharged once and used multiple times. Among the rechargeable secondary batteries, the most popular battery is a lithium secondary battery. Lithium secondary batteries include high performance lithium secondary batteries, electric motors, and hybrid electric vehicles used as energy sources for mobile information and communication devices such as mobile phones, PDAs (Personal Digital Assistants), MP3 players, camcorders, and notebook computers; It is widely applicable to secondary batteries for high output large transport equipment such as HEV). In particular, the trend toward miniaturization and light weight of portable electronic devices such as notebooks and mobile phones has further promoted research on lithium secondary batteries having high energy density.

Specifically, the lithium secondary battery includes a cathode / cathode active material, a current collector, and an electrolyte. The cathode / cathode active material generates electricity, and a lithium-containing composite oxide, preferably a lithium-transition metal oxide, is used as the cathode active material. As the negative electrode active material, lithium metal, lithium alloy, carbon (crystalline or amorphous) or carbon composite material is used. The current collector uses a metal current collector as a passage through which electrons generated and supplied to the active material can move. In addition, the electrolyte serves as a medium for ion conduction, and consists of a non-aqueous solvent, lithium salt, and other additives.

The lithium secondary battery utilizes electrical energy generated by an oxidation / reduction reaction occurring during intercalation and deintercalation of lithium ions at the positive and negative electrodes. Generally, lithium metal and carbon are used as an anode material of a lithium secondary battery, and transition metal oxides such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are used as a cathode material. However, LiNiO ₂ has a large charging capacity, but is difficult to synthesize, and LiMn ₂ O ₄ has a small capacity. In addition, LiCoO _{2, the} most widely used cathode material of lithium secondary batteries, has been reported to have a rapidly deteriorated battery performance when lithium ions are desorbed in a specific region (x> 0.5, Li _{1 - x} CoO ₂ ).

Except for lithium cobalt oxide (LiCoO ₂ ), which is currently used in Korea, the development of other high-capacity or high-output cathode materials is somewhat inferior to Japan. Particularly, it is a compound represented by AB ₂ O ₄ , which is attracting attention as a cathode material for HEV batteries because it is cheaper and has higher output characteristics than the existing LiCoO ₂ . Although it is not mass produced, spinel-based cathode materials are in the spotlight as cathode materials for batteries because of their low cost and high output characteristics.

On the other hand, spinel type Li ₄ Ti ₅ O ₁₂ is a material that exhibits excellent insertion and desorption reversibility in the charge / discharge cycle represented by the following equation because it is stable in charge and discharge, and also does not cause structural changes as lithium enters and exits (Zero -Strain Insertion Material of Li [Li _1/3 Ti _5/3 ] O ₄ for Rechargeable Lithium Cells, T. Ohzuku, A. Ueda, N. Yamamoto, Journal of the Electrochemical Society, V. 142, p. 1431-1435 , 1995).

Li ₄ Ti ₅ O ₁₂ + 3Li ⁺ + 3e ^- ↔ Li ₇ Ti ₅ O ₁₂ E = ~ 1.5 V

Therefore, Li ₄ Ti ₅ O ₁₂ is a promising positive electrode material and can be connected to a lithium metal negative electrode to construct a secondary battery. In addition, when Li ₄ Ti ₅ O ₁₂ is used as a negative electrode connected to a 4V electrode such as LiMn ₂ O ₄ or LiCoO ₂ , a battery having a voltage of about 2.5 V may be provided.

Conventionally, many studies have been conducted on the use of Li ₄ Ti ₅ O ₁₂ or a method for manufacturing the same as an electrode material for a lithium secondary battery. For example, Japanese Laid-Open Patent Publication No. 2001-243950 discloses a method for producing a negative electrode material for lithium secondary battery of surface-modified carbon coated with spinel-type lithium titanium oxide, and in 1999-283624, lithium hydroxide or the like is used for the negative electrode. Lithium titanium oxides having a crystal structure of are known. In addition, Japanese Patent Laid-Open No. 2001-240498 discloses a method for producing lithium titanate having high crystallinity using lithium oxide and a titanium compound, and Canadian Patent No. 245585 is prepared from a mixed solution of a compound containing titanium and lithium. Li ₄ Ti ₅ O ₁₂ manufacturing process has been reported. In the paper, Hao et al. Studied Li ₄ Ti ₅ O ₁₂ prepared by the sol-gel method using oxalic acid as a chelate reagent in tetrabutoxytitanium (Ti (OC ₄ H ₉ ) ₄ ) and lithium carbonate (Li ₂ CO ₃ ). Has been reported (Hao, YJ et al., Journal of power sources, 158 (2 SPEC.ISS), 1358-1364, 2006), and the internal gel (TiCl ₄ ) as a raw material by Gao et al. Inner gel) has been reported for the fabrication and properties of high density spherical Li ₄ Ti ₅ O ₁₂ anode material prepared by the method (Gao, J. et al., Journal of power sources, 155 (2), 364-367, 2006).

As described above, the conventional manufacturing method for preparing the spinel type Li ₄ Ti ₅ O ₁₂ is largely divided into two phases, a liquid phase reaction method and a solid phase reaction method. The liquid phase reaction method comprises the steps of: i) preparing a mixed solution of a compound containing titanium and lithium, ii) adding a chelating agent to the mixed solution prepared in the above step to make a gel, and iii) the gel prepared in the above step. Heat treatment and pulverizing (WO 2003/012901, US Patent No. 2004/0217335). However, while the liquid phase reaction method can produce lithium titanate having a relatively high crystallinity, the process is complicated and the waste water treatment is difficult, resulting in environmental problems. In addition, the solid-phase reaction method comprises the steps of i) mixing the compound containing titanium and lithium, ii) heat treating and pulverizing the mixture prepared in the above step. For such a solid state reaction process is a by-product other than the Li ₄ Ti ₅ O ₁₂ phase that a simple one object is generated, and the lithium is volatile and difficult to control the atomic ratio of titanium and lithium, efficiently Li ₄ Ti ₅ O ₁₂ Difficult to produce

On the other hand, as a kind of solid-phase reaction method, the primary sintering is performed at a temperature of 600 ° C. or higher and 800 ° C. or lower, and then the secondary sintering is performed at a temperature of 800 ° C. or higher and 950 ° C. or lower to form a Li ₄ Ti ₅ O ₁₂ single phase. Research is underway to prepare the (US Pat. No. 6,654,673). In addition, attempts have been made to produce Li ₄ Ti ₅ O ₁₂ by evaporating and sintering the liquid components in a solution containing titanium and lithium, and then re-firing the powder (US Patent 6,890,510). However, these methods also have the disadvantages of complicated process and low productivity.

On the other hand, the molten salt synthesis (Molten Salt Synthesis) is known as one of the simplest way can be synthesized in a stoichiometric bijeok pure multicomponent oxide powder (Molten Salt Synthesis of a Complex Perovskite , Pb (Fe 0 .5 Nb 0 _.5 ) O ₃ , CC Chiu, CC Li, SB Desu, Journal of the American Ceramic Society, V 74, p. 38-41, 1991). In this case, the molten salt serves as a solvent, a reactant, or both. In general, since the reactants have a very fast diffusion rate in the molten salt, the molten salt synthesis method is much faster than the solid phase reaction method.

Conventionally, conversion of titanium oxide (TiO ₂ ) to Li ₄ Ti ₅ O ₁₂ using a molten salt synthesis method has been attempted by first reacting titanium oxide powder with LiCl or Li ₂ CO ₃ powder. The melting points of LiCl and Li ₂ CO ₃ are 613 ° C. and 730 ° C., respectively, and the lithium salt is volatilized at a temperature of 850 ° C. or higher. Therefore, the synthesis of Li ₄ Ti ₅ O ₁₂ is carried out in the temperature range from the melting point of the salt up to 850 ℃. In addition, the reaction time is limited to 2 hours to overcome the time-dependent particle growth and thus the powder coarsening. In LiCl, however, Li ₄ Ti ₅ O ₁₂ was the main product, but unreacted titanium oxide was also observed. In Li ₂ CO ₃ , unreacted titanium oxide was not observed, but the main product was Li ₂ TiO ₃ .

Binary salts using LiCl and Li ₂ CO ₃ have also been studied. Salts containing 31.2 mol% of Li ₂ CO ₃ in LiCl have a eutectic point of 517 ° C. When the mixed salt powder was reacted with the titanium oxide powder, the presence of unreacted titanium oxide was not observed even at the reaction temperature of 650 ° C., but there was still a problem that the main product was Li ₂ TiO ₃ .

Therefore, the inventors of the present invention, while researching dissimilar metal compounds in order to solve the technical and economical problems of the prior art, by discovering a synthesis method with a high reaction rate, high productivity and low by-products, salts containing titanium and titanium oxide The reaction was carried out at a temperature above the melting point of the salt to efficiently produce a spinel type Li ₄ Ti ₅ O ₁₂ powder to complete the present invention.

Accordingly, an object of the present invention is to provide a method for preparing pure Li ₄ Ti ₅ O ₁₂ powder using a salt containing lithium and titanium oxide.

In order to achieve the above object, the present invention comprises the steps of mixing a lithium salt powder and titanium oxide powder containing lithium oxide (step 1); Calcining the mixed powder obtained in step 1 at a temperature equal to or higher than the melting point of the lithium salt (step 2); And it provides a method for producing lithium titanate spinel powder using a lithium-based molten salt comprising the step (step 3) of washing and drying the powder produced in step 2.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention includes a method for producing lithium titanate spinel powder using a lithium-based molten salt.

Specifically, the present invention comprises the steps of mixing the lithium-based salt powder and lithium oxide powder containing lithium oxide (step 1); Firing the mixed powder obtained in step 1 at a temperature equal to or higher than the melting point of the lithium salt (step 2); And a method of preparing lithium titanate spinel powder using a lithium-based molten salt, which comprises the step of washing and drying the powder produced in step 2 (step 3).

Referring to Figure 1 describes a process for producing a single-phase lithium titanate spinel powder according to the present invention by molten salt synthesis method as follows.

In order to prepare dissimilar metal oxides of lithium and titanium, first, a lithium salt and a titanium oxide powder are mixed at a predetermined ratio. The mixed powder is fired, but is melted at a temperature above the melting point of the salt within a range in which volatilization of the lithium salt does not occur. The time should be as short as possible in order to prevent powder coarsening which increases in particle size in time. After firing, the powder undergoes a washing process, at which time unreacted substances and gases generated during firing are removed. Finally, lithium titanate (Li ₄ Ti ₅ O ₁₂ ) spinel powder may be obtained by drying.

Hereinafter, the present invention will be described in detail step by step.

In the method for preparing a lithium titanate spinel powder of the present invention, step 1 is a step of mixing a lithium salt powder and a titanium oxide powder containing lithium oxide.

The lithium salt containing lithium oxide may be any salt or use as long as it is a lithium salt capable of dissolving lithium oxide (Li ₂ O) at a temperature at which the lithium salt is easily volatilized (for example, 850 ° C.). It is possible. For example, lithium chloride, lithium carbonate (Li ₂ CO ₃ ), lithium chloride-lithium carbonate (Li ₂ CO ₃ ), and the like are preferable, and lithium chloride (LiCl) is more preferable. The melting point of lithium oxide is 1570 ° C. Lithium oxide must be used with a suitable salt to apply molten salt synthesis. The melting point of the LiCl is 613 ° C to dissolve lithium oxide below 850 ° C. In addition, when using the lithium chloride powder containing lithium oxide, the generation of unreacted products or by-products that are a problem when mixing a conventional lithium-based salt (for example, LiCl or Li ₂ CO ₃ ) powder and titanium oxide powder Can be solved.

The lithium oxide is preferably added within the solubility range in LiCl. The solubility of lithium oxide in LiCl is 12 mol% and 16 mol% at 650 ° C and 750 ° C, respectively. Therefore, the content of lithium oxide is more preferably 0.136 mol to 0.19 mol with respect to 1 mol of lithium chloride. If excess lithium oxide is mixed than the solubility of LiCl, lithium oxide that did not participate in the Li ₄ Ti ₅ O ₁₂ synthesis must be removed in a subsequent washing step. However, as the lithium oxide concentration in the LiCl molten salt increased, it was found to be advantageous for the formation of Li ₄ Ti ₅ O ₁₂ . Therefore, the concentration of lithium oxide added to LiCl is preferably as high as possible within the solubility range in LiCl.

The mixing ratio of the lithium salt powder and the titanium oxide powder is preferably 1: 1.3 to 1: 4.0 in a molar ratio of titanium and lithium. More preferably, it is 1: 1.5-1: 2.0. At this time, the molar ratio of titanium and lithium is suitable in consideration of the volatilization of lithium and the contact of lithium-based salt and titanium oxide powder in the firing process. When mixed with less than 1.3 mole of lithium with respect to the titanium per mol, Li ₄ Ti ₅ O ₁₂ structure that produce lithium cap necessary for a small amount of lithium-based salt sufficient titanium oxide powder by the lithium volatilization of the sintering process, and There is a problem that can not be contacted, and when lithium is mixed in excess of 4.0 moles, there is a problem that the excess lithium salt that did not participate in the reaction must be removed by washing or the like in a subsequent step.

In the method for producing a lithium titanate spinel powder of the present invention, step 2 is a step of baking the mixed powder obtained in step 1 at a temperature above the melting point of the lithium salt.

The firing temperature should be balanced between the temperature above the melting point of the salt, which is a limitation of the nature of the molten salt synthesis method, and the temperature at which the salt does not evaporate excessively. When using a lithium salt in which lithium oxide is dissolved in LiCl, May be performed at 650 ° C. to 850 ° C. in the atmosphere, and more preferably at 700 ° C. to 750 ° C. At a temperature below 650 ° C., the lithium salt does not melt and cannot be applied to the molten salt synthesis method. At a temperature of 850 ° C. or higher, the lithium salt is volatilized.

The baking time is preferably limited to 0.5 hours to 6 hours, more preferably 2 hours or less. It is possible to prevent powder coarsening due to time-dependent particle growth when firing within the time range. When the firing temperature is high, the firing time can be shortened, and when the firing temperature is low, the firing time can be adjusted long.

In the method for producing a lithium titanate spinel powder of the present invention, step 3 is a step of washing and drying the powder produced in step 2.

Through the above step, anion products such as Cl ₂ , CO ₂ gas generated in the calcining process of step 2 may be separated from the synthesized powder. In addition, in this process, all of the lithium salts that do not participate in the generation of Li ₄ Ti ₅ O ₁₂ are removed. The washing process is carried out with pure water, until the wash solution is neutral, and the powder washed with pure water is dried.

Lithium titanate (Li ₄ Ti ₅ O ₁₂ ) spinel powder prepared according to an embodiment of the present invention can be analyzed by XRD (X-ray diffraction) to confirm the synthesis, unreacted oxidation as shown in FIG. It can be seen that it consists of a pure Li ₄ Ti ₅ O ₁₂ phase without the formation of titanium or by-products.

Hereinafter, the present invention will be described in detail through examples and drawings. However, the following examples and drawings are merely illustrative of the present invention, and the content of the present invention is not limited by the following examples.

Example 1 Preparation of Li ₄ Ti ₅ O ₁₂ Using LiCl and Li ₂ O 1

High purity rutile TiO ₂ (10 g), LiCl (9.025 g) and Li ₂ O (1.023 g) fine powders were mixed well in an argon gas atmosphere as a starting material for Li ₄ Ti ₅ O ₁₂ synthesis. . The mixed powder was placed in a crucible and calcined at 750 ° C. for 2 hours. The calcined powder was cooled to room temperature, the product was washed with pure water and dried in vacuo to prepare Li ₄ Ti ₅ O ₁₂ .

X-ray diffraction (XRD) analysis was performed to confirm Li ₄ Ti ₅ O ₁₂ prepared in Example 1, and the results are shown in FIG. 2 .

2, the prepared powder can be seen that consists of a pure Li ₄ Ti ₅ O ₁₂ phase which satisfies the spinel structure of the composition formula _{Li [Li 1/3 Ti 5} /3] O 4.

Example 2 Preparation of Li ₄ Ti ₅ O ₁₂ Using LiCl and Li ₂ O 2

High purity rutile TiO ₂ (10 g), LiCl (15.37 g) and Li ₂ O (2.06 g) fine powders were mixed well in an argon gas atmosphere as a starting material for the synthesis of Li ₄ Ti ₅ O _12. . The mixed powder was placed in a crucible and calcined at 800 ° C. for 1.5 hours. After firing, the powder was cooled to room temperature, and the product was washed with pure water and dried in vacuo to form Li ₄ Ti ₅ O _12. Won the award.

In Example 2, the firing time was shorter at a slightly higher temperature than Example 1 to prepare Li ₄ Ti ₅ O ₁₂ powder having a pure spinel structure.

Comparative Example 1 Preparation of Binary Salt Using LiCl and Li ₂ CO ₃

High purity rutile TiO ₂ (10 g), LiCl (19.48 g) and Li ₂ CO ₃ (15.40 g) fine powders were well mixed in an argon gas atmosphere as a starting material. The mixed powder was placed in a crucible and calcined at 750 ° C. for 2 hours. After the calcined powder was cooled to room temperature, the product was washed with pure water and dried in vacuo. The main product was Li ₂ TiO ₃ and a small amount of LiTiO ₂ phase was observed.

As a result of preparing a bicomponent salt powder using Li ₂ CO ₃ which is widely used in the conventional molten salt synthesis method instead of the lithium dioxide of the present invention, LiCl and Li ₂ CO ₃ mixed salt powder was reacted with titanium oxide powder to react at 750 ° C. Firing at temperature gave Li ₂ TiO ₃ powder which is an unwanted compound as a main product.

As described above, according to the present invention, a conventional wet reaction is carried out by reacting a lithium salt containing lithium oxide and titanium oxide at a temperature higher than the melting point of the salt by a method for producing Li ₄ Ti ₅ O ₁₂ , which is a lithium titanate spinel oxide. Overcoming disadvantages such as process complexity caused by the law, environmental burden by by-products, and disadvantages such as by-product generation and high temperature reaction temperature in solid-state reaction method, positive and negative electrodes of energy storage devices such as lithium secondary batteries Li ₄ Ti ₅ O ₁₂ which can be used as a material can be efficiently synthesized.

Claims (12)

Mixing a lithium salt powder containing lithium oxide and a titanium oxide powder (step 1); Calcining the mixed powder obtained in step 1 at a temperature equal to or higher than the melting point of the lithium salt (step 2); And Method for producing a lithium titanate spinel powder using a lithium-based molten salt, characterized in that it comprises a step (step 3) of washing and drying the powder produced in step 2. The method according to claim 1, wherein the lithium salt of step 1 is a lithium salt that can dissolve lithium oxide at 850 ° C. or less. The method for producing lithium titanate spinel powder using a lithium molten salt according to claim 1 or 2, wherein the lithium salt is lithium chloride. The method of claim 1, wherein the amount of lithium oxide contained in the lithium salt of step 1 is in the range of solubility in the lithium salt. The method of claim 4, wherein the lithium oxide is lithium chloride, and the content of the lithium oxide is 0.136 mol to 0.19 mol based on 1 mol of lithium chloride. The method of claim 1, wherein the mixing ratio of the lithium salt powder and the titanium oxide powder of step 1 is 1: 1.3 to 1: 4.0 of the molten salt of titanium and lithium of the lithium titanate spinel powder using a lithium molten salt Manufacturing method. The method of claim 6, wherein the mixing ratio is 1: 1.5 to 1: 2.0 in the molar ratio of the lithium titanate spinel powder manufacturing method using a lithium-based molten salt. The method of claim 1, wherein the calcination of step 2 is carried out at a temperature range of 650 ℃ to 850 ℃ a method for producing lithium titanate spinel powder using a lithium-based molten salt. The method of claim 8, wherein the firing temperature is 700 ℃ to 750 ℃ manufacturing method of lithium titanate spinel powder using a lithium-based molten salt. The method of claim 1, wherein the baking of step 2 is performed for 0.5 hours to 6 hours, the method for producing lithium titanate spinel powder using a lithium-based molten salt. The method for preparing lithium titanate spinel powder using a lithium-based molten salt according to claim 10, wherein the firing time is 0.5 to 2 hours. The method of claim 1, wherein the step 3 is washed with pure water, but the method until the washing solution is neutral, and then dried until the lithium titanate spinner powder using a lithium-based molten salt.

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