JP2015042611A - Method of producing lithium titanate compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a lithium titanate compound having a high lithium content.SOLUTION: An aqueous titanium-containing slurry is prepared and mixed with a lithium compound, the obtained mixture is agitated at a specific temperature for specific time and thus reacted into lithium titanate, and the obtained crystalline lithium titanate compound is dried.

Description

  The present invention relates to a method for producing an alkali metal titanate. In particular, the present invention relates to lithium titanate products having high Li: Ti molar ratios and their use.

  Various lithium titanates and their properties have been extensively studied due to the potential use of materials in battery applications. Lithium titanate has been used as an anode electrode material because it provides a high energy density to the battery and allows the battery to be charged. Lithium batteries are typically used in consumer electronics and entertainment electronics such as computers, cell phones and cameras.

The lithium ions in the lithium titanate are located in the TiO ₂ crystal lattice and most easily form the Li _x TiO ₂ form of the octahedral anatase structure. The goal is to get as many lithium ions as possible into this structure, but their number is limited by repulsive Coulomb interactions between lithium ions in the structure. The maximum amount of Li in TiO ₂ anatase type crystals is shown to be x = 0.5-1 depending on temperature and synthesis method.

Lithium titanate has heretofore been produced in various ways, particularly by solid state reactions performed at high temperatures of 200 ° C. to 1000 ° C. Typically, the product thus obtained consists of tetralithium titanate Li ₄ Ti ₅ O ₁₂ . In addition, various titanates having a Li: Ti ratio, for example, various Li _x Ti _y O ₄ structures in which x: y takes various values from 0.5 to 2, and, for example, Li ₄ TiO ₄ structures and Li ₂ Ti ₃ O ₇ structure and _Li x _Ti y _{O 12} is x = 3 to 5 and y = 4 to 6, and _Li 2 TiO ₃ is manufactured. It is known that the usefulness of materials in battery or storage battery applications decreases if the ratio of lithium to titanium increases to 2 as in the Li ₂ TiO ₃ structure. This is due to the fact that after the first discharge of the battery, oxides are generated and Li ions can no longer return. Instead, a LiTiO ₂ type structure with an O ₃ level that allows lithium migration is functional, but its Li: Ti ratio has been confirmed to remain low. Other possible lithium titanate structures are disclosed, for example, in the publication of Non-Patent Document 1.

In the paper of Non-Patent Document 2, nanocrystalline LiTiO ₂ is synthesized by a hydrothermal process. In this process, LiOH.H ₂ O was dissolved in ion exchange water and the solution was mixed with TiO ₂ powder (Degussa P25). The mixture was placed in an autoclave and heated at 180 ° C. and the corresponding pressure for 24 hours, then cooled in air, filtered and washed with water and acetone. In this method, cubic LiTiO ₂ was obtained, so that its lattice constant was 4.14 、 and its average crystal diameter was about 30 nm. The Li: Ti ratio of the product obtained in this way is a maximum of 1, so the Li content remains relatively low. This process cannot be used to freely adjust the crystal size of the product produced. Furthermore, production conditions such as high temperature and high pressure are not the best in terms of safety when operating in an industrial environment.

The paper of Non-Patent Document 3 describes the effect of particle size on the insertion of lithium into a TiO ₂ anatase type single crystal. In this study, TiO ₂ powder is dispersed in hexane and n-butyllithium is added to the mixture with slow stirring. After stirring for 3 days, the mixture was filtered, washed with hexane and dried. All production steps were performed in an argon cabinet. In this way, Li _x TiO ₂ with x = 0, 0.12, 0.4 or 0.8 was obtained. Furthermore, it has been observed that the amount of lithium can be increased with decreasing crystal diameter. When the crystal diameter was the smallest, 7 nm, the maximum amount of lithium led to the TiO ₂ crystal structure, whereby the composition corresponded to the formula Li ₁ TiO ₂ and the crystal structure had tetragonal I41 / amd symmetry. . In the product according to this description, the amount of Li remains low and it is not easy to implement this production condition industrially.

Patent Document 1, it is possible to adjust the particle size 5Nm～2000nm, and its BET discloses the preparation of titanium tetracalcium lithium _{(Li 4} Ti _{5 O 12)} is a ^{1m 2} / ^g~400m 2 / g doing. In this manufacturing method, a mixture containing a titanium compound and a lithium compound is formed. The mixture is evaporated to form a mixture of titanium compound and lithium compound. Evaporation is by spray drying the mixture at a temperature above the boiling point of the solvent of the mixture, preferably water, i.e. above 100 ° C. but below the temperature at which the reaction between the lithium compound and the titanium compound essentially occurs. Done. The titanium compound may be titanium oxychloride or an amorphous titanium oxide compound such as titanium chloride or titanium dioxide according to the examples. The lithium compound may be lithium chloride, lithium oxychloride, lithium nitrate, lithium hydroxide, or a mixture thereof. When the mixture obtained by evaporation is calcined, the reaction between lithium and titanium occurs and forms a lithium titanate product.

  The abstract of Patent Document 2 describes production of elongated lithium titanate particles having a laminated structure from titanic acid and a lithium compound using an aqueous solution having an ammonium compound at a temperature of 50 ° C. The presence of ammonia has the desired effect on the form of the precipitated compound, but ammonia easily causes technical problems in the process if it evaporates immediately as ammonia as the pH rises above 7. The nitrogen contained in the use solution constitutes an environmental problem in further processing.

European Patent No. 1409409 JP-A-9-309727 (WPINDEX AN: 1998-071742 [07]) European Patent No. 444798

ICDD 1998, ISSN 1084-3116, Powder Diffraction File, Release 1998: Datasets 1-48 plus 70-85 Zhang, D. et al., J. Ind. Eng. Chem., Vol. 13, No. 1, 2007 p. 92-96 Wagemaker, M. et al. J. Am. Chem. Soc. 2007, 129, 4323-4327

  An object of the present invention is to disclose a lithium titanate product having a high lithium content.

  Another object of the present invention is to provide a low temperature process for the production of alkali metal titanates on an industrial scale, in particular for the production of the lithium titanate product.

  In a first aspect of the invention, a lithium titanate product is provided. In a second aspect of the invention, a method for producing an alkali metal titanate is disclosed. In a third aspect of the present invention, a lithium battery is provided.

  Surprisingly, the inventors of the present invention use an aqueous titanium-containing slurry produced in the production of titanium dioxide to produce a slurry having titanium and an alkali metal compound such as lithium hydroxide at a temperature of less than 100 ° C. It was confirmed that when reacted, an alkali metal titanate product such as lithium titanate containing a large number of alkali metals such as lithium can be obtained at a low temperature by a simple and effective method.

  The present invention enables the production of new products having a high lithium content. This product is particularly suitable for electrical energy storage applications such as batteries, where the high content of lithium acting as a charge carrier is directly proportional to the ability of the battery to charge electrical energy. Furthermore, the method according to the invention is suitable for industrial scale and uses as safe and simple processing conditions and raw materials as possible. This method also does not require the use of high temperatures and / or high pressures and allows the production of products with low production energy.

When the formula is in the form of Li _x Ti _y O _z and y is 1, the molar ratio x: y is 1.1 to 1.8 and at the same time the molar ratio z: y is 2.0 to 4.5. FIG. 5 is a powder X-ray diffractogram of a lithium titanate product according to the present invention in a 2θ angle range of 10 ° to 135 °. Diagram showing powder X-ray diffractogram of a lithium titanate product (dried at 150 ° C. for A and dried at 200 ° C. for B) having the formula Li _x Ti _y O _z with a molar ratio x: y of 1.5 It is. Lithium titanate product having the formula Li _x Ti _y O _z with a molar ratio x: y of 1.42 and at the same time a z: y molar ratio in the sample of 3.4 (reacted at 25 ° C. for A, for B It is a figure which shows the powder X-ray diffractogram of (reaction at 60 degreeC). FIG. 5 shows a powder X-ray diffractogram of a product prepared at room temperature and having a Li: Ti ratio of 0.82. FIG. 5 shows a powder X-ray diffractogram of a product prepared at a temperature of 60 ° C. and having a Li: Ti ratio of 0.82. FIG. 5 shows a powder X-ray diffractogram of a product prepared at room temperature and having a Li: Ti ratio of 2.0. FIG. 4 shows a powder X-ray diffractogram of a product prepared at a temperature of 60 ° C. and having a Li: Ti ratio of 2.0. FIG. 2 shows a powder X-ray diffractogram of a product having a Li: Ti ratio of 1.5 (A prepared for 40 minutes at 50 ° C., B prepared for 90 minutes at 60 ° C.). Is a graph illustrating a powder X-ray diffractogram of Na _x Ti _y O _z compounds. It is a figure which shows the powder X-ray diffractogram of a product (A is dried at room temperature and B is dried at 60 degreeC). It is a figure which shows the influence of the calcination temperature with respect to the crystal diameter of a product.

According to the first aspect, the present invention provides that when y is 1, the molar ratio x: y is 1.1 to 1.8, and the z: y molar ratio is 2.0 to 4 at the same time. The lithium titanate product represented by Li _x Ti _y O _z is .5. When y is 1, the x: y molar ratio is preferably 1.3 to 1.8, and the x: y molar ratio is most preferably 1.3 to 1.7. Accordingly, with respect to the oxygen-titanium ratio, the z: y molar ratio is preferably 3.0 to 4.0, more preferably 3.1 to 3.9.

  The molar ratio can be determined, for example, by measuring the Li content and the Ti content with an ICP-OES analyzer such as Optima 4300DV from PerkinElmer, and then quantifying the amount of oxygen for the annealed sample based on weighing. It can be determined by any known method. The annealing loss is obtained as follows. Moisture is determined by weighing a known amount of sample dried to constant weight at 110 ± 3 ° C. The moisture content of the sample is calculated from the material loss. A known amount of sample is annealed at 1000 ± 30 ° C. The annealing loss of the sample is calculated from the material loss by checking the moisture part. The molar ratio of the product can be adjusted by the interrelationship between the reagents used in the production.

  According to a preferred embodiment, the crystal diameter of the lithium titanate according to the above formula is 15 nm to 40 nm, preferably 20 nm to 30 nm.

According to another preferred embodiment, the specific surface area of the product obtained (BET) ^{is, 10m 2 / g~200m 2 / g} , preferably ^{25m 2} / ^g~140m 2 / g, more preferably ^{25 m} 2 / g ˜100 m ² / g.

  Depending on the production conditions, for example, a cubic or tetragonal mixed crystal structure can be obtained. In order to achieve a pure tetragonal crystal structure, the resulting lithium titanate must be heat treated.

  The lithium titanate product is very pure and contains only a small amount of impurities. As impurities, typically less than 0.5 wt%, preferably less than 0.2 wt%, most preferably less than 0.15 wt% sodium, typically less than 0.12 wt%, preferably 0.05 There may be mentioned no more than wt% sulfur, more preferably no more than 0.01 wt% sulfur and typically no more than 0.01 wt% chlorine.

  According to a preferred embodiment, based on powder X-ray diffraction measurements (XRD), a reflection peak derived from a source material such as titanium dioxide, which would prove that some source material still remains, It can be stated that it is not observed from the final product produced. Thus, the reaction to lithium titanate appears to be complete. It is considered preferable that the reflection caused by the anatase type titanium oxide or the rutile type titanium dioxide is not observed from the XRD measurement result. Thus, it can be concluded that the amount of anatase or rutile titanium dioxide is at least less than 5% by weight, preferably less than 1% by weight.

  For powder X-ray diffraction, the lithium titanate product according to the invention is preferably reflected at angles of about 43.7 °, 63.4 °, 80.1 °, 96.1 ° and 112.9 ° (2θ). The variation in the measurement accuracy depending on the processing of the sample before the measurement, the crystallinity of the sample and the performance of the measuring instrument is ± 0.5 °. The relative intensities of the peaks are preferably about 100%, 40%, 15%, 5% and 10%, respectively. The powder X-ray diffractogram uses a Cu tube (Cu Kα), 40 kV / 40 mA, a measurement interval of 0.02 ° and a time per measurement of 1.0 seconds in a 2θ angle range of 10 ° to 135 °. Is required. Furthermore, the powder X-ray diffractogram according to FIG. 1 is preferably obtained from the lithium titanate product according to the invention.

According to a preferred embodiment, the lithium titanate product according to the invention has a volume distribution d ₅₀ with a particle size measurement of 15 μm or less, where d ₅₀ is, as is known, 50% of the particles of the volume distribution. It means having a diameter smaller than the numerical value.

  The lithium titanate product according to the invention is preferably prepared from an aqueous solution by low temperature synthesis, preferably below 100 ° C., at normal pressure and in standard atmosphere. The conditions and chemicals used are particularly suitable for industrial production and do not require exceptional prior measures such as inert protective gases when processing them.

In the method according to the second aspect of the present invention, the alkali metal titanate is prepared through the following steps (i) to (iv):
(I) preparing a titanium-containing aqueous slurry;
(Ii) mixing alkali metal compounds, thereby forming a mixture; and
(Iii) reacting the mixture thus produced to an alkali metal titanate at a temperature of 20 ° C. to 100 ° C. by stirring it at atmospheric pressure for up to 20 hours; and (iv) thereafter Drying the alkali metal titanate product thus obtained.

  In the process according to the present invention, while the slurry and the alkali metal compound are in contact with each other for a sufficiently long time, it reacts with the alkali metal compound to form an alkali metal titanate, preferably water acts as a solvent. An aqueous slurry, such as a slurry of a titanium compound, is prepared. Mixing is preferably such that the dispersion thus produced remains homogeneous and no settling occurs. The mixing speed can be, for example, 20 rpm to 200 rpm depending on the reactor size and mixer used. It is important that the mixing be sufficiently good so that the reaction is as complete as possible. In other respects, the mixing method is not critical.

  The reaction solvent is preferably water. Water is essentially derived from the slurry of titanium compound. As the solvent, an alcohol solution may be used, or an additive that improves the solubility of the starting material, for example, may be used in the solvent.

The alkali metal compound can be formed by a single alkali metal, or it can be a mixture or compound of several alkali metal compounds. The alkali metal compound is preferably a soluble lithium compound such as a lithium salt. However, many salts have detrimental effects in the form of impurities such as sulfate residues, nitrogen residues or chloride residues. The lithium compound is more preferably lithium hydroxide or lithium carbonate. The lithium compound is most preferably lithium hydroxide such as LiOH.H ₂ O, which has a reasonable price and sufficient reactivity.

  According to one embodiment, the alkali metal compound is added in step (ii) at an alkali metal (Me) -titanium (Ti) molar ratio approximately corresponding to the intended molar ratio of the final structure. Me: Ti is preferably 1.1 to 2.0, preferably 1.1 to 1.9, more preferably 1.3 to 1.8, most preferably 1.3 to 1.7, thus The intended molar ratio Me: Ti of the final product is about 1.5. If necessary, a solvent, preferably water, is further added to the mixture to facilitate stirring.

  According to a preferred embodiment, since the alkali metal compound is lithium hydroxide, the Li: Ti molar ratio of the lithium hydroxide and titanium-containing aqueous slurry to be mixed is 1.1 to 1.9, preferably 1.1. ~ 1.8, more preferably 1.3-1.8, most preferably 1.3-1.7, so that Li can be recovered as efficiently as possible in the structure, its intent The Li: Ti ratio is about 1.5.

  By maintaining the reaction temperature high in step (iii), the required reaction time is shortened. The mixture can be reacted to the alkali metal titanate at a temperature of less than 100 ° C, preferably up to 75 ° C, more preferably up to 65 ° C, and most preferably up to 55 ° C. The temperature may be close to room temperature, preferably at least 20 ° C., more preferably at least 30 ° C., and most preferably at least 40 ° C., so that any additional separate heating is not required and more energy is consumed. Small and production cost is reduced. The crystal diameter is also slightly reduced, for example, 15%.

  Depending on the amount of compound to be reacted, the quality, the mixture and the reaction temperature, reaction times shorter than 20 hours are sufficient, preferably up to 3 hours, more preferably up to 2 hours, most preferably up to 1 hour, for example up to 30 Minutes. Through suitable optimization of time and temperature, the operating range that is most energetically advantageous for the process is reached and production costs are reduced.

  According to one embodiment, the alkali metal compound, preferably lithium hydroxide, is added to the titanium-containing slurry in solid form, so that it dissolves in the slurry solvent, eg water. If necessary, an alkali metal compound such as lithium hydroxide may be first dissolved in water before being combined with the titanium-containing slurry.

  According to a preferred embodiment, the titanium-containing aqueous slurry of step (i) contains sodium titanate. The slurry more preferably consists essentially of sodium titanate.

  Sodium titanate can be prepared from various known titanium compounds such as titanium halides, titanium alcohols or organotitanium compounds by alkaline precipitation or by hydrolysis, but these titanium compounds are generally expensive and difficult to handle. Starting material, which in some cases can lead to impurities in the process.

According to one embodiment, sodium titanate is any known stable sodium titanate having properties that make it suitable for use under the conditions of the present invention. Sodium titanate is preferably represented by the formula Na _x Ti _y O _z . More preferably, x, y and z follow those shown in Table 1 as known.

  In powder X-ray diffraction measurements, sodium titanate according to the present invention is most preferred and characterized at angles of about 10 °, about 24 °, about 28 ° and about 48 ° (2θ), as shown in FIG. It was observed to have a reflection.

According to a preferred embodiment, sodium titanate is Na ₄ Ti ₉ O ₂₀ , Na ₄ Ti ₉ O ₂₀ .H ₂ O or Na _(4-x) H _x Ti ₉ O ₂₀ , where x is Na ion and The amount of dissolved OH ions is shown).

  According to another preferred embodiment, titanic acid is obtained from a titanium dioxide hydrate obtained by a sulfate process in the production of titanium dioxide by treating the titanium dioxide hydrate with an alkali into a sodium titanate slurry. Prepare sodium. From the ilmenite concentrate, the titanium dioxide hydrate is hydrolyzed with sulfuric acid, and this is submerged in water to a density of 300 g / l to 400 g / l to a titanium dioxide hydrate slurry, with a pH above 11. It is preferred to prepare sodium titanate by boiling with alkali to form a sodium titanate slurry, washing out the soluble sulfate and filtering. Most preferably, the sodium titanate is prepared by the method described in more detail in Applicant's US Pat.

  According to one embodiment, sodium titanate is hydrated in water, depending on the particle size and / or shape of the indicated sodium titanate, 100 g / l to 800 g / l, more preferably 100 g / l to 600 g. / L, most preferably 150 g / l to 450 g / l, e.g. 150 g / l to 350 g / l.

  According to another embodiment, the titanium-containing aqueous slurry of step (i) is prepared by a sulfate process in the production of titanium dioxide, preferably from titanyl sulfate obtained by alkaline precipitation or hydrolysis. Thermal hydrolysis of ilmenite concentrate from ilmenite concentrate to titanium dioxide hydrate using sulfuric acid in a sulfate process in the production of titanium dioxide, which is hydrated in water and has a density of 300 g / l to 400 g / l. It is more preferable to prepare the titanium-containing aqueous slurry of step (i) from titanyl sulfate obtained by making a titanium hydrate slurry. The titanium-containing aqueous slurry of step (i) is a titanium dioxide hydrate as described above in the manner described in the applicant's earlier patent document 3 (incorporated herein by reference). Most preferably, it is prepared from a slurry.

  From the dried product obtained in step (iv), as described above, the crystal structure and crystal diameter, as well as the specific surface area, particle diameter and particle size distribution, and most important such as Li and Ti by X-ray diffraction. Chemical analysis for components and impurities such as Na, S and Cl can be measured. A large particle size is advantageous in terms of workability because in that case there is less dust formation. Depending on the application, it may be necessary to coat with a material, so for example a small particle size is preferred.

  According to a preferred embodiment, the finished titanate product is dried at an elevated temperature, preferably at a temperature of less than 250 ° C., more preferably less than 200 ° C., most preferably less than 155 ° C., such as 110 ° C. or less. For drying, use known equipment known in the art and most suitable for the individual scale and production capacity, for example reel oven, spray drying, vacuum drying, vertical drying oven or rotary drying oven .

The dried alkali metal titanate product obtained by the above process is preferably at a temperature of 350 ° C. to 1050 ° C., more preferably at a temperature of 500 ° C. to 1050 ° C., most preferably 700 ° C. to 900 ° C., For example, it is further processed by heat treatment at a temperature of 700 ° C. to 800 ° C. to change its crystal structure. The titanate obtained before heat treatment, preferably lithium titanate, is essentially cubic, or partly cubic and partly different crystalline forms depending on the production conditions. During the heat treatment, the crystal diameter may change essentially to another form, such as a tetragonal form. When heat treating the titanate product, the titanate product preferably changes to spinel tetralithium titanate (Li ₄ Ti ₅ O ₁₂ ) at a temperature of 700 ° C. to 800 ° C., and this treatment time is More than 1 hour, preferably 1.5 hours or more.

  The present invention also discloses a lithium titanate product produced by the above method.

According to a third aspect of the present invention there is provided a lithium battery containing any of the products according to the above description. The product thus obtained has the advantage of a high Li: Ti ratio over that of the LiTiO ₂ structure and it has been found that such a product is active. However, it was found to be inactive if the ratio remained below 2 as in the Li ₂ TiO ₃ structure.

  Hereinafter, the present invention will be described in more detail with reference to examples. The purpose of the examples is not to limit the invention.

  The Li: Ti ratio shown in the examples is determined by accurately weighing a 100 g sample to be evaluated in a Teflon container and adding 10 ml of analytical quality concentrated hydrofluoric acid. Obtained by the prior art method. Heat the container in a sand bath until the sample is dissolved. The cooled solution is diluted to 50 ml with deionized water. For measurement, the sample is diluted 1:20 with 10% analytical quality hydrochloric acid.

  The lithium and titanium concentrations of the samples thus prepared were 670.784 nm, 610.362 nm and 460.308 nm for lithium and 334.945 nm for titanium using an Optima 4300 DV ICP-OES analyzer from PerkinElmer. It is determined at emission wavelengths of 336.125 nm and 337.282 nm.

  The particle size of the particles produced can be determined using applicable equipment, such as a Mastersizer 2000 device from Malvern. The specific surface area may be determined using any apparatus known in the art, for example, a NOVA 3200 (version 6.11) apparatus manufactured by Quantachrome Corp. used in the following measurement.

[Example 1]
The production of titanium dioxide by the sulfate process begins by reacting the ilmenite concentrate with sulfuric acid. The resulting solid reaction cake is dissolved with water and spent acid. Impurities are removed and iron sulfate is crystallized. The titanium-containing solution is concentrated and titanium dioxide hydrate is precipitated by hydrolysis. This precipitated material is washed in several steps to be free of salt.

About 10 tons of washed titanium dioxide hydrate precipitated material, expressed as TiO ₂ , is watered to a density of 300 g / l to 400 g / l in water. The target is 350 g / l. The slurry thus produced is made strongly alkaline (pH> 11) by adding about 15 tons of NaOH in the form of a 700 g / l NaOH solution at 60 ° C. The temperature of the slurry is raised to 95 ° C. and the slurry is stirred at this temperature for 2 hours. During the process, the titanium dioxide hydrate material reacts with the alkaline liquid to form solid sodium titanate, and the slurry is washed with hot water for a long time until no sulfate is found in the filtrate due to barium chloride precipitation, Remove sulfate ions from solid sodium titanate.

  The filtrate cake having sodium free from sulfate is poured into water so as to have a slurry concentration of about 200 g / l in terms of titanium dioxide and heated at 60 ° C. under continuous stirring. Thereafter, the pH of the slurry is adjusted to a target value of 6 by adding concentrated hydrochloric acid (20 wt%). The slurry is treated for 120 minutes at 60 ° C. under continuous stirring. The pH is maintained at 6 during processing. The precipitate is filtered and washed with warm water.

The obtained precipitate is re-watered in water so that the concentration of the slurry is about 300 g / l in terms of titanium dioxide. Solid lithium hydroxide (LiOH.H ₂ O) is added to the slurry at 38.4 g per 50 g TiO ₂ , corresponding to a Li / Ti molar ratio of 1.5. Add water as needed to facilitate mixing. The slurry is heated to 50 ° C. and treated at this temperature for 40 minutes under continuous stirring. The slurry is divided into two parts, one part is dried at 150 ° C. for 120 minutes in a vertical drying oven and the other part is dried at 200 ° C. in the corresponding environment.

  The crystal form and diameter of the dry powder are determined in a 2θ angle range of 10 ° to 70 ° using a Philips XRD apparatus. According to X-ray diffraction analysis, the desired crystalline lithium titanate having an average crystal size of about 25 nm is formed for both samples and the effect of drying temperature is not seen. There are no peaks characteristic of the anatase type in FIG. 2A (150 ° C.) or FIG. 2B (200 ° C.).

  Samples dried at 200 ° C. are further processed by washing with a large amount of water and drying at 105 ° C. until dry. Particle size and specific surface area are determined for unwashed samples, Li concentration, Ti concentration, S concentration and Cl concentration, and powder X-ray diffractogram and specific surface area for washed samples (Table 2).

Table 2

  As shown by the examples, the product is produced at a low temperature of about 50 ° C. using a short reaction time and sodium titanate as starting material.

[Example 2]
Lithium titanate is divided into two parts after the addition of lithium hydroxide, the first part is stirred overnight at room temperature (about 20 hours), and the second part is placed in a 60 ° C. water bath. In the manner described in Example 1 except that the mixture is stirred overnight. Both samples are dried at 200 ° C. for 120 minutes in a rotary drying oven.

As in Example 1, X-ray diffraction analysis demonstrates the formation of crystalline lithium titanate having an average crystal size of about 25 nm in both samples. There are no peaks characteristic of the anatase type in the diagram. According to chemical analysis, these Li _x Ti _y O _z samples have Li: Ti molar ratios of 1.42 and 1.39, respectively, and the z: y molar ratio in both samples is 3.5. . The diffractogram for the product is shown in FIG. 3A (25 ° C.) and FIG. 3B (60 ° C.).

  The sample reacted at 60 ° C. is further processed by washing with a large amount of water and drying at 105 ° C. until dry. Particle size and specific surface area are determined for unwashed samples, Li concentration, Ti concentration, S concentration and Cl concentration, as well as powder X-ray diffractogram and specific surface area for washed samples (Table 3).

Table 3

  The product reacted at room temperature and the product reacted at 60 ° C. showed the same powder X-ray diffractogram. Increasing temperature did not improve compound formation. Longer processing times were observed to slightly reduce the size of the lithium titanate crystals. The powder X-ray diffractogram gives a crystal diameter of 22 nm. Anatase-type peaks are not seen in the diagram. This example shows that the reaction with sodium titanate is achieved at temperatures as low as 25 ° C.

[Example 3]
Wash the washed titanium dioxide hydrate material from Example 1 in water so that the slurry concentration is about 300 g / l in terms of titanium dioxide. The slurry is heated to 60 ° C. and the pH is adjusted to 6.4 with sodium hydroxide. The slurry is treated for 120 minutes at 60 ° C. under continuous stirring. The pH is maintained constant (6.4) during processing. The precipitate is filtered and washed with a large amount of hot water. The cake obtained is dried in a small amount at 105 ° C. According to analysis, the dried cake had a sodium concentration of 68 mg / kg and a sulfur concentration of 0.11% by weight.

The remaining cake is rewatered to a density of about 300 g / l in water. Divide the slurry into four parts (Sample 1 to Sample 4). Solid lithium hydroxide (LiOH.H ₂ O) is added to each portion and they are treated according to Table 4.

Table 4

  The sample is filtered and the resulting cake is further divided into two parts, one part being washed with a large amount of water and dried at 200 ° C. The other part is dried at the same temperature (non-washing). X-ray diffractograms of all sample powders are obtained in a 2θ angle range of 10 ° to 70 °. In addition, the specific surface area, particle size, chemical analysis of component Li, component Ti and component Na, and SEM and TEM images of the washed and dried sample powder are determined.

The specific surface area is found to be 123 m ² / g (NOVA 3200 High Speed Gas Sorption Analyzer (Quantachrome Corp.)).

Particle size distribution parameters: d ₅₀ = 1.5 μm, d ₁₀ = 0.8 μm and d ₉₀ = 2.7 μm

  Chemical analysis yield Li 9.1 wt%, Ti 43.7 wt% and Na less than 1.0 wt%, Li / Ti = 1.42

  According to X-ray diffraction analysis, the crystal form was as shown in Table 5.

Table 5

  This example shows that the reaction is also achieved using a titanium dioxide hydrate material, but this requires a slightly higher reaction temperature than the previous examples.

[Example 4]
The washed titanium dioxide hydrate material described in Example 1 is soaked in water so that the concentration of the slurry is about 300 g / l in terms of titanium dioxide. The slurry is heated to 60 ° C. and the pH is adjusted to 6.4 with sodium hydroxide. The slurry is stirred at 60 ° C. for 120 minutes. The pH is maintained constant (6.4) during processing. The precipitate is filtered and washed with a large amount of hot water. The filtrate cake is dried at 105 ° C. for a small amount for analysis. According to analysis, the dried cake had a sodium concentration of 91 mg / kg and a sulfur concentration of 0.081% by weight.

  The remaining cake is rewatered in water to a density of 300 g / l. The resulting slurry is divided into two parts.

Solid lithium hydroxide (LiOH.H ₂ O) is added to the first part at 39.4 g (Li / Ti molar ratio 1.5) per 50 g TiO ₂ . The slurry thus produced is stirred at 50 ° C. for 40 minutes. The slurry is dried at 200 ° C. in a vertical furnace.

Solid lithium hydroxide (LiOH.H ₂ O) is added to the second portion at 52.5 g (Li / Ti molar ratio 2.0) per 50 g TiO ₂ . The slurry thus produced is stirred at 60 ° C. for 90 minutes. The slurry is dried at 200 ° C. in a vertical furnace.

The powder X-ray diffractogram is measured on the dry powder in the 2θ angle range of 10 ° to 70 °. According to X-ray diffraction analysis, only the LiTiO ₂ crystal form is evident in both samples (FIG. 8A (1.5) and FIG. 8B (2.0)).

  These samples dried at 200 ° C. are washed with more water and re-dried at 105 ° C. The washed, dried powder is analyzed for Li content, Ti content and Na content. The results are shown in Table 6.

Table 6

[Example 5]
Lithium titanate was prepared by adding solid lithium hydroxide (LiOH.H ₂ O) to a neutralized and washed titanium dioxide hydrate material at a Li / Ti molar ratio of 1.5, and adding the resulting mixture to 50 Produced according to Example 1 except stirring for 90 minutes at 0C.

  The product part is dried at 60 ° C. and normal pressure without washing, and the other part is dried in vacuum at 25 ° C.

  XRD is measured for both products after drying (FIGS. 10A and 10B). The X-ray diffractogram shows that some starting material still remains in the sample dried at room temperature, and the sample dried at 60 ° C. contains little starting material.

  The sample dried at 60 ° C. is divided into four parts and then calcined at 200 ° C., 300 ° C., 400 ° C. and 500 ° C. for 90 minutes. Next, measurement is performed on samples obtained by calcining XRD (FIGS. 11A to 11D, respectively). From the X-ray diffractogram it can be seen that the sample has a reflection characteristic of cubic lithium titanate according to the invention. In addition, initial changes in the crystal structure are evident at higher temperatures.

Claims (17)

A method for producing a lithium titanate compound comprising:
(I) preparing a titanium-containing aqueous slurry;
(Ii) mixing a lithium compound with the titanium-containing aqueous slurry to form a mixture; and
(Iii) reacting the resulting mixture to lithium titanate by stirring at a temperature of 20 ° C. to 100 ° C. at normal pressure for a maximum of 20 hours; and (iv ) the obtained crystalline lithium titanate compound. Drying step,
A method characterized by comprising:   The process according to claim 1, characterized in that the mixture is reacted to lithium titanate in the step (iii) at a temperature of up to 75 ° C.   The process according to claim 1 or 2, characterized in that the mixture is reacted in the step (iii) to lithium titanate at a temperature of a minimum of 30 ° C.   The method according to any one of claims 1 to 3, wherein in the step (ii), lithium hydroxide is added to the titanium-containing aqueous slurry in a solid form.   5. A process according to any one of the preceding claims, characterized in that the mixture is reacted in the step (iii) with lithium titanate for a maximum of 3 hours.   The method according to any one of claims 1 to 5, characterized in that the titanium-containing aqueous slurry of step (i) contains sodium titanate. By the sodium titanate slurry treated titanium dioxide hydrate obtained by sulphate process in the production of titanium dioxide with an alkali, characterized by preparing the sodium titanate of claim 6 Method.   From the ilmenite concentrate, the titanium dioxide hydrate is hydrolyzed with sulfuric acid, and this is submerged in water to a density of 300 g / l to 400 g / l to a titanium dioxide hydrate slurry, with a pH above 11. 8. The method of claim 7, wherein the sodium titanate is prepared by boiling with an alkali to form a sodium titanate slurry, washing out the soluble sulfate and filtering. The method according to claim 7 or 8, wherein the sodium titanate is hydrated in water to form a slurry having a density of 100 g / l to 800 g / l.   The method according to any one of claims 1 to 5, characterized in that the titanium-containing aqueous slurry of step (i) is prepared from titanyl chloride obtained by a sulfate process in the production of titanium dioxide.   Thermal hydrolysis of ilmenite concentrate from ilmenite concentrate to titanium dioxide hydrate using sulfuric acid in a sulfate process in the production of titanium dioxide, which is hydrated in water and has a density of 300 g / l to 400 g / l. 11. The titanium-containing aqueous slurry of the step (i) is prepared from titanyl chloride obtained by making a titanium hydrate slurry, according to any one of claims 1 to 5 and 10. Method. The method according to any one of claims 3 to 11, wherein the lithium titanate compound obtained in the step (iv) is dried at less than 250 ° C. Wherein the dried lithium titanate compound was further, 5 00 ° C. to the heat treatment at a temperature of to 1050 ° C., characterized by the crystal structure to a tetragonal, according to any one of claims 1 to 12 the method of.   14. The lithium hydroxide according to claim 1, wherein the lithium: Ti molar ratio of the lithium hydroxide and the titanium-containing aqueous slurry to be mixed is 1.1 to 2.0. Method. It is manufactured by the method according to any one of claims 1 to 14, and Li _x Ti _y O _z A lithium titanate compound having the formula:
x: y molar ratio is 1.1-1.8, z: y molar ratio is 2.0-4.5,
The crystal diameter is 15 nm to 40 nm,
Specific surface area (BET) is 10m ² / G-200m ² / G, and
Particle size distribution d ₅₀ Is 15 μm or less,
The lithium titanate compound characterized by the above-mentioned. The titanic acid according to claim 15, wherein the reflection in powder X-ray diffraction is at angles of 43.7 °, 63.4 °, 80.1 °, 96.1 ° and 112.9 ° (2θ). Lithium compound. A lithium battery comprising the lithium titanate compound according to claim 15 .

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