JPH09309727A - Lithium titanate, its production and lithium battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain lithium titanate having many voids and controlled in particle size and shape by heating and dehydrating lithium titanate hydrate obtained by reacting a titanic acid compound with a lithium compound in water. SOLUTION: A titanium compound is reacted with an ammonium compound in water at 0-50 deg.C to afford a titanic acid compound. The titanic acid compound is reacted with a lithium compound at >=50 deg.C, as necessary, in water containing 0.01-5mol/L ammonium compound to provide lithium titanate hydrate. The lithium titanate hydrate is dried at 30-200 deg.C and heated at 200-800 deg.C and dehydrated to provide the lithium titanate having a laminate structure, 1-300m<2> /g specific surface area and 0.1-50μm longest particle diameter and having voids in particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to lithium titanate, which is a compound useful as a negative electrode material for lithium batteries, a method for producing the same, and a lithium battery using the same.

[0002]

2. Description of the Related Art Lithium titanate has the general formula Li _X Ti _Y.
A compound represented by O ₄ , and a typical compound is L
i _2.67 Ti _1.33 O ₄ , LiTi ₂ O ₄ , Li _1.33 Ti
_1.67 O ₄ , Li _1.14 Ti _1.71 O _4, and the like. To obtain this lithium titanate, a method of heat-treating a mixture of titanium oxide and a lithium compound at a temperature of 700 to 1600 ° C. is used (see JP-A-6-275263).

[0003]

Since the lithium titanate obtained by the above-mentioned prior art method is a sintered body in which sintering between particles has occurred unevenly, the size and shape of the particles cannot be controlled. There's a problem. Furthermore, since the reaction for obtaining lithium titanate is a solid-solid reaction between the titanium oxide powder and the lithium compound powder, the reactivity is poor even if heat treatment is performed at a high temperature, and there is also a problem that a large amount of raw material powder remains. On the other hand, a mixture of titanium oxide and a lithium compound
Even if it heat-processes at a low temperature of 00 degreeC or less, there exists a problem that reaction will not progress and lithium titanate cannot be obtained.

[0004]

As a result of various studies to obtain lithium titanate useful as a negative electrode material for lithium batteries, the present inventors have heated lithium titanate hydrate obtained by a specific method. It was found that lithium titanate having a large number of voids can be obtained by dehydration, and that lithium titanate in which the size and shape of particles are controlled, and the like were further studied, and the present invention was completed.

That is, the present invention is to provide lithium titanate having many voids in the particles, and further lithium titanate in which the size and shape of the particles are controlled. The present invention also provides a method for efficiently obtaining the lithium titanate. Further, the present invention provides
A negative electrode for a lithium battery using the above lithium titanate,
Further, it is to provide a lithium battery using the same.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The present invention has the general formula Li _X Ti _Y O
Relating to lithium titanate represented by ₄ ,
It may be a single phase of lithium titanate or a mixture of lithium titanate and titanium oxide. The values of X and Y in the above general formula are expressed by the value of X / Y, and the range of 0.5 to 2 is a value that gives a preferable composition. The lithium titanate of the present invention is characterized by having voids in its particles. If voids exist inside the lithium titanate particles,
The specific surface area is increased, and as a result, more substances and ions such as lithium can be captured, so that the characteristics of the negative electrode for lithium batteries and the like are excellent. The presence of the voids can be confirmed by measuring the void amount. If the void amount is 0.005 ml / g or more, it can be recognized that the particles have voids. The void volume is preferably in the range of 0.01 to 1.5 ml / g, and more preferably 0.01 to 0.7 ml / g because of its excellent properties when used as a negative electrode material of a lithium battery. Also,
The specific surface area is preferably in the range of 1 to 300 m ² / g, more preferably 5 to 300 m ² / g, and most preferably 10 to 300 m ² / g.

A preferable controlled particle shape of the lithium titanate of the present invention is a laminated structure, and a large amount of voids can be secured between the layers. The laminated structure refers to a structure in which two or more plate-shaped or flaky lithium titanate particles are stacked, and such a laminated structure can be confirmed by observation with an electron microscope.

Further, the preferable lithium titanate of the present invention is a fine particle whose size is controlled. The particle diameter (longest diameter) can be appropriately designed, but 0.1-50 μm is a preferable range because it has excellent characteristics when used as a negative electrode material of a lithium battery, and 0.2
˜30 μm is a more preferable range.

Next, the present invention is a method for producing lithium titanate, which comprises a step of reacting a titanium compound and an ammonium compound in water to obtain a titanic acid compound, wherein the titanic acid compound and the lithium compound are reacted in water. And a step of obtaining lithium titanate hydrate by heating and dehydrating the lithium titanate hydrate by heating.
First, the above-mentioned step is a step of obtaining a compound of titanic acid, and as the titanium compound used therefor, an inorganic titanium compound such as titanium sulfate, titanyl sulfate or titanium chloride, or an organic titanium compound such as titanium alkoxide can be used. In particular, titanium chloride is preferable because it can reduce the residual amount of impurities in lithium titanate. Further, as the ammonium compound, ammonia water, ammonium carbonate,
Ammonium sulfate, ammonium nitrate and the like can be used. When an alkali metal compound such as a sodium compound or a potassium compound is used in place of the ammonium compound, the elements of sodium and potassium remain in the obtained titanic acid compound, and inter-particle burning occurs in the subsequent dehydration by heating. It is not preferable because it causes binding and tends to make the size and shape of the particles non-uniform. The reaction proceeds by mixing the titanium compound and the ammonium compound in water, and orthotitanic acid (H ₄ TiO ₄ ) or H _{4 -n} (N ₄ N in which its hydrogen ion is replaced with ammonium ion)
H ₄₎ titanate compound is a compound represented by _n TiO ₄ can be obtained. The replacement amount of ammonium ions in H _4-n (NH ₄ ) _n TiO ₄ can be arbitrarily changed by adjusting conditions such as ammonium ion concentration, free hydroxyl group concentration, hydrogen ion concentration and reaction temperature during the reaction. Since the particle size of the obtained titanic acid compound affects the particle size of lithium titanate obtained in the subsequent step, if the reaction temperature is set in the range of 0 to 50 ° C., the fine particle titanate compound is obtained. Is more preferable, and fine particulate lithium titanate can be obtained. A more preferable temperature range is 5 to 40 ° C, and the most preferable temperature range is 10 to 30 ° C.

The titanic acid compound thus obtained may be filtered, washed, acid washed, or dried, if necessary.

The next step is a step of obtaining a lithium titanate hydrate by using the titanic acid compound obtained in the above step, which is a step of reacting the titanic acid compound and the lithium compound in water. is there. As the lithium compound, a water-soluble lithium compound such as lithium hydroxide, lithium carbonate, lithium nitrate, and lithium sulfate can be used. The reaction proceeds by mixing the lithium compound and the titanate compound in water. When the temperature of this reaction is 50 ° C. or higher, lithium titanate hydrate having excellent crystallinity can be obtained, which is preferable. A more preferred temperature range is 100 ° C. or higher, an even more preferred temperature range is 100 to 250 ° C., and a most preferred temperature range is 130 to 200 ° C. When the reaction is carried out at a temperature of 100 ° C. or higher, it is preferable that the lithium compound and the titanate compound are placed in an autoclave and subjected to hydrothermal treatment under a saturated vapor pressure or under a pressure. It is more preferable that the hydrothermal treatment be performed in the presence of an ammonium compound, since a lithium titanate hydrate having good crystallinity and a well-formed shape can be obtained even at a lower hydrothermal treatment temperature. Ammonia water, ammonia gas, ammonium carbonate, ammonium sulfate, ammonium nitrate and the like can be used as the ammonium compound present during the hydrothermal treatment. The amount of the ammonium compound to be present is about 0.01 to 5 mol / l,
It is preferably 0.1 to 3 mol / l. By such a hydrothermal treatment, a lithium titanate hydrate having a laminated structure can be obtained.

The lithium titanate hydrate thus obtained may be filtered and, if necessary, washed or dried. The drying temperature can be appropriately set as long as the temperature is lower than the temperature at which lithium titanate hydrate releases water of crystallization, and a temperature of about 30 to 200 ° C. is appropriate.

The next step is the step of heating and dehydrating the lithium titanate hydrate obtained in the above step to obtain lithium titanate. The temperature of the heat dehydration is from the temperature at which the lithium titanate hydrate releases the water of crystallization to the temperature at which the voids of the obtained lithium titanate disappear. It is considered that the temperature range of this heat dehydration may differ depending on the composition of the lithium titanate hydrate, the amount of crystal water, etc., but it is about 200 to 800 ° C., and in order to obtain lithium titanate with many voids. Then 2
The range of 50 to 700 ° C is preferable, and the range of 350 to 650 ° C is more preferable. Thus, the lithium titanate of the present invention is obtained.

Next, the present invention is a lithium battery negative electrode comprising the above-mentioned lithium titanate, and further a lithium battery comprising the negative electrode. The negative electrode for a lithium battery can be obtained by appropriately adding a conductive material such as carbon black and a binder such as a fluororesin to the lithium titanate of the present invention and molding the mixture. Further, a lithium battery includes the above-mentioned negative electrode, positive electrode, and electrolytic solution. For the positive electrode, a commonly used material such as lithium-containing manganese dioxide, lithium cobalt oxide, lithium nickel oxide, or vanadium pentoxide can be used. In addition, the electrolytic solution, propylene carbonate,
LiPF ₆ , LiClO ₄ , LiCF ₃ S in a solvent such as ethylene carbonate or 1,2-dimethoxyethane
A commonly used electrolytic solution such as one in which a lithium salt such as O ₃ , LiN (CF ₃ SO ₂ ) ₂ or LiBF ₄ is dissolved can be used. These materials can be combined to form a lithium battery.

[0015]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited to these examples.

Example 1 (1) Synthesis of titanic acid compound In a 5 l 4-neck flask, 28% by weight of ammonia water 91 was added.
1 ml and 1339 ml of pure water were added, and while stirring, ice-cooling was performed so that the temperature of the solution became 10 to 15 ° C., and 1.25
2250 ml of a mol / l titanium tetrachloride aqueous solution was added over 2 hours and then aged for 1 hour to obtain a precipitate. The pH after aging is 8.85 and the TiO ₂ concentration is 50 g / l.
And the free hydroxyl group concentration was 0.5 mol / l.

Next, an aqueous hydrochloric acid solution prepared by diluting 199 ml of 35% by weight hydrochloric acid with 300 ml of pure water was added to the above aged slurry over 1 hour to adjust the pH to 5.50, and then the pH was adjusted to 5.50. Aged for 1 hour while holding. Thereafter, the precipitate was filtered and washed to remove ammonia and chloride ions, and the obtained filter cake was repulped to T
A slurry having an iO ₂ concentration of 50 g / l was obtained. Then, while cooling with ice, 26 ml of 35% by weight hydrochloric acid was added to the slurry.
After adjusting the pH to 5.50 by adding a hydrochloric acid aqueous solution diluted with 104 ml of pure water over 1 hour, the mixture was aged for 1 hour while maintaining the pH, and then the precipitate was filtered and washed, A titanic acid compound was obtained.

A small amount of the titanic acid compound thus obtained was dried at a temperature of 50 ° C. and its physical properties were examined. As a result, this titanic acid compound was an aggregate of fine particles (amorphous form), and was amorphous in X-ray. According to the chemical analysis, the component ratio was 47.0% by weight of Ti, N
H ₄ 1.44 wt%, a Cl 0.07 wt%, the composition is estimated to H _3.92 (NH ₄₎ a _0.08 TiO _4. Further, DSC analysis revealed that the polymer was dehydrated at 111 ° C. and crystallized into anatase at 440 ° C.

(2) Synthesis of Lithium Titanate Hydrate The titanate compound obtained in (1) above is repulped to give T.
A slurry having an iO ₂ concentration of 55.02 g / l was obtained. The pH of this slurry was 6.90 and the conductivity was 330 μS /
cm. 3.64 l of this slurry was charged into a 5-l4 neck flask, and while cooling the ice with ice so that the temperature of the slurry was 10 to 15 ° C, an aqueous solution in which 84.97 g of lithium hydroxide monohydrate was dissolved in 360 ml of pure water was added. It was added over time and then aged for 1 hour. After completion of the addition, the pH of the slurry was 12.1, and the TiO ₂ concentration was 50 g / l. The added lithium compound is Li / Ti
The molar ratio was 0.8. Next, the slurry thus obtained was charged into an autoclave and hydrothermally treated at a temperature of 190 ° C. for 2 hours. The slurry after the hydrothermal treatment was thickened into a paste, had a pH of 13, and had an ammonia odor. Then, the hydrothermally treated slurry was filtered and then dried at a temperature of 50 ° C. without washing to obtain a lithium titanate hydrate.

The physical properties of the thus obtained lithium titanate hydrate were examined. As a result, the lithium titanate hydrate was fine particles having an ultrathin plate-like shape with a long diameter of 1 μm, a short diameter of 0.8 μm, and a thickness of about 16 nm as observed by an electron microscope, and had four layers in the thickness direction. It was found that the layers had a laminated structure with a certain degree of overlap, and the layer spacing was about 4 nm. Further, it was found from the diffraction pattern of X-ray diffraction that the crystallinity was excellent. Furthermore, according to the chemical analysis, the component ratios are Ti 45.6% by weight and Li 5.3.
7% by weight, NH ₄ <0.01% by weight, Cl <0.005
% By weight, and its composition is
It is estimated to be _1.33 Ti _1.67 O _{4 .H 2} O. Furthermore, according to the DSC analysis, the adhered water was desorbed at 75 ° C.
It was found that water of crystallization was released at 15 ° C., a phase transition was made to Li _1.33 Ti _1.67 O ₄ , and crystallization was carried out at 337 ° C.

(3) Synthesis of lithium titanate The lithium titanate hydrate obtained in (2) above was pulverized in an agate mortar, and then 15 g of the pulverized product was weighed into an alumina crucible, 250, 400, 500, 600. , Lithium titanate of the present invention (Samples A to E) was obtained by placing in an electric furnace set to a temperature of 700 ° C. and heating and dehydration in the atmosphere for 2 hours.

The physical properties of the samples A to E thus obtained were examined. As a result, the lithium titanate is a fine particle having an ultrathin plate-like shape with a long diameter of 1 μm, a short diameter of 0.8 μm, and a thickness of 10 to 50 nm as observed by an electron microscope, and has about 4 layers in the thickness direction. It was found to have an overlapping layered structure. It was found that the layer spacing was widest in the sample B heat-dehydrated at a temperature of 400 ° C., and in the sample heat-dehydrated at a temperature higher than 400 ° C., crystal growth and densification occurred and the layer spacing gradually narrowed. Then B
Table 1 shows the measurement results of the specific surface area by the ET method and the measurement results of the void amount by nitrogen adsorption. In addition, Bell Soap 28 manufactured by Nippon Bell Co., Ltd. was used for the measurement of the void amount. From this result, it was found that each of Samples A to E had voids in the particles. In addition, from the diffraction pattern of X-ray diffraction,
Samples A to E were Li _1.33 Ti _1.67 O ₄ , and as shown in Table 2, when the temperature of heat dehydration was raised, the interplanar spacing gradually became smaller, and the value of the interplanar spacing described in the ASTM card was obtained. Found to approach.

[0023]

[Table 1]

[0024]

[Table 2]

Example 2 (1) Synthesis of Titanic Acid Compound A titanic acid compound was obtained according to the method described in (1) of Example 1 above. (2) Synthesis of lithium titanate hydrate The titanate compound obtained in (1) above is repulped to give T
A slurry having an iO ₂ concentration of 56.24 g / l was obtained. 1.494 l of this slurry and 0.208 l of pure water were charged into a 3 l 4-neck flask, and an ice-cooled 3.075N lithium hydroxide aqueous solution was added over 1 hour while cooling the ice so that the temperature of the slurry was 10 to 15 ° C. Then, 0.376 l of pure water was added, and the mixture was stirred for 1 hour and aged. Next, the slurry thus obtained was charged into an autoclave and subjected to a hydrothermal treatment at a temperature of 170 ° C. for 4 hours. Next, the hydrothermally treated slurry was filtered and then dried at a temperature of 110 ° C. without washing to obtain a lithium titanate hydrate.

The physical properties of the thus obtained lithium titanate hydrate were examined. As a result, this lithium titanate hydrate had a major axis of 0.8 μm as observed by an electron microscope.
It was found that it had an extremely thin plate-like shape with m, a minor axis of 0.65 μm, and a thickness of about 20 nm. Specific surface area is 11
It was 9.2 m ² / g and the void volume was 0.408 ml / g. In addition, Bell Soap 28 manufactured by Nippon Bell Co., Ltd. was used for the measurement of the void amount. Further, it was found from the diffraction pattern of X-ray diffraction that the crystallinity was excellent. Further, according to the chemical analysis, the component ratios are as follows: Ti 43.1% by weight, Li 4.85% by weight, NH ₄ <0.01% by weight, C
l <0.005% by weight, and X-ray diffraction _{shows that} Li _1.33 T
The presence of i _1.67 O _{4 .H 2} O was confirmed. Furthermore, DS
According to C analysis, water of crystallization was released at 208 ° C. to give Li _1.33
It was found to undergo a phase transition to Ti _1.67 O ₄ and crystallize at 345 ° C.

(3) Synthesis of lithium titanate The lithium titanate hydrate obtained in (2) above was crushed in an agate mortar, and 15 g of the crushed product was weighed into an alumina crucible at 550, 590 and 630 ° C. The lithium titanate of the present invention (Samples F to H) was obtained by placing in an electric furnace set to each temperature and heating and dehydrating in the atmosphere for 2 hours.

The physical properties of the samples F to H thus obtained were examined. As a result, it was found by electron microscope observation that the lithium titanate was fine particles having a major axis of 0.2 to 0.3 μm and had an extremely thin plate shape. Next, Table 3 shows the measurement results of the specific surface area by the BET method and the measurement results of the void amount by nitrogen adsorption. In addition, Bell Soap 28 manufactured by Nippon Bell Co., Ltd. was used for the measurement of the void amount. From this result, it was found that each of Samples F to H had voids in the particles. In addition, from the diffraction patterns of X-ray diffraction, it was confirmed that Samples F to H were Li _1.33 Ti _1.67 O ₄ .

[0029]

[Table 3]

Example 3 Lithium titanate hydrate was obtained in the same manner as in Example 2, except that the hydrothermal treatment temperature was 150 ° C.

The physical properties of the lithium titanate hydrate thus obtained were examined. As a result, this lithium titanate hydrate had a major axis of 0.8 μm as observed by an electron microscope.
It was found that it had an extremely thin plate-like shape with m, a minor axis of 0.65 μm, and a thickness of about 20 nm. Specific surface area is 13
It was 0.1 m ² / g, and the void volume was 0.327 ml / g. In addition, Bell Soap 28 manufactured by Nippon Bell Co., Ltd. was used for the measurement of the void amount. Further, it was found from the diffraction pattern of X-ray diffraction that the crystallinity was excellent. Further, according to the chemical analysis, the component ratios are as follows: Ti 43.2% by weight, Li 4.80% by weight, NH ₄ <0.01% by weight, C
l <0.005% by weight, and X-ray diffraction _{shows that} Li _1.33 T
The presence of i _1.67 O _{4 .H 2} O was confirmed. Furthermore, DS
According to C analysis, water of crystallization was released at 206 ° C. to give Li _1.33
It was found to undergo a phase transition to Ti _1.67 O ₄ and crystallize at 355 ° C.

(3) Synthesis of lithium titanate After pulverizing the lithium titanate hydrate described above in an agate mortar, 15 g of the pulverized product was weighed into an alumina crucible, 550,
Put them in an electric furnace set to 590 and 630 ° C.
It was heated and dehydrated in the atmosphere for 2 hours to obtain the lithium titanate of the present invention (Samples I to K).

The physical properties of the samples I to K thus obtained were examined. As a result, it was found by electron microscope observation that the lithium titanate was fine particles having a major axis of 0.2 to 0.3 μm and had an extremely thin plate shape. Next, Table 4 shows the measurement results of the specific surface area by the BET method and the measurement results of the void amount by nitrogen adsorption. In addition, Bell Soap 28 manufactured by Nippon Bell Co., Ltd. was used for the measurement of the void amount. From this result, it was found that Samples I to K all had voids in the particles. Further, from the diffraction pattern of X-ray diffraction, it was confirmed that Samples I to K were Li _1.33 Ti _1.67 O ₄ .

[0034]

[Table 4]

Example 4 (1) Synthesis of Titanic Acid Compound A titanic acid compound was obtained according to the method described in (1) of Example 1 above. (2) Synthesis of lithium titanate hydrate The titanate compound obtained in (1) above is repulped to give T
A slurry having an iO ₂ concentration of 55.02 g / l was obtained. The pH of this slurry was 6.90 and the conductivity was 330 μS /
cm. 3.64 l of this slurry was charged into a 5-l4 neck flask, and while cooling the ice with ice so that the temperature of the slurry was 10 to 15 ° C, an aqueous solution in which 84.97 g of lithium hydroxide monohydrate was dissolved in 360 ml of pure water was added. It was added over time and then aged for 1 hour. After completion of the addition, the pH of the slurry was 12.1, and the TiO ₂ concentration was 50 g / l. The added lithium compound is Li / Ti
The molar ratio was 0.8. Next, the slurry thus obtained was heated to 95 ° C. and reacted at that temperature for 2 hours. The reaction slurry obtained is then cooled, then filtered and then dried without washing at a temperature of 50 ° C.,
Lithium titanate hydrate was obtained.

The physical properties of the thus obtained lithium titanate hydrate were examined. As a result, it was found by electron microscope observation that the lithium titanate hydrate was an aggregate of fine particles of about 300 nm and had an extremely thin plate shape. Further, according to the chemical analysis, the component ratios thereof are Ti 44.1% by weight, Li 4.61% by weight, NH ₄
It was 0.02% by weight and Cl <0.005% by weight, and the presence of Li _1.33 Ti _1.67 O _{4 .H 2} O was confirmed by X-ray diffraction. Further, according to DSC analysis, water of crystallization was released at 348 ° C., and a phase transition to Li _1.33 Ti _1.67 O ₄ occurred, resulting in 476 ° C.
It was found to crystallize at.

(3) Synthesis of lithium titanate The lithium titanate hydrate obtained in (2) above was crushed in an agate mortar, and 15 g of the crushed product was weighed into an alumina crucible to obtain 250, 400, 500, 600. The lithium titanate of the present invention (Samples L to O) was obtained by heating in an electric furnace set to a temperature of ° C and dehydration by heating in the atmosphere for 2 hours.

The physical properties of the lithium titanate thus obtained were examined. As a result, this lithium titanate is
Observation with an electron microscope revealed that the particles were 1 μm fine particles and had an extremely thin plate shape. Next, Table 5 shows the measurement results of the specific surface area by the BET method and the measurement results of the void amount by nitrogen adsorption. From this result, the samples L to O are
It was found that each of them had voids in the particles. Further, from the diffraction pattern of X-ray diffraction, the samples L to O were Li _1.33 Ti _1.67 O ₄ , and further, as shown in Table 6, when the temperature of heat dehydration was increased, the interplanar spacing gradually widened, It was found that the value of the surface spacing described on the ASTM card was approached.

[0039]

[Table 5]

[0040]

[Table 6]

Example 5 In Example 2, after adding an aqueous lithium hydroxide solution over 1 hour, 0.138 aqueous ammonia solution of 0.138 was added.
Lithium titanate hydrate was obtained in the same manner as in Example 2, except that 1 liter of pure water and 0.238 liter of pure water were added and the mixture was stirred for 1 hour for aging. The concentration of the ammonium compound during the hydrothermal treatment is 0.5 mol / l.

The physical properties of the lithium titanate hydrate thus obtained were examined. As a result, this lithium titanate hydrate had a major axis of 0.8 μm as observed by an electron microscope.
It was found that it had an extremely thin plate-like shape with m, a minor axis of 0.65 μm, and a thickness of about 20 nm. Specific surface area is 12
It was 6.9 m ² / g, and the void volume was 0.389 ml / g. In addition, Bell Soap 28 manufactured by Nippon Bell Co., Ltd. was used for the measurement of the void amount. Further, it was found from the diffraction pattern of X-ray diffraction that the crystallinity was excellent. Further, according to the chemical analysis, the component ratios are as follows: Ti 43.0 wt%, Li 4.83 wt%, NH ₄ 0.05 wt%, Cl
<0.005% by weight, and from the X-ray diffraction, Li _1.33 Ti
The presence of _1.67 O _{4 .H 2} O was confirmed. In addition, DSC
According to the analysis, water of crystallization was released at 208 ° C. to give Li _1.33 T
It was found to undergo a phase transition to i _1.67 O ₄ and crystallize at 344 ° C.

(3) Synthesis of lithium titanate The above lithium titanate hydrate was crushed in an agate mortar, and 15 g of the crushed product was weighed into an alumina crucible 550,
Put them in an electric furnace set to 590 and 630 ° C.
It was heated and dehydrated in the atmosphere for 2 hours to obtain the lithium titanate of the present invention (Samples P to R).

The physical properties of the samples P to R thus obtained were examined. As a result, it was found by electron microscope observation that the lithium titanate was fine particles having a major axis of 0.2 to 0.3 μm and had an extremely thin plate shape. Next, Table 7 shows the measurement results of the specific surface area by the BET method and the measurement results of the void amount by nitrogen adsorption. In addition, Bell Soap 28 manufactured by Nippon Bell Co., Ltd. was used for the measurement of the void amount. From this result, it was found that each of Samples P to R had voids in the particles. Further, from the diffraction pattern of X-ray diffraction, it was confirmed that the samples P to R were Li _1.33 Ti _1.67 O ₄ .

[0045]

[Table 7]

Example 6 In Example 2, an aqueous lithium hydroxide solution was added over 1 hour, and then an aqueous 8.71N ammonia solution 0.276 was added.
Lithium titanate hydrate of the present invention was obtained in the same manner as in Example 2 except that 1 l of pure water and 0.1 l of pure water were added and the mixture was stirred for 1 hour for aging. The concentration of the ammonium compound during the hydrothermal treatment is 1.0 mol / l.

The physical properties of the lithium titanate hydrate thus obtained were examined. As a result, this lithium titanate hydrate had a major axis of 0.8 μm as observed by an electron microscope.
It was found that it had an extremely thin plate-like shape with m, a minor axis of 0.65 μm, and a thickness of about 20 nm. Specific surface area is 11
It was 3.9 m ² / g, and the void volume was 0.559 ml / g. In addition, Bell Soap 28 manufactured by Nippon Bell Co., Ltd. was used for the measurement of the void amount. Further, it was found from the diffraction pattern of X-ray diffraction that the crystallinity was excellent. Further, according to the chemical analysis, the component ratios are as follows: Ti 42.7 wt%, Li 4.97 wt%, NH ₄ 0.05 wt%, Cl
<0.005% by weight, and from the X-ray diffraction, Li _1.33 Ti
The presence of _1.67 O _{4 .H 2} O was confirmed. In addition, DSC
According to the analysis, water of crystallization was released at 209 ° C. to give Li _1.33 T
It was found to undergo a phase transition to i _1.67 O ₄ and crystallize at 334 ° C.

(3) Synthesis of lithium titanate The above lithium titanate hydrate was crushed in an agate mortar, and 15 g of the crushed product was weighed into an alumina crucible, 550,
Put them in an electric furnace set to 590 and 630 ° C.
It was heated and dehydrated in the atmosphere for 2 hours to obtain the lithium titanate of the present invention (Samples S to U).

The physical properties of the samples S to U thus obtained were examined. As a result, it was found by electron microscope observation that the lithium titanate was fine particles having a major axis of 0.2 to 0.3 μm and had an extremely thin plate shape. Next, Table 8 shows the measurement results of the specific surface area by the BET method and the measurement results of the void amount by nitrogen adsorption. In addition, Bell Soap 28 manufactured by Nippon Bell Co., Ltd. was used for the measurement of the void amount. From this result, it was found that each of Samples S to U had voids in the particles. Further, from the diffraction pattern of X-ray diffraction, it was confirmed that Samples S to U were Li _1.33 Ti _1.67 O ₄ .

[0050]

[Table 8]

Samples P to U (Examples 5 and 6) obtained in the presence of the ammonium compound during the hydrothermal treatment and Samples F to H (Example 2) obtained in the absence of the ammonium compound were used. By comparison, it was found that Samples P to U in which the ammonium compound was present had larger or similar voids, and at the same hydrothermal treatment temperature, well-shaped lithium titanate having good crystallinity was obtained. It was

Samples A to U obtained in Examples 1 to 6 above
It was confirmed that a desired negative electrode for a lithium battery and further a lithium battery can be obtained when the above method is used.

[0053]

INDUSTRIAL APPLICABILITY The present invention is a lithium titanate characterized by having voids in its particles, which can trap substances and ions such as lithium in the voids,
Furthermore, since doping and dedoping of lithium ions can be performed quickly, the characteristics of the negative electrode for lithium batteries and the like are excellent. Further, the lithium titanate of the present invention is a useful compound that can be used in various applications such as an ultraviolet absorber because the size and shape of particles are controlled.

Further, in the present invention, a step of reacting a titanium compound and an ammonium compound in water to obtain a titanate compound, and reacting the titanate compound and a lithium compound in water to obtain a lithium titanate hydrate. A method for producing lithium titanate, comprising the steps of: dehydrating the lithium titanate hydrate by heating, wherein the lithium titanate can be efficiently obtained.

Furthermore, the present invention is a lithium battery negative electrode characterized by comprising the above-mentioned lithium titanate, and further a lithium battery characterized by using the negative electrode, which is excellent. It has battery characteristics and can be used as a primary battery or a secondary battery.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the particle shape of lithium titanate (Sample C) obtained in Example 1.

2 is an X-ray diffraction pattern of lithium titanate (Sample C) obtained in Example 1. FIG.

FIG. 3 is an electron micrograph showing the particle shape of lithium titanate (Sample D) obtained in Example 1.

FIG. 4 is an X-ray diffraction pattern of the lithium titanate (Sample D) obtained in Example 1.

5 is an electron micrograph showing the particle shape of lithium titanate (Sample N) obtained in Example 4. FIG.

6 is an X-ray diffraction pattern of lithium titanate (Sample N) obtained in Example 4. FIG.

FIG. 7 is an electron micrograph showing the particle shape of lithium titanate (Sample O) obtained in Example 4.

8 is an X-ray diffraction pattern of lithium titanate (Sample O) obtained in Example 4. FIG.

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Claims (9)

[Claims] 1. Lithium titanate having voids in its particles. 2. The lithium titanate according to claim 1, which has a specific surface area in the range of 1 to 300 m ² / g. 3. The lithium titanate according to claim 1, which has a laminated structure. 4. The lithium titanate according to claim 1, having a longest particle diameter in the range of 0.1 to 50 μm. 5. A step of reacting a titanium compound and an ammonium compound in water to obtain a titanate compound, a step of reacting the titanate compound and a lithium compound in water to obtain a lithium titanate hydrate, the titanium A method for producing lithium titanate, comprising the step of heating and dehydrating lithium acid hydrate. 6. The method for producing lithium titanate according to claim 5, wherein the titanate compound and the lithium compound are hydrothermally treated in water to obtain a lithium titanate hydrate. 7. The method for producing lithium titanate according to claim 6, wherein the hydrothermal treatment is performed in the presence of an ammonium compound. 8. A negative electrode for a lithium battery, comprising the lithium titanate according to claim 1. 9. A lithium battery comprising the negative electrode according to claim 8.