JP2001240498A - High crystalline lithium titanate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain lithium titanate with high capacity density in charging and discharging, which is useful as an active material for lithium secondary battery. SOLUTION: When manufacturing high crystalline lithium titanate consisting of Li4/3Ti5/3O4 as a main component and few other components, Li and Ti compounds are wet mixed, uniformly dried in spherical shape, and synthesized through heat treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly crystalline lithium titanate useful as an active material of a lithium secondary battery.

[0002]

2. Description of the Related Art Lithium titanate, which is a lithium-titanium composite oxide, has a general formula Li _{(1 + X)} Ti _(2-X) O _y (x = −
0.2 to 1.0, y = 3 to 4), representative of which are Li _4/3 Ti _5/3 O ₄ , LiTi ₂ O ₄ , and Li ₂ Ti
O _{3 and the} like are known. These are 1.5V based on lithium.
And a long service life. Among them, Li _4/3 Ti _5/3 O ₄ has attracted attention because of its large charge / discharge capacity. Also, Li _4/3 Ti _5/3 O ₄ is a material that has a proven track record as a lithium-ion battery active material for watches, and is characterized by its negligible expansion and contraction during charge / discharge, and is attracting attention in increasing the size of batteries. It is an electrode material. This material has not only been used as a conventionally used positive electrode active material but also as a negative electrode active material, and its future is expected as a positive electrode and negative electrode active material for batteries.

As a method for producing lithium titanate, JP-A-6-275263 discloses that lithium hydroxide or lithium carbonate is used as a lithium compound, and this and titanium oxide are subjected to dry heat treatment at a temperature of 700 ° C. to 1600 ° C. A method is described.

JP-A-9-309726 discloses a process of reacting a titanium compound and an ammonia compound in water to obtain a titanate compound, and a process of reacting the titanate compound and a lithium compound in water. A method for producing lithium titanate hydrate is disclosed.

However, if the lithium titanate Li _4/3 Ti _5/3 O ₄ obtained by these methods were used as the positive electrode active material to form a lithium secondary battery, charging and discharging capacity was about 130～150MAh / g (Electrochemistry vol. 62, No. 9 (1994) P870-875).
reference). The theoretical capacity of lithium titanate is 175 mAh
/ G (see WO99 / 03784, etc.), but at present, the charge / discharge capacity of the lithium titanate is much lower than the theoretical capacity.

On the other hand, in recent years, in lithium secondary batteries using lithium titanate, development of a material having a larger charge / discharge capacity has been desired.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object of the present invention is to provide lithium titanate having a high charge / discharge capacity, which is closer to 175 mAh / g, which is the theoretical capacity of lithium titanate. With the goal.

[0008]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that a lithium ion battery made using a specific lithium titanate exhibits excellent charge / discharge characteristics. And completed the present invention.

That is, the highly crystalline lithium titanate of the present invention contains Li _4/3 Ti _5/3 O ₄ as a main component, and has a main peak intensity of Li _4/3 Ti _5/3 O _{4 determined} by an X-ray diffraction method. To 100
When the anatase type titanium dioxide, the rutile type titanium dioxide, and the main peak intensity of Li ₂ TiO ₃ are all lithium titanate of 5 or less, and the crystallite diameter thereof is 700 ° to 800 ° It is characterized by.

When this highly crystalline lithium titanate is used as a positive electrode active material in a lithium secondary battery, the initial charge / discharge capacity can be 165 mAh / g or more.

[0011]

Highly crystalline lithium titanate of the present invention DETAILED DESCRIPTION OF THE INVENTION, the main component is characterized in that it consists of _{Li 4/3 Ti 5/3 O 4, Li} 4 in the X-ray diffraction diagram using powder or the like _{/ 3} T
When the peak intensity of the main peak of i _5/3 O ₄ at 4.83 ° is defined as 100, 3.51 ° which is the main peak of anatase type titanium dioxide, 3.25 ° which is the main peak of rutile type titanium dioxide, and Each peak intensity at 2.07 °, which indicates the production of Li ₂ TiO ₃ , is 5 or less, preferably the total is 10 or less, and most preferably each peak intensity is 3 or less. That is, in the present invention, L
It is characterized in that products other than i _4/3 Ti _5/3 O ₄ are trace amounts. Further, the crystallite diameter is 700 to 800, preferably 730 to 780, and the crystallinity is extremely high. The crystallite diameter can be determined, for example, by the Scherrer's formula from the half width of the peak at 4.83 °.

Further, when a lithium secondary battery of a non-aqueous solvent system is manufactured using the above-mentioned lithium titanate as a positive electrode active material and, for example, metal Li as a negative electrode, a charge / discharge test shows that a charge / discharge of 1.5 V results. Voltage, and 165 mAh /
g and a high initial charge / discharge capacity of at least g. As described above, the excellent charge / discharge characteristics are such that the peak intensity of the product other than Li _4/3 Ti _5/3 O _{4 of the} lithium titanate of the present invention is as small as 5 or less, and the crystallite diameter is small. Is 70
It is considered to be due to the extremely high crystallinity in the range of 0 ° to 800 °.

In order to produce the highly crystalline lithium titanate of the present invention, for example, lithium hydroxide, lithium hydroxide monohydrate, lithium oxide,
Mix or dissolve lithium bicarbonate or lithium carbonate with water. Anatase-type titanium dioxide or hydrous titanium oxide is mixed with this solution so that the atomic ratio of Li and Ti is 4: 5. The slurry concentration of the mixture was 0.48 to 4.8 mol / L for the Li raw material and 0.60 to 6.00 for the Ti raw material.
Mol / L is preferred. If the concentration is higher than the above range, a strong stirring force is required for uniform mixing. Also, it is not preferable because it causes troubles such as blockage of the piping during drying. On the other hand, if the concentration is lower than the above range, the amount of evaporated water increases, and the drying cost is undesirably increased. Next, the mixture is dried with stirring to obtain spherical particles. As the method of drying into spherical particles, spray drying, fluidized bed drying, tumbling granulation drying, or freeze drying can be used alone or in combination. Further, the dried product is heat-treated in a gas stream. The feature of this production method is that the Li compound and the Ti compound are uniformly mixed, the composition of the target is not misaligned, and the composition and structure of the inside and the surface of the target are less different. This is also presumed to be a cause of having a high charge / discharge capacity.

The gas for the heat treatment may be any of nitrogen, oxygen and air, but firing in an oxygen gas stream is preferred. The reason is that the lithium titanate has higher crystallinity by firing in an oxygen stream, and as a result, a higher discharge capacity can be obtained. The target product can also be obtained by pulverizing these heat-treated products.

The heat treatment temperature is preferably from 700 to 1000 ° C, more preferably from 750 to 950 ° C. If the temperature is lower than 700 ° C., the reaction between the titanium oxide and the lithium compound is not sufficient, which is not preferable. When the temperature exceeds 1000 ° C., Li ₂ Ti ₃ other than the lithium titanate Li _4/3 Ti _5/3 O _{4 of} the present invention is used.
O ₇ is generated, which is not preferable.

The starting material of the titanium oxide used as the production material may be any of chloride, sulfate, organic salt and the like. The crystal structure may be any of an anatase type and an amorphous type. However, as in the present invention, in order to obtain lithium titanate having excellent discharge capacity and battery characteristics, an anatase type is required. It is preferred to use titanium dioxide or hydrous titanium oxide. Anatase type titanium dioxide must have a purity of at least 95% or more,
Preferably it is 98% or more. When the purity is less than 95%, the capacity per active material weight is reduced, which is not preferable. On the other hand, high purity, for example, 99.99% purity can be used, but in this case, the cost is increased. Further, when considered as an electrode active material, if the content is 98% or more, the influence of the composition and the crystallinity is larger, and the meaning of high purification is reduced. When hydrous titanium oxide is calcined to form an anatase type titanium dioxide, the content falls within the above range, and the purity standard before calcining is 90% or more. The reason is the same as the above-mentioned anatase type titanium oxide.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments and comparative examples of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.

[0018]

Embodiment 1 First, lithium hydroxide (LiOH.H
_TwoO) Add 1.962 mol to 451 g of water,
I understand. 98% pure anatase titanium oxide in solution
To TiO _Two2.453 mol was added and stirred. this
In this case, the atomic ratio of Li to Ti is 4: 5. Mixed slurry
Has a volume of 0.502 L, and a Li raw material and Ti before drying.
The original slurry concentrations were 3.91 mol / L and 4.
89 mol / L. The mixture was spray dried at 110 ° C
Thereafter, the dried product is heat-treated at 800 ° C. for 6 hours in an oxygen gas stream.
Thus, lithium titanate was produced.

This lithium titanate targets Cu.
X-ray diffraction results showed that Li_4/3Ti_5/3O_FourMain Pi
When the peak intensity of 4.83% which is
The main peak of anatase type titanium dioxide
3.51%, and the main peak of rutile titanium dioxide
3.25 ° is less than or equal to 1, respectively.
i _TwoTiO_ThreeThe peak intensity at 2.07 ° indicating the formation of
there were. The crystallite diameter was 736 °.

Next, a positive electrode mixture was prepared using the above lithium titanate as an active material. 82 parts by weight of lithium titanate obtained as an active material, 10 parts by weight of acetylene black as a conductive additive, and 8 parts by weight of a fluororesin as a binder were mixed using n-methyl-2-pyrrolidone as a solvent. The electrode mixture was applied to a copper foil by a doctor blade method so that the thickness after drying was 0.03 g / cm ² . 1
After vacuum drying at 50 ° C, 80% of initial electrode mixture thickness
Roll pressed. After punching in an area of 1 cm ² , a positive electrode 4 of a coin battery as shown in FIG. 1 was obtained.

In FIG. 1, a negative electrode 5 is a metal Li plate, an electrolytic solution is a mixture obtained by dissolving 1 mol / L of LiPF ₆ in an equal volume mixture of ethylene carbonate and dimethyl carbonate, and a separator 6 is a porous polypropylene film. 1. Positive electrode case containing positive electrode and negative electrode respectively The overall size of the battery including the negative electrode case 1 is approximately 20 mm in outer shape,
The height was about 3 mm.

Using the coin battery prepared as described above, the battery was discharged to 1.0 V at a constant current of 0.4 mA / cm ² and then charged to 3.0 V.
Repeated times.

[0023]

Example 2 Lithium titanate was synthesized in the same manner as in Example 1 except that the heat treatment was performed at 875 ° C. in an oxygen gas stream. The following evaluation was performed in the same manner as in Example 1.

As a result of X-ray diffraction of this lithium titanate using Cu as a target, when the peak intensity of 4.83 °, which is the main peak of Li _4/3 Ti _5/3 O ₄ , is set to 100, anatase type titanium dioxide is used. which is the main peak peak intensity of 3.51Å is 1 or less, both the peak intensity of the 2.07Å showing the generation of 3.25Å peak intensity and Li ₂ TiO ₃ as a main peak of the rutile titanium dioxide It was 2. The crystallite diameter was 757 °.

[0025]

Example 3 A dried product obtained under the same conditions as in Example 1 was heat-treated at 850 ° C. for 6 hours in a stream of N ₂ gas to obtain lithium titanate. The following evaluation was performed in the same manner as in Example 1.

As a result of X-ray diffraction using Cu as a target, when the peak intensity of 4.83 ° which is the main peak of Li _4/3 Ti _5/3 O ₄ is set to 100, anatase type titanium dioxide is used. 3.51 °, which is the main peak of the above, 3.25 ° which is the main peak of the rutile-type titanium dioxide, and 2.07 which indicates the production of Li ₂ TiO _3.
The peak intensity of Å was 1 or less. The crystallite diameter was 732 °.

[0027]

Example 4 A dried product obtained under the same conditions as in Example 1 was heat-treated in an air stream at 900 ° C. for 10 hours to obtain lithium titanate. The following evaluation was performed in the same manner as in Example 1.

This lithium titanate targets Cu
X-ray diffraction results showed that Li_4/3Ti_5/3O_FourMain Pi
When the peak intensity of 4.83% which is
The main peak of anatase type titanium dioxide
3.51%, and the main peak of rutile titanium dioxide
3.25 ° is less than or equal to 1, respectively.
i _TwoTiO_ThreeThe peak intensity at 2.07 ° indicating the formation of
there were. The crystallite diameter was 773 °.

[0029]

Comparative Example 1 A saturated aqueous solution of lithium hydroxide (LiOH.H ₂ O) and anatase-type titanium oxide were mixed at a molar ratio of 4: 5, and dried at 110 ° C. for 12 hours. After the dried product was mixed and pulverized, it was heat-treated at 800 ° C. for 6 hours in a nitrogen gas stream. The following evaluation was performed in the same manner as in Example 1.

As a result of X-ray diffraction using Cu as a target, when the peak intensity of 4.83 ° which is the main peak of Li _4/3 Ti _5/3 O ₄ is set to 100, the anatase type titanium dioxide is used. The peak intensity at 3.51 °, which is the main peak of, is 1 or less, and the peak intensity at 3.25 °, which is the main peak of rutile titanium dioxide, is 2.
2. The peak intensity at 2.07 ° indicating the production of Li ₂ TiO ₃ was 9. The crystallite diameter was 692 °.

[0031]

Comparative Example 2 A dried and ground product obtained in the same manner as in Comparative Example 1 was heat-treated at 800 ° C. for 6 hours in an oxygen gas stream. The following evaluation was performed in the same manner as in Example 1.

As a result of X-ray diffraction using Cu as a target, when the peak intensity of 4.83 ° which is the main peak of Li _4/3 Ti _5/3 O ₄ was set to 100, anatase type titanium dioxide was used. The peak intensity at 3.51 °, which is the main peak of, is 1 or less, and the peak intensity at 3.25 °, which is the main peak of rutile titanium dioxide, is 2.
0, the peak intensity at 2.07 ° indicating the production of Li ₂ TiO ₃ was 9. The crystallite diameter was 704 °.

Table 1 shows the X-ray diffraction peak intensities, crystallite diameters, and initial discharge capacity values of the coin batteries of Examples 1 to 4 and Comparative Examples 1 and 2.

[0034]

[Table 1]

FIG. 2 shows the discharge characteristics of the coin batteries using the lithium titanates of Examples 1-4 and Comparative Examples 1-2.

As is clear from the results shown in Table 1 and FIG. 2, the battery voltages of Examples 1 to 4 and Comparative Examples 1 and 2 satisfy the theoretical voltage of 1.5 V. While the discharge capacity was as high as 165 mAh / g or more, Comparative Example 1
And Comparative Example 2 were 120 mAh / g and 137 mAh / g
And the initial discharge capacity was low. Thus, the lithium titanate of the present invention has a theoretical capacity density of 175 mAh / g.
It can be seen that a high discharge capacity close to

[0037]

As described above, according to the present invention, the high crystallinity
Lithium titanate is Li_4/3Ti_5/3O _FourIs the main component,
Li by X-ray diffraction method_4/3Ti_5/3O_FourMain peak strength
When the degree is 100, anatase type titanium dioxide,
Chill type titanium dioxide and Li_TwoTiO_ThreeMain peak of
Lithium titanate whose strength is 5 or less
And the crystallite diameter is 700-800 °
165 mAh / g close to the theoretical capacity
The high discharge capacity described above indicates that the electrode
It is extremely useful as a substance.

[Brief description of the drawings]

FIG. 1 is a sectional view of a coin battery using lithium titanate as a positive electrode active material according to one embodiment of the present invention.

FIG. 2 is a discharge characteristic diagram of a coin battery using lithium titanate of Examples 1 to 4 and Comparative Examples 1 and 2.

[Explanation of symbols]

 4 Positive electrode 5 Negative electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyoshi Nakahara 1978 Kogushi, Ube City, Yamaguchi Prefecture 25-Titan Industry Co., Ltd. F-term (reference) 4G077 AA01 BC42 CA03 EC02 HA20 5H050 AA08 BA16 BA17 CA07 CB12 EA10 EA24 FA19 HA13 HA19

Claims (2)

[Claims] 1. Anatase-type titanium dioxide containing Li _4/3 Ti _5/3 O ₄ as a main component and the main peak intensity of Li _4/3 Ti _5/3 O _{4 determined} by X-ray diffraction as 100. Highly crystalline lithium titanate in which rutile-type titanium dioxide and Li ₂ TiO ₃ are each lithium titanate whose main peak intensity is 5 or less, and whose crystallite diameter is 700 ° to 800 °. 2. The highly crystalline lithium titanate according to claim 1, wherein the initial charge / discharge capacity is 165 mAh / g or more when used as a positive electrode active material in a lithium secondary battery.