JP4558229B2 - Lithium titanate, method for producing the same, and use thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to lithium titanate useful as an active material for a lithium secondary battery and a method for producing the same.
[0002]
[Prior art]
Lithium titanate, which is a lithium-titanium composite oxide, is representatively Li ₄ Ti ₅ O ₁₂ , and has a voltage of 1.5 V based on lithium when used as an active material for a secondary battery, and has a long life. It is a feature. In addition, it is a material that has a proven track record as a lithium-ion battery active material for watches, and it is an electrode material that attracts attention when the battery is enlarged due to the fact that expansion and contraction during charging and discharging can be ignored. This material is used not only as a positive electrode but also as a negative electrode active material, and the future is expected as a positive electrode / negative electrode active material of a battery.
[0003]
An attempt has been made to improve the battery characteristics of a lithium secondary battery in which lithium titanate added with a third component is synthesized and used as an active material. For example, A. D. In Robertson, Journal of the Electrochemical Society, 146 (11) 3985-3962 (1991), Fe ₁ containing Li _{1 + x} Fe _1-3x Ti _{1 + 2x} O ₄ (0.0 ≦ x ≦ 0.33) T. In Ohzuku, Journal of the Electrochemical Society, 147 (10) 3592-3597 (2000), Li [CrTi] O ₄ containing Cr is proposed. In JP 2000-277116 A, the composition is Li ₄ M _x Ti ₅ − _x O ₁₂ (wherein M is at least one of V, Nb, Mo and P, and X is 0 <X ≦ 0.45). Proposed. These are lithium titanates obtained by substituting a part of Ti in lithium titanate with the above metal.
[0004]
Japanese Patent Laid-Open No. 10-251020 is characterized in that, as a metal-substituted lithium titanate, a method for producing the same, and a lithium battery using the same, a part of the Li component is substituted with a metal having a valence of 2 or more. The metal having two or more valences is at least one metal selected from the group consisting of cobalt, nickel, manganese, vanadium, iron, boron, aluminum, silicon, zirconium, strontium, magnesium and tin, lithium titanate Has been proposed.
[0005]
As a method for synthesizing lithium titanate not containing the third component, for example, as shown in Japanese Patent Laid-Open No. 2000-302547, lithium titanate with low impurities using high-purity titanium oxide is synthesized. ing. Various studies have been made on the synthesis of lithium titanate containing the third component or high purity as described above, but the characteristics of the secondary battery of lithium titanate containing specific amounts of K ₂ O and P ₂ O ₅ The impact on stagnation has not yet been reported.
[0006]
[Problems to be solved by the invention]
In order to improve lithium secondary battery characteristics of lithium titanate, the present invention synthesizes lithium titanate containing specific amounts of K ₂ O and P ₂ O ₅ , a method for producing the same, and the lithium titanate. An object of the present invention is to provide a lithium secondary battery using.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventors have made a lithium secondary using lithium titanate containing a specific amount of K ₂ O and P ₂ O ₅ produced by a specific method as an active material. The battery was found to exhibit excellent charge / discharge characteristics, and the present invention was completed.
[0008]
That is, the lithium titanate of the present invention has a K ₂ O content of 0.10 to 0.25 % by mass and a P ₂ O ₅ content of 0.10 to 0.50 % by mass, and Li ₄ Ti ₅ O ₁₂ is a main component.
[0009]
The method for producing lithium titanate of the present invention comprises a titanium oxide having a K ₂ O content of 0.10 to 0.30 mass% and a P ₂ O ₅ content of 0.10 to 0.60 mass%, A step of uniformly mixing a water-soluble lithium salt in water such that the atomic ratio of Li and Ti is 4: 5, a step of drying the mixture to form spherical particles, and And a step of heat treatment in the atmosphere .
[0010]
The lithium titanate can be used as a positive electrode active material to form a positive electrode for a battery.
[0011]
Moreover, it can also be set as the negative electrode for batteries using the said lithium titanate as a negative electrode active material.
[0012]
Moreover, a lithium secondary battery can be formed using the battery positive electrode or the battery negative electrode.
[0013]
Furthermore, the lithium secondary battery was prepared using the lithium titanate as a positive electrode active material and a metal Li as a negative electrode, and the charge / discharge test results were a charge / discharge voltage of 1.4 to 1.6 V and 150 mAh. A lithium secondary battery having an initial discharge capacity of / g or more can be formed.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The lithium titanate of the present invention has a K ₂ O content of 0.10 to 0.25% by mass and a P ₂ O ₅ content of 0.10 to 0.50% by mass. In addition, the main component is Li ₄ Ti ₅ O ₁₂ , which is, for example, an X-ray diffraction diagram using powder having a peak intensity of 4.83Å which is the main peak of Li ₄ Ti ₅ O _12. When 100 is set, the peak intensity of 3.25% which is the main peak of rutile titanium dioxide and 2.07% which indicates the formation of Li ₂ TiO ₃ is preferably 5 or less, more preferably 3 or less. .
[0015]
The method for producing lithium titanate according to the present invention typically includes a step of uniformly mixing raw materials in water, a step of drying the mixture to form spherical particles, and a step of heat-treating the spherical particles in the air. Since the washing process is not included, the target product can be manufactured without considering the environmental impact of the drainage.
[0016]
In the method for producing lithium titanate of the present invention, lithium hydroxide, lithium hydroxide monohydrate, lithium oxide, lithium hydrogen carbonate, lithium carbonate or the like is first mixed or dissolved in water as a lithium salt. Titanium oxide having an atomic ratio of Li and Ti of 4: 5 is mixed with this liquid. The slurry concentration of the mixed solution is preferably 0.48 to 4.8 mol / L for the Li raw material and 0.60 to 6.00 mol / L for the titanium oxide. When the concentration is higher than the above range, a strong stirring force is required for uniform mixing. Moreover, it becomes a cause of trouble, such as piping blockage at the time of drying, and is not preferable. If the concentration is lower than the above range, the amount of evaporated water increases, and the drying cost increases, which is not preferable. The mixture is dried with stirring to give spherical particles. As the method of drying into spherical particles, spray drying, fluidized bed drying, rolling granulation drying, or freeze drying can be used alone or in combination. The dried product is heat-treated in the atmosphere.
[0017]
The heat treatment temperature is 700 to 1000 ° C. for 1 to 10 hours, but preferably 800 to 900 ° C. for 5 to 10 hours. If it is less than 700 degreeC, reaction of a titanium oxide and a lithium compound is not enough. When the temperature exceeds 1000 ° C., sintering of lithium titanate occurs, resulting in poor battery characteristics.
[0018]
The titanium oxide used as the production raw material has a K ₂ O content of 0.10 to 0.30 mass% and a P ₂ O ₅ content of 0.10 to 0.60 mass%. In the present production method, if the K ₂ O content and the P ₂ O ₅ content are less than the above ranges, the secondary battery characteristics of lithium titanate obtained as in the comparative example described later are unfavorable. Also, the clay increases upon mixing with an aqueous lithium salt solution content of K 2 _O and P ₂ O ₅ content exceeds the above range, a strong stirring force to the uniform mixing is required. Moreover, it causes troubles such as piping blockage during drying, which is not preferable.
[0019]
The titanium oxide as the raw material is typically produced by adding K ₂ O and P ₂ O ₅ to hydrous titanium oxide so as to have the above content, followed by firing and pulverization.
[0020]
A coin type secondary battery using the lithium titanate synthesized as described above as a positive electrode active material and using Li metal as a negative electrode was prepared, and battery characteristics were evaluated. According to the lithium titanate of the present invention, the result of the charge / discharge test satisfies a charge / discharge voltage of 1.4 to 1.6 V, and Li ₄ Ti ₅ O ₁₂ does not contain K ₂ O and P ₂ O _5. Also found a large initial discharge capacity. When the lithium titanate of the present invention is used as a negative electrode active material, a lithium ion battery is provided using a Li-containing composite oxide such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₂ , LiFeO _{2 for} the positive electrode, Contributes to the improvement of charge / discharge characteristics.
[0021]
【Example】
Examples and Comparative Examples of the present invention will be described with reference to the drawings, but the present invention is not limited to these Examples.
[0022]
[Example 1]
Lithium hydroxide (LiOH.H ₂ O) was dissolved in water at a concentration of 12%. Titanium oxide having a K ₂ O content of 0.26% by mass and a P ₂ O ₅ content of 0.51% by mass was added to the solution for 30 minutes after adding an amount of an atomic ratio of Li to Ti of 4: 5. Stir above. The mixture is spray dried at 110 ° C. The dried product was heat treated in the atmosphere at 875 ° C. for 6 hours to produce lithium titanate.
[0023]
This sample was subjected to X-ray diffraction using Cu as a target, measurement of specific surface area, and measurement of average particle diameter. FIG. 1 shows an X-ray diffraction diagram. From FIG. 1, it was confirmed that the synthesized product was Li ₄ Ti ₅ O ₁₂ . The obtained sample had a specific surface area of 2.7 m ² / g and an average particle diameter (median diameter) of 23.9 μm. The K ₂ O content and the P ₂ O ₅ content in the composite by ICP analysis were 0.230% by mass and 0.439% by mass, respectively. Further, the Li / Ti molar ratio of the composite was 0.80.
[0024]
Next, a positive electrode mixture was prepared using the lithium titanate as an active material. 82 parts by weight of lithium titanate obtained as an active material, 9 parts by weight of acetylene black as a conductive additive, 9 parts by weight of a fluororesin as a binder, and n-methyl-2-pyrrolidone as a solvent were mixed. The electrode mixture was applied to an aluminum foil by a doctor blade method so that the thickness after drying was 0.01 g / cm ² . After vacuum drying at 150 ° C., roll pressing was performed to 80% of the thickness of the initial electrode mixture. After punching out with an area of 1 cm 2, the positive electrode 4 of the coin battery shown in FIG. 2 was obtained.
[0025]
In FIG. 2, the negative electrode 5 was a metal Li plate, the electrolyte was a solution of LiPF ₆ dissolved in an equal volume mixture of ethylene carbonate and dimethyl carbonate at 1 mol / L, and the separator was a polypropylene porous film.
[0026]
Using the coin battery produced as described above, the battery was discharged to 1.0 V with a constant current of 0.2 mA / cm ² and then charged to 3.0 V, and this cycle was repeated 10 times. FIG. 3 shows a discharge curve of a coin battery in which lithium titanate of this example is used as a positive electrode active material and Li metal is used as a negative electrode. The discharge capacity at the third cycle was 164 mAh / g, and the discharge capacity at the 10th cycle was 163 mAh / g.
[0027]
[Example 2]
A dried product was obtained in the same manner as in Example 1 except that titanium oxide having a K ₂ O content of 0.27% by mass and a P ₂ O ₅ content of 0.50% by mass was used. The dried product was heat-treated at 800 ° C. for 6 hours in the atmosphere. In the same manner as in Example 1, the X-ray diffraction qualities, the specific surface area and the average particle diameter were measured, and the K ₂ O, P ₂ O ₅ and Li / Ti molar ratios were analyzed. Coin battery evaluation was also performed in the same manner as in Example 1. The X-ray diffraction result was the same as in Example 1, and it was confirmed that the synthesized product was Li ₄ Ti ₅ O ₁₂ . The specific surface area was 2.8 m ² / g and the average particle diameter (median diameter) was 8.7 μm. The amounts of K ₂ O and P ₂ O ₅ in the composite were 0.232% by mass and 0.432% by mass, respectively. The Li / Ti molar ratio was 0.82. As a result of the coin battery evaluation, the discharge capacity at the third cycle was 164 mAh / g, and the discharge capacity at the 10th cycle was 162 mAh / g.
[0028]
[Example 3]
Synthesis and evaluation were performed in the same manner as in Example 1 except that titanium oxide having a K ₂ O content of 0.20% by mass and a P ₂ O ₅ content of 0.13% by mass was used. From the X-ray diffraction result, it was confirmed that the synthesized product was Li ₄ Ti ₅ O ₁₂ . The specific surface area was 2.3 m ² / g and the average particle diameter (median diameter) was 24.7 μm. The amounts of K ₂ O and P ₂ O ₅ in the synthesized product by ICP analysis were 0.170% by mass and 0.109% by mass, respectively. The Li / Ti molar ratio was 0.83. As a result of the coin battery evaluation, the discharge capacity at the third cycle was 160 mAh / g, and the discharge capacity at the 10th cycle was 158 mAh / g.
[0029]
[Example 4]
Synthesis and evaluation were performed in the same manner as in Example 1 except that titanium oxide having a K ₂ O content of 0.16% by mass and a P ₂ O ₅ content of 0.27% by mass was used. From the X-ray diffraction result, it was confirmed that the synthesized product was Li ₄ Ti ₅ O ₁₂ . The specific surface area was 2.2 m ² / g and the average particle diameter (median diameter) was 20.1 μm. The amounts of K ₂ O and P ₂ O ₅ in the synthesized product by ICP analysis were 0.139% by mass and 0.235% by mass, respectively. The Li / Ti molar ratio was 0.83. As a result of the coin battery evaluation, the discharge capacity at the third cycle was 159 mAh / g, and the discharge capacity at the 10th cycle was 157 mAh / g.
[0030]
[Example 5]
Synthesis and evaluation were performed in the same manner as in Example 1 except that titanium oxide having a K ₂ O content of 0.28 mass% and a P ₂ O ₅ content of 0.33 mass% was used. From the X-ray diffraction result, it was confirmed that the synthesized product was Li ₄ Ti ₅ O ₁₂ . The specific surface area was 1.6 m ² / g and the average particle diameter (median diameter) was 15.1 μm. The amounts of K ₂ O and P ₂ O ₅ in the synthesized product by ICP analysis were 0.243% by mass and 0.284% by mass, respectively. The Li / Ti molar ratio was 0.83. As a result of the coin battery evaluation, the discharge capacity at the third cycle was 156 mAh / g, and the discharge capacity at the 10th cycle was 154 mAh / g.
[0031]
[Comparative Example 1]
Synthesis and evaluation were performed in the same manner as in Example 1 except that titanium oxide having a K ₂ O content of less than 0.01% by mass and a P ₂ O ₅ content of less than 0.01% by mass was used. From the X-ray diffraction result, it was confirmed that the synthesized product was Li ₄ Ti ₅ O ₁₂ . The specific surface area was 2.2 m ² / g and the average particle diameter (median diameter) was 22.1 μm. The amounts of K ₂ O and P ₂ O ₅ in the synthesized product by ICP analysis were both 0.001% by mass or less. The Li / Ti molar ratio was 0.83. As a result of the coin battery evaluation, the discharge capacity at the third cycle was 146 mAh / g, and the discharge capacity at the 10th cycle was 136 mAh / g.
[0032]
As described above, in the production method of the present invention, lithium titanate containing 0.10 to 0.30 % by mass of K ₂ O and 0.10 to 0.60 % by mass of P ₂ O ₅ is K ₂ O and The initial discharge capacity is larger than that of lithium titanate not containing P ₂ O ₅ .
[0033]
【The invention's effect】
As described above, the lithium titanate of the present invention contains 0.10 to 0.25 % by mass of K ₂ O and 0.10 to 0.50 % by mass of P ₂ O _5. Can obtain lithium titanate having a larger initial discharge capacity than lithium titanate not containing K ₂ O and P ₂ O ₅ .
[Brief description of the drawings]
FIG. 1 is an X-ray diffraction pattern of lithium titanate of Example 1 of the present invention.
FIG. 2 is a cross-sectional view of a coin battery using lithium titanate according to an embodiment of the present invention as a positive electrode.
FIG. 3 is a graph showing a discharge curve of a coin battery using lithium titanate of Example 1 of the present invention and lithium titanate of Comparative Example 1 as positive electrodes.
[Explanation of symbols]
4 Positive electrode 5 Negative electrode

Claims (6)

K ₂ O content is 0.10 to 0.25% by mass, P ₂ O ₅ content is 0.10 to 0.50% by mass, and Li ₄ Ti ₅ O ₁₂ is the main component. Features lithium titanate. Titanium oxide having a K ₂ O content of 0.10 to 0.30% by mass and a P ₂ O ₅ content of 0.10 to 0.60% by mass, a water-soluble lithium salt, Li and Ti A step of uniformly mixing in water such that the atomic ratio is 4: 5, a step of drying the mixture to form spherical particles, and a step of heat-treating the spherical particles in the air. A method for producing lithium titanate.   A positive electrode for a battery using the lithium titanate according to claim 1 as a positive electrode active material.   A negative electrode for a battery using the lithium titanate according to claim 1 as a negative electrode active material.   A lithium secondary battery using the battery positive electrode according to claim 3 or the battery negative electrode according to claim 4. A lithium secondary battery manufactured using the lithium titanate according to claim 1 as a positive electrode active material and a metal Li as a negative electrode, and a charge / discharge test result of 1.4 to 1.6 V A lithium secondary battery having a voltage and an initial discharge capacity of 150 mAh / g or more.

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