JP2016050156A - Method for producing lithium titanate and method for producing lithium ion secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a method for producing lithium titanate having a stable crystal structure, having almost no loss of electric capacitance during high-speed charging and discharging of a lithium ion secondary battery, having a high discharge capacity and excellent charge and discharge cycle characteristics and having excellent safety; and a method for producing a lithium ion secondary battery using the lithium titanate produced by the new production method.SOLUTION: There is provided a method for producing lithium titanate by subjecting lithium titanate having oxygen deficiency to heat treatment at 400 to 600°C in an atmosphere containing an oxidative gas, in which the lithium titanate having oxygen deficiency is preferably calcined in an inert gas atmosphere.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing lithium titanate suitable as an electrode for a lithium ion secondary battery and a method for producing a lithium ion secondary battery using the same.

Lithium secondary batteries have been rapidly spreading in recent years because of their excellent cycle characteristics. Electrode active materials of lithium secondary batteries, particularly negative electrode active materials, have a high discharge potential and are highly safe, such as an alkali metal titanate compound, for example, a lithium titanium compound having a spinel structure or a ramsdellite structure. Titanium compounds are attracting attention. In particular, spinel type lithium titanate has a theoretical capacity of 175 mAh / g and a small volume change during charge / discharge, and thus has excellent cycle characteristics.
As a method for producing spinel type lithium titanate, a mixture of one or more of lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxide and titanium oxide is calcined at 670 ° C. or higher and lower than 800 ° C. Preparing a composition composed of TiO ₂ and Li ₂ TiO ₃ or a composition composed of TiO ₂ , Li ₂ TiO ₃ and Li ₄ Ti ₅ O ₁₂ , and then subjecting to the main firing, or the above There has been proposed a method of performing main firing at 800 ° C. to 950 ° C. in an atmosphere having an oxygen gas partial pressure of 1 Pa or less after calcination (Patent Documents 1 and 2).
Lithium titanate obtained by such a method has a high discharge capacity and excellent charge / discharge cycle characteristics when used as an electrode active material of a lithium ion secondary battery, and further has a higher discharge capacity, and There is a demand for lithium titanate having excellent charge / discharge cycle characteristics.

On the other _hand, in the synthesis of the Li ₄ Ti _{5 O 12,} at the stage of the firing, and firing in an atmosphere containing a reducing _agent, the form of an oxygen deficient state of the _{Li 4 Ti 5 O 12 Li 4} Ti 5 O 12-X It has been proposed to use lithium titanate as an active material for battery materials (Patent Documents 3 and 4).
However, this lithium titanate creates an oxygen defect from a spinel structure that is inherently stable, and therefore the crystal structure is unstable. In addition, this technique for obtaining lithium titanate uses a reducing agent of hydrogen, hydrocarbons, and carbon monoxide in order to create a reducing atmosphere, and it is necessary to pay close attention to explosions. It is also a dangerous task.

Japanese Patent Publication No. 2000-302547 Japanese Patent Publication No. 2001-213623 Japanese Patent Publication No. 2011-520552 Patent publication 2010-517223

  The present invention provides titanium having stable crystal structure, little loss of electric capacity during high-speed charge / discharge of lithium ion secondary battery, higher discharge capacity, excellent charge / discharge cycle characteristics, and excellent safety. It aims at providing the manufacturing method of a lithium ion secondary battery using the manufacturing method of lithium acid, and the lithium titanate manufactured using this novel manufacturing method.

As a result of intensive studies by the present inventors to solve the above-mentioned problems, surprisingly, Li ₄ Ti ₅ O _12-X , which is lithium titanate having oxygen vacancies, was once generated, and this was generated in the atmosphere. By performing heat treatment in an atmosphere containing an oxidizing gas such as oxygen and eliminating oxygen vacancies, it is possible to obtain lithium titanate with excellent battery charge / discharge rate and high-speed charge / discharge when used as a negative electrode material, and a stable crystal structure Furthermore, it has been found that lithium titanate having oxygen vacancies is easily generated by carrying out the main firing in an inert gas atmosphere.

The present invention has been obtained based on such knowledge and is as follows.
(1) A method for producing lithium titanate, in which lithium titanate having oxygen vacancies is heat-treated at 400 ° C. to 600 ° C. in an atmosphere containing an oxidizing gas.
(2) The method for producing lithium titanate according to the above (1), wherein the lithium titanate having oxygen deficiency is fired in an inert gas atmosphere.
(3) A paste containing lithium titanate obtained by the manufacturing method of (1) or (2), a binder, and a conductive material is applied onto a current collector, and the current collector and the current collector are applied. The manufacturing method of a lithium ion secondary battery including the process of producing the electrode which has a lithium titanate layer accumulate | stored on the body.

  When the lithium titanate obtained by the method of the present invention is used as an electrode active material of a lithium ion secondary battery, there is little loss of electric capacity during high-speed charge / discharge of the lithium ion secondary battery. Therefore, compared to conventional lithium ion secondary batteries, charging defects due to high-speed charge / discharge are few, stable high-speed charge / discharge is possible, discharge capacity is high, and charge / discharge cycle characteristics are excellent.

According to the method for producing lithium titanate of the present invention, lithium titanate having oxygen vacancies is heat-treated at 400 ° C. to 600 ° C. in an atmosphere containing an oxidizing gas. When used as an active material of a battery electrode, a lithium ion secondary battery with little loss of electric capacity can be obtained during high-speed charge / discharge.
The lithium titanate of the present invention is represented by the general formula Li _x Ti _y O ₁₂ , for example, Li _{4 + x} Ti ₅ O ₁₂ (0 ≦ x ≦ 3) having a spinel structure, or Li _{2 + y} Ti ₃ having a ramsteride structure. O ₇ (0 ≦ y ≦ 3) may be mentioned. Those having a spinel structure are particularly preferred.

The lithium titanate having an oxygen vacancy according to the present invention includes lithium hydroxide, lithium carbonate, or a mixture thereof as a lithium raw material, titanium oxide, metatitanic acid, orthotitanic acid, or a mixture thereof as a titanium raw material, and lithium titanium. Li ₂ TiO ₃ , Li ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₆ O ₁₃ , Li ₂ Ti ₈ O ₁₆ or a mixture thereof is used as a raw material, and these mixed powders are obtained by firing under specific firing conditions. be able to.

  The lithium raw material lithium hydroxide or lithium carbonate preferably has a high purity, and usually has a purity of 99.0% by mass or more. Further, it is desirable that water contained in lithium hydroxide and lithium carbonate is sufficiently removed, and the content is preferably 0.1% by mass or less. Further, those having an average particle diameter (measured by a laser diffraction method) of 0.01 to 100 μm are preferable. In particular, in the case of lithium carbonate, 50 μm or less is preferable, more preferably 5 μm or less, and still more preferably 0.5 μm or less.

It is desirable that the titanium raw material titanium oxide, metatitanic acid, orthotitanic acid, or a mixture thereof is also highly pure, preferably a purity of 99.0% by mass or more, more preferably 99.5% by mass or more, Fe, Al, Si and Na contained as impurities are each less than 20 ppm, and Cl is preferably less than 500 ppm. More preferably, the contents of Fe, Al, Si and Na are each less than 10 ppm, and Cl is less than 100 ppm, more preferably less than 50 ppm. When titanium oxide is used as the titanium raw material, the specific surface area is preferably 5 m ² / g or more, more preferably 10 m ² / g or more, and further preferably 15 m ² / g or more.

It is desirable that Li ₂ TiO ₃ , Li ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₆ O ₁₃ , Li ₂ Ti ₈ O ₁₆ , or a mixture thereof used as the lithium titanium raw material is also highly pure, and the purity is 99.0% by mass. The above is preferable, more preferably 99.5% by mass or more, and Fe, Al, Si and Na contained as impurities are each less than 20 ppm, and Cl is less than 500 ppm. More preferably, Fe, Al, Si and Na are each less than 10 ppm, and Cl is less than 100 ppm, more preferably less than 50 ppm.

In synthesizing lithium titanate having oxygen vacancies, first, the lithium compound, titanium raw material and lithium titanium raw material are mixed with a target value of Li / Ti ratio (atomic ratio) of lithium titanate, for example, 0.68 to 0.82. In accordance with a value selected from the range, both raw materials are weighed and then mixed with water or an aqueous medium of 10 to 50% by mass slurry, and then dried by heating or spray drying.
For mixing the two raw materials, a vibration mill, a ball mill or the like is appropriately used. This mixed powder remains in a bulk state or is compressed at a pressure of about 0.5 t / cm ^{2 and used} for firing as a molded body, or the mixed powder is mixed with a liquid such as water or an aqueous medium. A slurry of 50% by mass is sufficiently mixed, dried by heating or spray drying, and then compressed in the bulk or similarly to form a molded body, which is subjected to firing.

  Lithium titanate having oxygen vacancies can be obtained by performing the firing in an inert gas atmosphere or a reducing gas atmosphere. An inert gas atmosphere is a rare gas atmosphere such as argon or helium, an atmosphere such as nitrogen, or a mixed atmosphere of these gases. Reduction of oxygen, ozone, or other oxidizing gases, hydrogen, carbon monoxide, hydrogen sulfide, etc. It is an atmosphere that does not contain sex gases. The reducing gas atmosphere is a gas atmosphere such as hydrogen, carbon monoxide, or hydrogen sulfide, and may contain an inert gas. In view of environmental safety, an inert gas atmosphere is preferable, and a nitrogen gas atmosphere is more preferable.

  The firing temperature is preferably 600 to 800 ° C, more preferably 650 to 800 ° C. This heating and baking is preferably performed in two stages. For example, it is preferable that the first stage is calcined at a slightly low temperature of 600 to 700 ° C. for about 30 minutes to 5 hours, and then the second stage is fired at a higher temperature of 700 to 800 ° C. Further, the temperature rising rate during firing is preferably 5 ° C./min or less, more preferably 1 ° C./min or less. Moreover, 0.1 degreeC / min or more is preferable. Since this heating rate affects the firing time, it is preferable to set it in consideration of the balance between production efficiency and characteristics. After firing, if necessary, it may be crushed and pulverized using a hammer mill, a pin mill or the like. The lithium titanate obtained after firing in an inert gas atmosphere is obtained as blue to grayish lithium titanate, similar to lithium titanate fired in a reducing gas or in a reducing gas atmosphere.

Note that oxygen vacancies in lithium titanate can be confirmed by measuring the Ti ³⁺ concentration by electron spin resonance (ESR) spectrum. ESR observes the absorption of microwaves derived from the spin of unpaired electrons in an object to be measured. Ti in lithium titanate is usually present as Ti ⁴⁺ , but oxygen deficiency is present in lithium titanate. When Ti occurs, Ti ⁴⁺ becomes Ti ³⁺ and is compensated electronically in lithium titanate. Accordingly, since Ti ³⁺ has unpaired electrons, the presence or absence of oxygen deficiency in lithium titanate can be measured by measuring the presence of Ti ³⁺ .
In the present invention, the oxygen deficiency in the lithium titanate is preferably 1.0 × 10 ¹⁴ (pieces / g) or more as the Ti ³⁺ concentration in the ESR measurement method, and preferably 1.0 × 10 ¹⁶ (pieces). / G) or more is more preferable. Moreover, 1.0 × 10 ²² (pieces / g) or less is preferable.

This invention heat-processes the lithium titanate which has an oxygen deficiency obtained by the above methods at 400 to 600 degreeC in the atmosphere containing oxidizing gas.
Here, the oxidizing gas is oxygen, ozone, nitrous oxide, nitric oxide, nitrogen dioxide, fluorine, chlorine, chlorine dioxide, nitrogen trifluoride, chlorine trifluoride, oxygen difluoride, perchloryl fluoride. However, it is preferable to use oxygen or ozone.
These oxidizing gases may be diluted with a rare gas such as argon or helium, or an inert gas such as nitrogen or a mixed gas thereof.
The content of the oxidizing gas in the atmosphere containing the oxidizing gas is preferably 10 to 50% by volume, more preferably 15 to 35% by volume.
The atmosphere containing the oxidizing gas is preferably a mixed gas atmosphere of oxygen and nitrogen or an air atmosphere.

The heat treatment time is preferably 30 minutes to 4 hours. By performing heat treatment baking in an atmosphere containing an oxidizing gas, the blue to grayish lithium titanate becomes a slightly gray to white lithium titanate having no oxygen deficiency.
The heat-treated lithium titanate is preferably subjected to pulverization and pulverization using a hammer mill, a pin mill or the like as necessary after heating and baking.
Note that, when the ESR spectrum measurement is performed on the lithium titanate after heat treatment in an atmosphere containing an oxidizing gas, a signal derived from Ti ³⁺ is not confirmed and oxygen deficiency is eliminated.

  The furnace used for the firing or the heat treatment for obtaining lithium titanate having oxygen deficiency may be a furnace capable of adjusting the atmosphere. It can be carried out in a general box furnace, tunnel furnace, conveyor furnace, kiln furnace or the like.

  The lithium titanate obtained by the method of the present invention can be used as an active material of a lithium ion secondary battery. The lithium ion secondary battery includes a negative electrode including the lithium titanium oxide obtained by the above-described method as a negative electrode active material, a positive electrode including a positive electrode active material, and a lithium ion secondary battery including a nonaqueous electrolyte, or a negative electrode active material A positive electrode containing lithium titanium oxide obtained by the above-described method as a positive electrode active material, and a non-aqueous electrolyte. The negative electrode and the positive electrode include a current collector and an active material layer formed on the current collector, and the active material layer includes an active material, a binder, and optionally a conductive agent manufactured according to an embodiment of the present invention. May be included.

  The current collector is not particularly limited as long as it is formed of a conductive material. For example, foil, mesh, foam formed of metal such as aluminum, copper, stainless steel, nickel-plated steel, titanium, and nickel A body, a polymer coated with a conductive metal, and a combination thereof can be used.

  The binder plays a role of properly attaching the active materials to each other and further appropriately attaching the active materials to the current collector. Typical examples include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride. Ride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon and the like may be used, but are not limited thereto.

  The conductive agent is used to impart conductivity to the electrode, and in the battery that is configured, any electronic conductive material that does not cause a chemical change can be used. Natural graphite, artificial graphite, or the like may be used, and conductive materials such as polyphenylene derivatives may be mixed and used.

When the lithium titanate obtained by the method of the present invention is used as the negative electrode active material, an oxide containing lithium and a transition metal element or a polyanionic compound is used as the positive electrode active material serving as a counter electrode. Can do. Specifically, for example, lithium cobalt composite oxide [Li _(1-n) CoO ₂ etc. (0 <n <1, the same applies hereinafter)], lithium nickel composite oxide [Li _(1-n) NiO ₂ etc.] , Lithium manganese composite oxide [Li _(1-n) MnO ₂ , Li _(1-n) Mn ₂ O ₄ etc.], lithium iron composite phosphate (LiFePO ₄ etc.), lithium vanadium composite oxide (LiV ₂ O ₃ ) and the like.

  When the lithium titanate obtained by the method of the present invention is used as the positive electrode active material, the negative electrode active material serving as the counter electrode includes Li metal foil. When Li metal foil is used as the negative electrode, it can be used by directly crimping the current collector without using a conductive agent or a binder.

  As any electrode active material of the lithium ion secondary battery, lithium titanate obtained by the method of the present invention is used. The electrode of this lithium ion battery is prepared by, for example, mixing powdered lithium titanate, a conductive material and a binder, adding a suitable solvent to form a paste, and applying and drying on the surface of the current collector. In order to increase the electrode density, it can be compressed and formed. The negative electrode can be used by directly pressing the current collector without using a conductive agent or a solvent.

In the method for producing a lithium ion secondary battery of the present invention, a non-aqueous electrolyte solution, a gel electrolyte, a solid electrolyte, or the like in which a lithium salt is dissolved in a non-aqueous organic solvent can be used, but a non-aqueous electrolyte solution is used. It is preferable.
The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Examples of the non-aqueous organic solvent include ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (γ-BL), diethyl carbonate (DEC), dimethyl carbonate (DMC), butylene carbonate (BC), and ethyl methyl. Examples include organic solvents used in conventional secondary batteries and capacitors such as carbonate (EMC). These may be used alone or in combination.

Lithium salt dissolves in non-aqueous organic solvent, acts as a source of lithium ions in the battery, enables basic lithium secondary battery operation, and promotes the movement of lithium ions between the positive and negative electrodes It is a substance that performs. For example, a lithium salt such as LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , Li (CF ₃ SO ₂ ) ₂ N, Li (CF ₃ SO ₃ ), LiN (C ₂ F ₅ SO ₂ ) ₂ may be used. it can. The concentration of the lithium salt is preferably from 0.1 to 2.0M, more preferably from 0.8 to 1.2M.

  In the lithium ion secondary battery, a separator may be present between the positive electrode and the negative electrode depending on the type of the lithium ion secondary battery. The separator is not particularly limited as long as it is a material that can withstand the range of use of the lithium ion secondary battery. A thin microporous membrane can be mentioned. These may be used alone or in combination.

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.
(Example 1)
Prepare 240.9 g of lithium hydroxide as the lithium source and 573.5 g of titanium oxide powder as the titanium source, mix with ion-exchanged water so that the concentration of the raw material solids is 20% by mass, and add to this slurry As an agent, 2% by mass of Causera 2100 (manufactured by Kao Corporation) as an aqueous dispersant was added in terms of solid content.
This slurry is pulverized and mixed using a ball mill, and then spray granulated with hot air at 220 ° C. using a spray dryer (manufactured by Yamato Kagaku Co., Ltd., GB210-B) to form spherical particles having an average particle size of about 10 μm. A granulated mixed powder was obtained.

This granulated mixed powder was fired at 650 ° C. for 4 hours in a nitrogen gas atmosphere, and then fired at 800 ° C. for 4 hours to obtain a blue powdery lithium titanate. When the ESR spectrum measurement of the obtained lithium titanate was performed, a peak derived from Ti ³⁺ was detected, and Ti ³⁺ was quantified as 1.1 × 10 ¹⁹ [pieces / g]. The measurement conditions for the ESR spectrum are as follows.

Device name: Elexsys E580 (manufactured by BRUKER)
Basic measurement conditions Measurement temperature: 10K
Central magnetic field: around 3370G Magnetic field sweep range: 1000G
Modulation: 100kHz, 10G
Microwave: 4μW and 1mW
Sweep time: 167.77s x 4times
Time constant: 327.68ms
Capacity: TE ₀₁₁ , cylindrical

[Ti ³⁺ determination method]
For quantification, a standard sample with known spin number (polyethylene film into which ions were implanted) was measured under the same conditions, and was calculated by proportional calculation from the signal intensity (g value).
[Calculation of g value]
In addition, g value is a value intrinsic | native to a substance, and is calculated | required by following Formula from the microwave frequency ((nu)) and resonance magnetic field (H) which were obtained from experiment.
g = 0.71449 × ν (MHz) / H (G)

The powdered lithium titanate obtained above was heat-treated at 400 ° C. for 2 hours in an air atmosphere to produce a slightly gray powdered lithium titanate. When ESR spectrum measurement was performed again in the same manner, a peak derived from Ti ³⁺ was not detected, and oxygen deficiency could not be confirmed.
1.8 g of lithium titanate prepared by the above method was collected and dispersed in 3.0 mL of N-methyl-2-pyrrolidone, and further 0.1 g of polyvinylidene fluoride and 0.1 g of ketjen black EC600JD ( Lion Corporation) was added and mixed using a rotating / revolving vacuum mixer to make a paste.

Then, the slurry was apply | coated by the thickness of 80 micrometers on aluminum foil using the doctor blade. This was dried and then pressed and punched out together with the aluminum foil so as to form a circle having a diameter of 14.15 mm, thereby producing an electrode.
With respect to the obtained electrode, an electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio 1: 1) as an anode, A coin cell was prepared using a polypropylene nonwoven fabric as a separator.

The coin cell produced above was set in a holder installed in a constant temperature bath at 30 ° C., and charge / discharge characteristics were measured using a charge / discharge device (HJ1001SD, manufactured by Hokuto Denko).
First, a current (0.1 C) of 17.5 mA per 1 g of lithium titanate in the positive electrode was supplied to discharge the battery until the voltage reached 1.0 V, and the battery was sufficiently discharged by holding at 1.0 V for 6 hours. (Initial discharge).
After the initial discharge, the battery was charged to 3.0 V with a current of 0.1 C, and then again discharged several times to discharge to 1.0 V at 0.1 C. This cycle was repeated under the conditions of 1C, 2C, 5C, and 10C (175 mA / h, 350 mA / h, 875 mA / h, and 1750 mA / h, respectively, per 1 g of lithium titanate). The value obtained by converting the average value of the quantity into the quantity of electricity per 1 g of lithium titanate was defined as the electric capacity. As for the number of cycles at this time, only a current of 0.1 C is subjected to two cycles, and in 1C, 2C, 5C, and 10C, five cycles are performed, and the electric capacity at that time is measured. The average value of was obtained. Table 1 shows the ratio of the electric capacity at each charging current when the obtained actual value (mAh / g) and the electric capacity at 0.1 C are 100%, as charge / discharge characteristics.

(Example 2)
Powdered lithium titanate was produced under the same conditions as in Example 1 except that the heat treatment temperature was changed from 400 ° C to 500 ° C. As a result, white powdery lithium titanate was obtained. When ESR spectrum measurement was performed, no peak derived from Ti ³⁺ was detected, and oxygen deficiency could not be confirmed. Table 1 shows the results of the charge / discharge characteristics of the obtained lithium titanate.

(Example 3)
Powdered lithium titanate was produced under the same conditions as in Example 1 except that the heat treatment temperature was changed from 400 ° C to 600 ° C. As a result, white powdery lithium titanate was obtained. When ESR spectrum measurement was performed, no peak derived from Ti ³⁺ was detected, and oxygen deficiency could not be confirmed. Table 1 shows the results of the charge / discharge characteristics of the obtained lithium titanate.

(Comparative Example 1)
Powdered lithium titanate was produced under the same conditions as in Example 1 except that the firing atmosphere was changed from a nitrogen atmosphere to an air atmosphere and the second heat treatment was not performed.
As a result, white powdery lithium titanate was obtained. When ESR spectrum measurement was performed, no peak derived from Ti ³⁺ was detected, and oxygen deficiency could not be confirmed. Table 1 shows the results of the charge / discharge characteristics of the obtained lithium titanate.

(Comparative Example 2)
Powdered lithium titanate was produced under the same conditions as in Example 1 except that the firing atmosphere was changed from a nitrogen atmosphere to an air atmosphere. As a result, white powdery lithium titanate was obtained. When ESR spectrum measurement was performed, no peak derived from Ti ³⁺ was detected, and oxygen deficiency could not be confirmed. Table 1 shows the results of the charge / discharge characteristics of the obtained lithium titanate.

(Comparative Example 3)
Powdered lithium titanate was produced under the same conditions as in Example 1 except that no heat treatment was performed. As a result, blue powdery lithium titanate was obtained. Table 1 shows the results of the charge / discharge characteristics of the obtained lithium titanate.

(Comparative Example 4)
Powdered lithium titanate was produced under the same conditions as in Example 1 except that the heat treatment atmosphere was changed from an air atmosphere to a nitrogen gas atmosphere. As a result, blue powdery lithium titanate was obtained. When ESR spectrum measurement was performed, a peak derived from Ti ³⁺ was detected, and Ti ³⁺ was quantified as 0.8 × 10 ¹⁹ [pieces / g]. Table 1 shows the results of the charge / discharge characteristics of the obtained lithium titanate.

(Comparative Example 5)
Powdered lithium titanate was produced under the same conditions as in Example 1 except that the heat treatment temperature was changed from 500 ° C to 700 ° C. As a result, white powdery lithium titanate was obtained. When ESR spectrum measurement was performed, no peak derived from Ti ³⁺ was detected, and oxygen deficiency could not be confirmed. Table 1 shows the results of the charge / discharge characteristics of the obtained lithium titanate.

  From Table 1, the lithium ion secondary battery using lithium titanate obtained by the manufacturing method of the example has a charge / discharge rate of 10C and a charge / discharge rate of 85% or more at 0.1C, and at the time of high-speed charge / discharge It can be seen that this is a lithium ion secondary battery with little loss of electric capacity.

  The lithium titanate obtained by the method of the present invention has a stable crystal structure because it has no oxygen deficiency, and is useful as an electrode active material for lithium ion secondary batteries. Further, this lithium titanate is used as an electrode active material. The lithium-ion secondary battery used has little loss of electric capacity during high-speed charging / discharging and can perform stable high-speed charging / discharging, so it can be used for driving or backup of various devices such as automobiles and electronic devices, homes, offices, etc. It is useful as a secondary battery for nighttime power storage.

Claims (3)

  A method for producing lithium titanate, characterized by heat-treating lithium titanate having oxygen vacancies at 400 ° C. to 600 ° C. in an atmosphere containing an oxidizing gas.   The method for producing lithium titanate according to claim 1, wherein the lithium titanate having oxygen deficiency is fired in an inert gas atmosphere.   Titanium coated on the current collector and the current collector by applying a paint containing lithium titanate obtained according to claim 1 or claim 2, a binder, and a conductive agent on the current collector The manufacturing method of a lithium ion secondary battery including the process of producing the electrode which has a lithium acid lithium layer.