JP5270634B2 - Method for producing lithium titanate and method for producing lithium battery - Google Patents

Description

  The present invention relates to a method for industrially producing lithium titanate, which is a useful compound for an electrode material of a lithium battery, and a lithium battery using the lithium titanate obtained by the method.

  Lithium secondary batteries have been rapidly spreading in recent years because of their high energy density and excellent charge / discharge cycle characteristics. As the lithium secondary battery, a 4V class high voltage type using lithium cobalt oxide or lithium manganate as an electrode active material is generally used. On the other hand, the circuit drive voltage of electronic devices has been decreasing, and replacement of the lithium secondary battery in the electronic device field from the high voltage type to the low voltage type has been studied. Since lithium titanate is excellent in stability and safety and is suitable for a low voltage type, development of a lithium secondary battery using this as an electrode active material is expected. By the way, the electrode of a battery is a method in which an electrode active material, a conductive material, a binder, etc. are mixed and then molded, a method in which an electrode active material, a conductive material, etc. are dispersed in a liquid medium in which the binder is dissolved, and then applied. Manufactured by. In any method, if the tap density of the electrode active material is high, the filling property is excellent and the battery capacity per unit volume of the battery can be increased. In general, the powder has a large particle size. Then, since the tap density increases, a large particle size lithium titanate is required.

  As a method for producing a large particle size lithium titanate, a slurry containing anatase-type titanium oxide and a lithium compound is spray-dried and then heated and fired so that the average particle size of secondary particles is in the range of 1 to 50 μm. A method for obtaining spherical secondary particles (see Patent Document 1), when spray-drying a slurry containing a titanate compound and a lithium compound, chlorine is added, and then heated and fired to obtain an average particle size of the secondary particles. A method of obtaining spherical secondary particles in the range of 0.5 to 100 μm (see Patent Document 2) is known.

JP 2001-192208 A (first page) JP 2002-219925 A (first page)

  In the method described in Patent Document 1, anatase-type titanium oxide is used as a titanium source. For this reason, the shrinkage rate during spray drying is small, and hollow lithium titanate secondary particles are easily generated. Tap density is not obtained. On the other hand, in the method described in Patent Literature 2, secondary particles of lithium titanate having a desired tap density can be obtained by using a titanate compound as a titanium source. In this method, the concentration of the titanate compound cannot be increased so much in terms of technical problems such as concentration and redispersion, and viscosity. In addition, since titanic acid compounds are highly reactive, the reaction proceeds partially even if they are mixed with a lithium compound at room temperature. However, if the concentration is increased, the slurry thickens and the uniform reaction is hindered, and the battery characteristics are reduced. Since excellent lithium titanate is difficult to obtain or gelation occurs and the reaction itself becomes difficult, it is necessary to react with a lithium compound at a dilute concentration, which is not suitable for mass production.

  In order to solve these problems, the present inventor has conducted extensive research and as a result, after drying and granulating a slurry containing a titanium compound and a lithium compound, the method of producing lithium titanate by heating and firing, When a slurry containing crystalline titanium oxide and a titanic acid compound is used as the titanium compound and the slurry is prepared at a temperature lower than 45 ° C., the concentration of the titanium source can be increased, and this is an industrially advantageous method. In addition, the lithium titanate obtained by drying and granulating the prepared slurry, followed by heating and firing was found to have a high tap density and excellent fillability, and the present invention was completed.

  That is, the present invention relates to a method for producing lithium titanate by drying and granulating a slurry containing a titanium compound and a lithium compound, followed by heating and firing, and containing crystalline titanium oxide and a titanate compound as the titanium compound. And the slurry is prepared at a temperature lower than 45 ° C.

  INDUSTRIAL APPLICABILITY The present invention can industrially advantageously produce lithium titanate having high filling properties and excellent battery characteristics. When this lithium titanate is used as an electrode active material, a lithium battery having excellent battery characteristics can be obtained.

The present invention is a method for producing lithium titanate, in which a slurry containing a titanium compound and a lithium compound is dried and granulated and then heated and fired to produce lithium titanate. A slurry containing a titanic acid compound is used, and the slurry is prepared at a temperature lower than 45 ° C. According to the present invention, the concentration of the titanium component can be increased even in a slurry containing a lithium compound, and even when crystalline titanium oxide is used as a titanium source, secondary particles having high tap density, excellent filling properties, and excellent battery characteristics. The lithium titanate consisting of can be industrially advantageously produced. For example, in a method in which a titanic acid compound and a lithium compound are mixed in a slurry, the concentration of the titanium component can only be up to 60 g / liter in terms of TiO ₂ , but in the present invention, crystalline titanium oxide and titanium are used as the titanium compound. By using one containing an acid compound, the total concentration of titanium components can be in the range of 70 to 300 g / liter, preferably 100 to 250 g / liter in terms of TiO ₂ .

  In the present invention, first, in preparing a slurry containing a titanium compound and a lithium compound, a slurry containing crystalline titanium oxide and a titanic acid compound is used as the titanium compound, and the slurry is prepared at a temperature lower than 45 ° C. (First step). Water or an organic solvent such as alcohol, or a mixture thereof can be used for the liquid medium used for slurrying, but there is no particular limitation, but it is preferable industrially to use water. The order of addition of the lithium compound, titanic acid compound and crystalline titanium oxide is such that the titanic acid compound is added to the slurry containing the lithium compound and crystalline titanium oxide, or the slurry is added in parallel to the slurry containing the lithium compound. It is preferable to add the titanic acid compound and the crystalline titanium oxide at the same time, for example, by adding them as a mixture because thickening and gelation are less likely to occur and the concentration of the titanium source is easily increased. When the amount of crystalline titanium oxide added is equal to or greater than the titanic acid compound by weight, lithium titanate can be produced industrially advantageously. If the amount added is larger than 4 times, it is difficult to obtain lithium titanate having a large tap density, and it is difficult to obtain lithium titanate having a uniform composition unless fired at a high temperature. Therefore, it is preferable to make the amount 4 times as much as possible. When the slurry is adjusted at a temperature lower than 45 ° C., the reaction between the lithium compound and the titanate compound is difficult to proceed. Therefore, it is more preferable that the slurry has an appropriate viscosity and is kept at room temperature or lower.

  The lithium compound used in the present invention is not particularly limited, but when preparing a slurry using water or an aqueous medium containing water as a main component, a water solution such as lithium hydroxide, lithium carbonate, lithium nitrate, or lithium sulfate is used. It is preferable to use a reactive lithium compound, and it is particularly preferable to use lithium hydroxide having high reactivity.

The titanate compound, TiO _{(OH) 2} or metatitanic acid represented by _{TiO 2 · H 2 O, Ti} (OH) 4 or orthotitanate represented by _{TiO 2} · 2H 2 O, or a mixture thereof Can be used. A titanic acid compound is obtained by heat hydrolysis or neutralization hydrolysis of a titanium compound. For example, metatitanic acid is obtained by heating hydrolysis of titanyl sulfate (TiOSO ₄ ), neutralization hydrolysis of titanium chloride at a high temperature, etc. Titanic acid is neutralized hydrolysis of titanium sulfate (Ti (SO ₄ ) ₂ ) and titanium chloride at low temperatures, and a mixture of metatitanic acid and orthotitanic acid appropriately controls the neutralized hydrolysis temperature of titanium chloride. Can be obtained. If an ammonium compound such as ammonia, ammonium carbonate, ammonium sulfate, or ammonium nitrate is used as the neutralizing agent for neutralization hydrolysis, it can be decomposed and volatilized during firing. In addition to the inorganic compounds such as titanium sulfate, titanyl sulfate, and titanium chloride, organic compounds such as titanium alkoxide may be used as the titanium compound.

It is preferable to use crystalline titanium oxide having an average particle diameter of 0.01 to 0.4 μm because the viscosity of the slurry is hardly increased even when the concentration is high. The crystalline titanium oxide is a titanium oxide represented by TiO ₂ and having an anatase type, rutile type or brookite type crystal structure. In the present invention, the X-ray diffraction pattern has a plurality of crystal structures such as a crystalline titanium oxide having only a diffraction peak from a single crystal structure, as well as an anatase type diffraction peak and a rutile type diffraction peak. It may have a diffraction peak from. Moreover, a part of the amorphous material that does not appear in the X-ray diffraction pattern may be included.

  The slurry obtained in the first step is dried and granulated and then heated and fired to obtain lithium titanate. There is no limitation on the method of dry granulation. For example, the solid content is separated from the slurry by solid-liquid separation, dried, pulverized, and granulated into secondary particles of a desired size, and the slurry is spray-dried. And a method of granulating into secondary particles. In particular, a method using spray drying is preferable because the particle diameter can be easily controlled and spherical secondary particles can be easily obtained. When spray drying is applied, the viscosity of the slurry may be adjusted by dilution depending on the ability of the spray dryer used. In the present invention, when the slurry obtained in the first step is wet-heat treated, it is preferable because the viscosity is reduced and spray drying can be performed at a high concentration even after cooling to room temperature. When the wet heating temperature is at least 50 ° C., the slurry viscosity becomes moderate and the effect of the present invention is easily obtained, and is preferably 100 ° C. or less because special equipment such as a pressure vessel is not required. More preferably, the temperature is in the range of -100 ° C.

  The spray dryer used for spray drying can be appropriately selected according to the properties and processing capacity of the slurry, such as a disk type, a pressure nozzle type, and a two-fluid nozzle type. The control of the secondary particle size is, for example, by adjusting the number of rotations of the disk in the case of the above-mentioned disk type, and adjusting the spray pressure and the nozzle diameter in the case of a pressure nozzle type or a two-fluid nozzle type, etc. This can be done by controlling. In order to make it easier to control the particle size, various additives such as binders such as polyvinyl alcohol, methylcellulose, and gelatin, and nonionic, anionic, amphoteric, and nonionic surfactants may be used. These additives are desirable if they are organic and do not contain a metal component, because they are decomposed and volatilized in a later heating and firing step. As the drying temperature, the inlet temperature is preferably in the range of 200 to 450 ° C, and the outlet temperature is preferably in the range of 80 to 120 ° C.

  The firing temperature varies depending on the firing atmosphere, but in the present invention, it may be approximately 600 ° C. or higher in order to produce lithium titanate, and 1000 ° C. or lower in order to prevent sintering between secondary particles. preferable. A more preferable heating and baking temperature is 650 to 850 ° C, and further preferably 700 to 800 ° C. If the obtained lithium titanate secondary particles are sintered and agglomerated after heating and firing, they may be pulverized using a flake crusher, a hammer mill, a pin mill or the like, if necessary.

Since the lithium titanate obtained in the present invention has a large particle diameter (50% median diameter by laser scattering method) in which secondary particles are in the range of 1 to 100 μm, the tap density is 1.0 to 2.5 g / cm ^3. The range is preferably as large as 1.2 to 2.0 g / cm ³ , and the filling property is excellent. The secondary particles in the present invention are in a state in which the primary particles are firmly bonded to each other, and are not aggregated or mechanically consolidated by interaction between particles such as van der Waals force, In ordinary mechanical pulverization used in the above, it is not easily disintegrated and most of it remains as secondary particles. The shape of the secondary particles is not particularly limited, such as a spherical shape, a polyhedral shape, and an irregular shape, but a shape having as little anisotropy as possible is advantageous in terms of battery characteristics, and a spherical shape is more preferable. The shape of each primary particle constituting the secondary particle is not particularly limited, such as a spherical shape, a polyhedral shape, and an indefinite shape. The composition of the primary particles is represented by the general formula Li _x Ti _y O ₄ and is preferably a single phase of lithium titanate, but even if some titanium oxide is mixed within a range not impairing the effects of the present invention. Good. The values of x and y in the general formula are preferably in the range of 0.5 to 2 in terms of x / y values.

Next, the present invention is a lithium battery, wherein the lithium titanate obtained by the above method is used as an electrode active material. The electrode for a lithium battery is obtained by adding a conductive material such as carbon black and a binder such as a fluororesin to lithium titanate, and appropriately molding or applying it. The lithium battery is composed of the electrode, the counter electrode, and the electrolytic solution. When lithium titanate is used for the positive electrode, metal lithium, lithium alloy, or a carbon-based material such as graphite or coke is used as the counter electrode. In addition, lithium-containing manganese oxide, lithium manganate, lithium cobaltate, lithium nickelate, vanadium pentoxide, or the like is used as a counter electrode when lithium titanate is used as the negative electrode. In the electrolytic solution, lithium salts such as LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ were dissolved in a solvent such as propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane. Conventional materials such as those can be used.

  Examples of the present invention are shown below, but these do not limit the present invention.

Reference example 1
(1) Preparation of slurry 371 g of crystalline titanium oxide (having anatase type and rutile type diffraction peaks) was added and dispersed in 1151 ml of a 4.9 mol / liter lithium hydroxide aqueous solution. While stirring this slurry (a), 1195 ml of slurry (b) in which titanic acid compound (ortho titanic acid) was dispersed in pure water so as to have a concentration of 155 g / liter in terms of TiO ₂ was added, A slurry (c) containing a lithium compound, a titanic acid compound and crystalline titanium oxide powder was obtained. The total concentration of titanium components in the slurry (c) was 230 g / liter in terms of TiO ₂ .

(2) Preparation of dried granulated product 500 ml of pure water was added to the slurry (c) to adjust the viscosity to 750 mPa · s. The total concentration of titanium components at this time was 190 g / liter in terms of TiO ₂ . This slurry was spray-dried under conditions of an inlet temperature of 250 ° C. and an outlet temperature of 110 ° C. using a mobile minor type spray dryer (manufactured by Niro Co., Ltd.) to obtain a dried granulated product.

(3) Heating and firing of dried granulated product The obtained dried granulated product was heated and fired in the atmosphere at a temperature of 750 ° C. for 3 hours to obtain a lithium oxide lithium oxide (sample A) as a reference example .

Reference example 2
In the preparation of the slurry (c), the amount of crystalline titanium oxide added was 278 g, the amount of titanic acid compound aqueous slurry (b) was 1794 ml, and the amount of pure water added before spray drying was 1000 ml. In the same manner as in Reference Example 1 , lithium titanate (Sample B) was obtained. The total concentration of titanium components before spray drying was 139 g / liter in terms of TiO ₂ , and the viscosity of the slurry was 960 mPa · s.

Reference example 3
In the preparation of the slurry (c), except that the amount of crystalline titanium oxide added was 445 g, the amount of titanic acid compound aqueous slurry (b) was 718 ml, and the amount of pure water added before spray drying was 550 ml, In the same manner as in Reference Example 1 , lithium titanate (Sample C) was obtained. The total concentration of the titanium component prior to spray drying at 220 g / l in terms of TiO _2, the slurry viscosity was 800 mPa · s.

Example 1
The lithium titanate (sample D) was prepared in the same manner as in Reference Example 1 except that the slurry (c) prepared in the same manner as in Reference Example 1 was not diluted, heat-treated at a temperature of 80 ° C., and then cooled to room temperature. Obtained. The viscosity of the slurry cooled to room temperature was 105 mPa · s.

Reference example 4
(1) Preparation of slurry
To a slurry (d) in which 371 g of crystalline titanium oxide used in Reference Example 1 was dispersed in 1550 ml of pure water, 237 g of lithium hydroxide monohydrate powder was added. The slurry was stirred, and 1195 ml of the titanate slurry (b) used in Reference Example 1 was added to obtain a slurry (e). The total concentration of the titanium components in the slurry (e) was 196 g / liter in terms of TiO ₂ .

(2) Preparation of dried granulated product and heating and firing thereof 650 ml of pure water was added to the slurry (e) to adjust the viscosity to 1050 mPa · s. The total concentration of titanium components at this time was 160 g / liter in terms of TiO ₂ . A dry granulated product was prepared from this slurry in the same manner as in Reference Example 1, and heated and fired to obtain lithium titanate (Sample E).

Reference Example 5
(1) Preparation of slurry
371 g of the crystalline titanium oxide used in Reference Example 1 was added to 1684 ml of slurry (f) in which the titanate compound used in Reference Example 1 was dispersed in pure water so as to have a concentration of 110 g / liter in terms of TiO _2. This was added to prepare a mixed slurry (g) of titanic acid compound and crystalline titanium oxide. 1151 ml of a 4.9 mol / liter lithium hydroxide aqueous solution was stirred, and slurry (g) was added thereto to obtain slurry (h). The total concentration of titanium components in the slurry (h) was 190 g / liter in terms of TiO ₂ .

(2) Preparation of dried granulated product and heating and firing thereof 300 ml of pure water was added to the slurry (h) to adjust the viscosity to 880 mPa · s. The total concentration of titanium components at this time was 172 g / liter in terms of TiO ₂ . A dry granulated material was prepared from this slurry in the same manner as in Reference Example 1, and heated and fired to obtain lithium titanate (Sample F).

Comparative Example 1
Stirring 1,527 ml of a 2.46 mol / liter lithium hydroxide aqueous solution, and adding 371 g of crystalline titanium oxide used in Reference Example 1 . The slurry containing lithium hydroxide and crystalline titanium oxide was granulated and heated and fired in the same manner as in Reference Example 1 without dilution to obtain a comparative sample lithium titanate (sample G). The concentration of crystalline titanium oxide in the slurry was 230 g / liter in terms of TiO ₂ , and the slurry viscosity was 530 mPs · s.

Comparative Example 2
In the preparation of the slurry (c) of Reference Example 1 , an attempt was made to add a total of 3585 milliliters of the slurry (b) of the titanate compound without adding crystalline titanium oxide. could not.

Evaluation 1: Measurement of secondary particle diameter The aqueous slurry of lithium titanate (samples A to G) obtained in Example 1, Reference Examples 1 to 5 and Comparative Example 1 was sufficiently ultrasonically dispersed and transmitted by laser light. After adjusting the rate to 85 ± 1%, the average particle diameter was measured as the median diameter on a volume basis using a laser diffraction / scattering particle size distribution measuring device (LA-910: manufactured by Horiba, Ltd.).

Evaluation 2: Measurement of tap density 50 g of the lithium titanate (samples A to G) obtained in Example 1 , Reference Examples 1 to 5 and Comparative Example 1 was put into a 100 ml measuring cylinder and tapped 100 times. The tap density was measured.

Evaluation 3: Measurement of battery characteristics The charge / discharge characteristics of the lithium secondary battery in the case where the lithium titanate (samples A to G) obtained in Example 1 , Reference Examples 1 to 5 and Comparative Example 1 was used as an electrode active material. evaluated. The battery configuration and measurement conditions will be described.

  The above samples, graphite powder as a conductive agent, and polytetrafluoroethylene resin as a binder are mixed at a weight ratio of 5: 4: 1, kneaded in a mortar, molded into a 10 mm diameter circle, and pellets It was in the shape. The weight of the pellet was 20 mg. An aluminum mesh cut to a diameter of 10 mm was superimposed on this pellet and pressed at 14.7 MPa to obtain a working electrode.

This working electrode was vacuum-dried at 120 ° C. for 4 hours, and then incorporated in a sealable coin-type evaluation cell in a glove box having a dew point of −70 ° C. or lower. The evaluation cell used was made of stainless steel (SUS316) and had an outer diameter of 20 mm and a height of 1.6 mm. As the counter electrode, a metal lithium having a thickness of 0.5 mm formed into a circle having a diameter of 14 mm was used. As the non-aqueous electrolyte, a mixed solution of ethylene carbonate and dimethyl carbonate (mixed in a volume ratio of 1: 2) in which LiPF ₆ was dissolved at a concentration of 1 mol / liter was used.

  The working electrode was placed in the lower can of the evaluation cell, a porous polypropylene film was placed thereon as a separator, and 7 drops of nonaqueous electrolyte were dropped from above with a dropoid. Further, a negative electrode was placed thereon, and an upper can with a propylene gasket was placed thereon, and the outer peripheral edge was caulked and sealed.

  The charge / discharge capacity was measured at a constant current with the voltage range set to 1 V to 2 V and the charge / discharge current set to 0.4 mA (about 3 cycles / day).

Evaluation 4: Measurement of specific surface area Specific surface area of the lithium titanate (samples A to G) obtained in Example 1, Reference Examples 1 to 5 and Comparative Example 1 was measured using a specific surface area measuring device (Monosorb: manufactured by Yuasa Ionics ). Was measured by the BET method.

Table 1 shows the average particle size, tap density, discharge capacity, and specific surface area of Samples A to G. It can be seen that the lithium titanate of the present invention has a large particle size, excellent filling properties, and high discharge capacity. Moreover, the lithium titanate obtained in the present invention has a composition in which x / y is about 0.8 in the formula: Li _x Ti _y O ₄ .

  The lithium titanate obtained in the present invention is useful for a high capacity lithium battery.

Claims (4)

In a method for producing lithium titanate by drying and granulating a slurry containing a titanium compound and a lithium compound, and then heating and firing to produce lithium titanate, crystalline titanium oxide and titanic acid compound are used as the titanium compound, and crystalline titanium oxide is converted to titanic acid. A compound containing 1 to 4 times the weight ratio in terms of TiO ₂ with respect to the compound was used, and after the slurry was prepared at a temperature lower than 45 ° C, the slurry was wet at a temperature of at least 50 ° C. A method for producing lithium titanate, which is subjected to a heat treatment and then subjected to a dry granulation step without dilution at room temperature.
Tap density is 1.0-2.5 g / cm ³ The method for producing lithium titanate according to claim 1, wherein lithium titanate in the range is obtained. 2. The method for producing lithium titanate according to claim 1, wherein the dry granulation is performed by spray drying. A step of obtaining lithium titanate by the method according to claim 1, a step of forming or applying a conductive agent and a binder to the lithium titanate to obtain an electrode, a step of forming a lithium battery using the electrode, counter electrode and electrolyte A method for producing a lithium battery, comprising: