JP4236100B2 - Method for producing lithium titanate fine sintered grains - Google Patents

Description

  The present invention relates to a method for producing lithium titanate fine sintered grains.

  Conventionally, a melt granulation method, a tumbling granulation method, a wet granulation method, or the like has been used for producing lithium titanate sintered particles.

  In the melt granulation method, a raw material powder containing lithium and titanium is heated and melted at about 600 ° C. in a crucible, and the melt is dripped into a refrigerant such as alcohol to form particles by rapid cooling. This is a method in which a granular material is sintered to obtain lithium titanate sintered particles.

  In the rolling granulation method, the raw material powder is mixed with a binder and placed in an inclined rotating drum, and the raw material is rolled by the rotation of the rotating drum to granulate, and the obtained granular material is sintered. Thus, lithium titanate sintered grains are obtained.

  However, in the melt granulation method, the heat melt is contaminated with impurities from the crucible during the heat melting of the raw material powder, and it is difficult to obtain high purity lithium titanate sintered grains. Since it is difficult to lower the viscosity and small droplets cannot be obtained at the time of dripping, it is very difficult to obtain lithium titanate sintered grains having a minute size of about 0.1 mm in diameter, for example.

  Further, in the rolling granulation method, since the granulation is performed by rotating the drum, not only is it difficult to obtain particles with high sphericity, but also the particle sizes of the particles are uneven, and the diameter is also 0. It is very difficult to make particles as small as about 1 mm, and it is impossible to obtain lithium titanate sintered particles having the same particle size and small size efficiently.

  Therefore, the wet granulation method is currently most used for producing lithium titanate sintered grains. In this wet granulation method, a stock solution in which a raw material powder is dispersed in an aqueous solution of a polymer resin compound is dropped from a nozzle into a bath solution that reacts with the aqueous polymer resin compound solution to gel the aqueous solution. The wet gel sphere obtained in the bath solution is dried and then sintered to obtain lithium titanate sintered grains.

  Among the wet granulation methods, for example, polyvinyl alcohol is mainly used as a polymer resin compound, and a raw solution is dropped into an acetone bath to gel the droplets (for example, see Patent Document 1). . In the wet granulation method as described above, a granular shape is formed by dropping, and a droplet formed into a particle shape by the surface tension of the stock solution during dropping is brought into contact with a liquid bath to form a polymer resin compound aqueous solution. Since the particle shape is fixed by gelling, production of lithium titanate microsintered particles having high sphericity and a uniform particle size and containing lithium titanate with high purity can be expected.

JP-A-10-265222

  In the conventional wet granulation method as described above, in order to obtain lithium titanate sintered particles having a uniform particle size and high sphericity, first, gel spheres having a uniform particle size and high sphericity are placed in a liquid bath. Must be formed with. The droplet dropped from the nozzle contacts the bath solution and undergoes a gelation reaction. First, the surface portion gels and the reaction gradually proceeds toward the center of the droplet, so that a complete gel sphere is obtained. A coagulation step is provided in which the reaction is continued by dipping in the liquid bath for a necessary time after the dropping.

  However, the droplet of the polymer resin compound aqueous solution such as polyvinyl alcohol in which the raw material powder dropped from the nozzle is dispersed has a specific gravity greater than that of acetone in the liquid bath. It may be deformed, and the settling speed in the liquid bath after dropping is fast, and if the depth of the liquid bath is not sufficient, the entire surface of the droplet reaches the bottom before gelation and accumulates here The droplets are bonded to each other, making it difficult to obtain a good gel sphere having a uniform particle size and high sphericity. Accordingly, in order to obtain a good gel sphere, it is necessary to devise facilities such as deepening the bath liquid bath or flowing down a bath liquid such as acetone.

  Further, in order to prevent the deformation of the droplet due to the impact at the time of dropping, a method of first dropping into liquid nitrogen or kerosene and then preliminarily solidifying the particles in an acetone bath solution is required. As described above, in the method of dropping into liquid nitrogen or kerosene in advance before gelation, the droplets are bonded in liquid nitrogen, and a step of removing the generated bonded particles is necessary. There was a problem that the removed material had to be treated in large quantities as waste.

  Further, in the wet granulation method, it is desired to produce a large amount of fine particles having a uniform particle diameter by using a vibration dropping means. However, as described above, liquid nitrogen or kerosene is previously used before gelation. When dripping, the vibration dripping means could not be applied.

  In view of the above problems, the object of the present invention is to provide lithium titanate micro-sintered particles having a high sphericity and a uniform particle size, while being a simple method that does not require conventional equipment. The object is to obtain a production method capable of mass production.

In order to achieve the above object, a method for producing lithium titanate fine sintered particles according to the invention described in claim 1 is a method in which a raw material powder containing lithium and titanium is dispersed in an aqueous solution of a water-soluble polymer resin compound and dropped. A stock solution preparing step for obtaining a stock solution, a droplet forming step for dropping the stock solution from a nozzle means to form droplets of the dropped stock solution, and a polymer resin compound aqueous solution that reacts upon contact with the polymer resin compound aqueous solution A solidification step of immersing the droplets in a liquid bath for gelling to form wet gel spheres in which the raw material powder is dispersedly supported; and taking out the wet gel spheres from the liquid bath A drying step for obtaining a dried gel sphere removed; a calcination step for calcining the dried gel sphere to obtain lithium titanate fine particles from which the polymer resin compound has been removed; and the lithium tie The method of manufacturing a lithium titanate fine sintered grains and a sintering step of sintering the titanate fine particles, the liquid bath is made is satisfied easily alcohols by hydration from acetone or ethanol, the stock solution adjusted step, adding an additive of the specific gravity of the dropping stock supplied to the nozzle means by reducing before dispersing to approximate liquid density of the liquid bath of the raw material powder to the water-soluble polymer resin compound solution specific gravity look including an adjustment process, the additive, the water-soluble polymer does not react with the resin compound ethanol or methanol or propanol, the content of the dropping stock at the time of adjustment end in the ratio weight adjustment process 5～60Wt% It is characterized by being within the range .

Furthermore, the manufacturing method of the lithium titanate fine sintered particles according to the invention of claim 2 is the dropping prepared in the stock solution preparation step in the method of manufacturing the lithium titanate fine sintered particles according to claim 1. The content of the polymer resin compound in the stock solution is within the range of 0.5 to 15 wt%.

  The present invention provides a specific gravity adjustment step in lithium titanate micro-sintered grains using a wet granulation method, and adds an additive to the dropping stock solution to reduce the specific gravity to approach the specific gravity of the liquid bath. Therefore, the settling speed of the droplets in which the stock solution is dropped can be suppressed, and at the same time the impact at the time of collision of the bath solution can be suppressed, so it can be dropped directly onto the gelling bath solution, and at least the entire surface of the droplets can be gelled. Since the depth of the liquid bath for securing the time required to do so can be made significantly smaller than before, lithium titanate microparticles with a uniform particle size with high sphericity can be easily obtained using a vibration dripping means. There is an effect that a large amount of sintered grains can be produced.

  In the present invention, a raw material powder containing lithium and titanium is dispersed in an aqueous solution of a polymer resin compound in a stock solution preparation step to form a dropping stock solution, and dropped in a liquid bath that gels the polymer resin compound aqueous solution in a droplet formation step Drop the undiluted solution to form a grain shape by the surface tension of the undiluted solution during the dripping, and let the droplets that have become granular in the coagulation step contact the liquid bath to gel the polymer resin compound aqueous solution, as it is It is immersed in a liquid bath only for a period of time to allow the gelation reaction to proceed to the inside of the droplets, fixing the particle shape, and obtaining wet gel spheres carrying the raw material powder in a dispersed state. A specific gravity adjusting step for adjusting the specific gravity of the stock solution is provided.

  In this specific gravity adjustment step, the specific gravity of the dripping stock solution is reduced by the addition of an additive, and approaches the liquid specific gravity of the liquid bath. As described above, in the dripping stock solution having a specific gravity close to that of the liquid in the liquid bath, the settling speed of the liquid droplets dropped in the liquid bath is slow, and the liquid droplets do not bond when they come into contact with each other. The settling distance required for the gelation of almost the entire surface of the liquid droplets is reasonably short compared to the prior art, and the required depth of the liquid bath can be set much smaller than the prior art. Furthermore, since the droplets after such dripping are collected at the bottom of the liquid bath after almost the entire surface is gelled, each particle shape is not bonded to each other at the bottom of the bath during bathing. While maintaining, the gelation reaction to the inside of the droplet proceeds.

  In addition, by adding an additive, it is also possible to impart an appropriate viscosity to the dripping stock solution, so that when it is dropped into the liquid bath, deformation of the droplet due to impact at the time of collision can be suppressed, so that the droplet is It is possible to enter the liquid bath while maintaining the highly spherical particle shape formed during the dropping, and the particle shape can be fixed by gelation.

  Therefore, according to the method of the present invention, there is no need for special equipment on the liquid bath, and other liquids such as liquid nitrogen and kerosene before being put into the liquid bath for the gelation reaction. Since it can be dropped directly into the liquid bath without requiring a dropping step into the inside, good wet gel spheres having a uniform particle size and high sphericity lithium titanate sintered particles can be obtained. Furthermore, in the present invention in which the stock solution can be dropped directly into the gelling liquid bath as described above, vibration dripping means can be used, so that a large amount of droplets having a small particle diameter can be dripped, resulting in uniform lithium titanate. It is possible to produce a large amount of fine sintered grains.

  In the specific gravity adjusting step in the present invention, if the additive is included in the stock solution preparing step, the additive is mixed with the aqueous solution of the water-soluble polymer resin compound in an addition amount that gives a predetermined content rate. The simple process of mixing the raw material powder after obtaining can be set. Of course, the present invention is not limited to such a configuration. For example, the raw material powder is mixed with the aqueous water-soluble polymer resin compound aqueous solution, and then the additive is added as the next step. And the specific gravity adjustment process may be separate processes.

  The wet gel spheres obtained by completing the gelation reaction by immersion in the liquid bath as described above are taken out of the liquid bath, and moisture is removed in the drying step to form dry gel spheres. The dried gel spheres are calcined in the calcining step to become lithium titanate calcined particles from which the polymer resin compound has been removed. Finally, the lithium titanate calcined particles are sintered in the sintering step, Nate sintered grains are obtained.

  In addition, in the formation of lithium titanate grains by the conventional wet granulation method, inexpensive polyvinyl alcohol is often used as the water-soluble polymer resin compound used in the dropping stock solution. A polymer resin compound that has been conventionally used may be used.

  Since the liquid droplets of the dripping stock solution are wet gel spheres when immersed in a liquid bath filled with a gelling agent that gels the polymer resin compound aqueous solution, as a gelling agent for the liquid bath The liquid is determined according to the type of the water-soluble polymer resin compound aqueous solution, and it is an important property that the raw material powder dispersed in the polymer resin compound does not elute. For example, acetone is mentioned when the polymer resin compound is polyvinyl alcohol as described above.

  In addition, the content of the water-soluble polymer resin compound in the dropping stock solution allows good dropping and gel formation, and at the same time, the raw material powder can be uniformly dispersed. The water-soluble polymer resin compound such as polyvinyl alcohol is preferably prepared such that the content in the dropping stock solution in the final state immediately before dropping is in the range of 0.5 to 15 wt%.

  If the content is lower than the lower limit of this range, there are too few gelling components in the droplets formed by dripping, and the gel strength is small even when gelled in contact with the liquid bath, and the sphericity is high. Spheres cannot be generated well. When the content is higher than the upper limit of the above range, the viscosity of the dropping stock solution is too high, and it becomes difficult not only to uniformly disperse the raw material powder and additives, but also the dropping itself from the nozzle becomes difficult.

  In the present invention, the additive added to reduce the specific gravity of the dripping stock solution in the specific gravity adjustment step so as to approach the liquid specific gravity of the liquid bath, and does not react with the water-soluble polymer resin compound. However, when polyvinyl alcohol is used as the water-soluble polymer resin compound and acetone is used in the liquid bath as described above, it does not react with polyvinyl alcohol, and its specific gravity is small. Suitable examples thereof include alcohols such as ethanol, methanol, and propanol.

  These alcohols such as ethanol and methanol increase the viscosity of the dropping stock solution, have high dehydration reactivity with acetone, and can further reduce the gelation time of the droplet. The dropping stock solution contains polyvinyl alcohol. It is an additive suitable when acetone is used in the liquid bath.

  The amount of the additive added is adjusted so as to obtain a specific gravity at which a gentle droplet sedimentation rate can be obtained and to obtain a viscosity capable of suppressing the deformation of the droplets. In the above alcohols such as ethanol and methanol, it is desirable that the content in the dropping stock solution in the final state immediately before dropping is in the range of 5 to 60 wt%.

  When the content is lower than the lower limit of this range, the effect of the additive cannot be sufficiently exhibited, the droplet sedimentation speed remains high, and the deformation of the droplet due to the impact at the time of the drop collision cannot be prevented. In addition, when the content is higher than the upper limit of the above range, the viscosity of the dripping stock solution becomes too high to make dripping from the nozzle difficult, and the specific gravity of the dripping stock solution becomes unnecessarily small, and the settling rate in the liquid bath Is too slow, and droplets may be combined during sedimentation.

  The temperature at which the droplets are immersed, that is, the temperature of the liquid bath is adjusted to room temperature or a temperature lower than room temperature. The temperature is preferably 25 ° C. or lower and −80 ° C. or higher. When the temperature is higher than 25 ° C., the sphericity and density of the lithium titanate micro-sintered grains are decreased, and conversely, when the temperature is lower than −80 ° C., cracking occurs when the droplet is immersed. This is because there is a problem that occurs.

  Moreover, the suitable range of the content rate in the dripping stock solution of the raw material powder containing lithium and titanium is 5 to 50 wt%. If the content of the raw material powder is lower than this range, the shrinkage when the produced wet gel spheres are dried is too large and the particle shape tends to collapse, making it difficult to obtain lithium titanate sintered particles with high sphericity. It becomes. Moreover, when the content rate is too high exceeding the above range, the viscosity of the dropping stock solution becomes too high, and dropping from the nozzle becomes difficult.

  In the droplet forming step of the present invention, the dropping stock solution is dropped from the nozzle to form a droplet, but the nozzle used can obtain a droplet of a corresponding size according to the desired lithium titanate sintered particles. What is necessary is just to select the thing of a diameter suitably.

  For dropping, a method of dropping by vibrating the nozzle at a predetermined frequency using a vibrating dropping means is simple and desirable because it can form a large amount of droplets of uniform diameter, but it is carried out by natural dropping from the nozzle. It doesn't matter.

In the case of using the vibration dropping means, it is possible to set dropping of droplets of any size by appropriately selecting the frequency. That is, when forming droplets with a vibrating nozzle, the equation Q = (π / 6) d ³ f holds, where Q is the flow rate of the dropping stock solution, d is the diameter of the droplet, and f is the frequency of the vibrating nozzle. . Therefore, the size of the droplet can be freely controlled by adjusting the flow rate Q of the dropping stock solution and the frequency f of the vibrating nozzle. When forming a droplet having a diameter d of about 0.1 mm, the flow rate Q is arbitrary, and the frequency f of the vibrating nozzle is preferably in the range of 10 to 1000 Hz.

  As an example of the present invention, a case where polyvinyl alcohol is selected as the water-soluble polymer resin compound and acetone is selected as the liquid bath to produce lithium titanate fine sintered particles will be described below. FIG. 1 is a flowchart showing the steps of this embodiment. FIG. 2 is a drawing-substituting photograph showing the appearance of the lithium titanate fine sintered particles produced according to this example.

  The manufacturing method of the lithium titanate micro-sintered particles according to this example mainly comprises a stock solution preparation step A, a droplet formation step B, a solidification step C, a drying step D, a calcination step E, and a sintering step F. Is done. In this example, the specific gravity adjustment step G is included in the stock solution preparation step A.

  In the stock solution preparation step A, first, an aqueous polyvinyl alcohol solution was prepared so that the content in the final dripping stock solution was 4 wt%. Next, as specific gravity adjusting step G, ethanol was added to the polyvinyl alcohol aqueous solution so that the content in the final dropping stock solution was 20 wt%. Using the aqueous solution of polyvinyl alcohol and ethanol as a dispersion medium, the lithium titanate raw material powder is mixed so as to have a content of 20 wt% in the final dropping stock solution. The dripping stock solution prepared as described above is supplied to the next droplet forming step B.

  In the droplet forming step B, the dropping stock solution is dropped into an acetone bath by a vibrating nozzle. As this vibration nozzle, a pump for controlling the flow rate of the dripping stock solution and a vibration mechanism for vibrating the nozzle are provided. The vibration mechanism includes an oscillator that oscillates at a frequency determined by the control means, and An amplifier that increases the frequency and a vibrator that receives the vibration amplified by the amplifier and vibrates the nozzle are used.

  In this example, a nozzle having a nozzle diameter of 1.0 mm was used, the nozzle was vibrated at a frequency of 80 Hz, and the dropping stock solution was dropped into an acetone liquid bath. By this dripping, a droplet having a diameter of about 2 mm was obtained. The liquid bath was an acetone bath filled with 3 L of acetone at a depth of 200 mm from the liquid surface. The temperature of the acetone bath was adjusted to −30 ° C.

  Subsequently, it becomes the coagulation | solidification process C from dripping of the dripping stock solution to the acetone bath. In other words, acetone is a gelling agent for an aqueous polyvinyl alcohol solution, and the liquid droplets dropped from the vibrating nozzle into the acetone bath begin to come into contact with the acetone to start gelation. While the liquid droplets settle in the acetone bath, gelation from the surface proceeds, and the droplets are immersed and held in the acetone bath until they are completely gelled.

  In this example, the drop stock solution is adjusted to have a specific gravity close to that of acetone by addition of ethanol, and is given an appropriate viscosity. The deformation due to the impact is suppressed, enters into acetone while maintaining the spherical particle shape formed during the dropping, and settles at a gentle speed. Therefore, in this embodiment, the droplets are gelled at least almost the entire surface before reaching the bottom of the acetone bath, and the droplets do not combine in a state where they are accumulated at the bottom. In this example, after dropping, the solution was kept in an acetone bath for 2 hours to complete the gelation of the droplets to obtain a lithium titanate wet gel sphere having a uniform particle size and good sphericity.

  The lithium titanate wet gel sphere is removed from the acetone bath and subjected to the drying step D. That is, the wet gel spheres are placed in a drying tank and dried at 40 ° C. for 2 hours in an air atmosphere to remove moisture from the wet gel spheres with ethanol as an additive, and to dry lithium titanate with a diameter of about 1 mm. Gel spheres were obtained.

  In the next calcination step E, the dried gel sphere obtained in the drying step D is put in a dry heat furnace and calcined at 650 ° C. for 6 hours in an air atmosphere. By this calcination, the polyvinyl alcohol in the dried gel spheres is removed by splattering to obtain lithium titanate calcination particles composed of lithium titanate.

  Further, in the sintering step F, the temperature in the dry heat furnace was raised and heated at 1100 ° C. for 1 hour. As a result, the lithium titanate calcined particles are sintered to reduce the size and become sintered particles having a high density. In this example, lithium titanate fine sintered grains having a diameter of 0.8 mm were finally obtained from droplets having a diameter of about 2 mm. As shown in the photograph of FIG. 2, the lithium titanate microsintered grains had high sphericity with a uniform grain size as a whole. The standard deviation obtained by measuring the diameter distribution of these fine sintered grains was 30 μm.

  Here, as a comparative example, a case is shown in which droplets having the same diameter are dropped with the same vibration nozzle as in this example except that ethanol is not included in the dropping stock solution. The droplets in this comparative example settle in the acetone bath at a high speed, and even when the bath has an acetone depth of 300 mm, the surface gelation of the droplets is insufficient before reaching the bottom, and the droplets at the bottom of the bath The two condensed and accumulated. Further, even when a wet gel with gelation completed at the bottom is obtained, deformation occurs due to the impact when the droplets drop and collide with the acetone liquid surface, and the shape is not a good spherical shape. It was.

  As shown in the above examples, according to the present invention, the settling rate in the gelled liquid bath of the droplets formed by adding the lithium titanate dropping stock solution by adding the additive is slow, Gelation to the extent that the droplets do not sufficiently bond at a depth of several tens of centimeters can proceed. As can be seen from the above comparative example, this is the bath depth necessary for sufficient gelation to reach the bottom. In contrast, it can be realized with a very simple equipment design.

  In addition, according to the production method of the present invention, as apparent from the above examples, since an appropriate viscosity is imparted to the dropping stock solution by the additive, at the time of liquid level collision during dropping to the liquid bath, Since deformation due to impact is suppressed and wet gel spheres with high sphericity are formed, finally, lithium titanate micro-sintered grains having a uniform particle size and high sphericity and good particle shape are formed. Can be obtained in large quantities.

  The present invention is not limited to the case where polyvinyl alcohol is used as the polymer resin compound as shown in the above examples, acetone is used as the liquid bath, and ethanol is used as the additive. Lithium titanate wet gel spheres can be obtained by dropwise addition. It is effective if an additive that can bring the specific gravity of the dropping stock solution close to the liquid bath can be selected. For example, in addition to polyvinyl alcohol, cellulose organic compounds such as methyl cellulose and ethyl cellulose can be used, and other than acetone, those that are more easily hydrated than water or ethanol can be widely used.

  In addition, the setting of conditions such as frequency, temperature, time, etc. in each step of dripping, solidification, drying, calcination, and sintering in the present invention is not limited to those shown in the above examples, but a desired particle size and quantity. It may be appropriately selected depending on the situation.

It is a flowchart figure explaining each process of the manufacturing method of the lithium titanate micro sintered grain by one Example of this invention. It is a photograph which shows the external appearance of the lithium titanate fine sintered grain obtained in the present Example.

Explanation of symbols

A: Stock solution preparation process B: Droplet formation process C: Solidification process D: Drying process E: Calcination process F: Sintering process G: Specific gravity adjustment process

Claims (2)

A stock solution preparing step of dispersing a raw material powder containing lithium and titanium in an aqueous solution of a water-soluble polymer resin compound to obtain a drop stock solution, and a droplet for dropping the stock solution from a nozzle means to form a drop of the drop stock solution A wet gel in which the raw material powder is supported in a dispersed state by immersing the droplets in a forming step and in a liquid bath that reacts upon contact with the aqueous polymer resin compound solution to gel the aqueous polymer resin compound solution A solidification step for forming spheres, a drying step for removing the wet gel spheres from the liquid bath to obtain dry gel spheres from which moisture has been removed, and preheating the dry gel spheres to remove the polymer resin compound. In the method for producing lithium titanate microsintered particles, comprising a calcining step of obtaining the lithium titanate microparticles and a sintering step of sintering the lithium titanate microparticles,
The liquid bath is filled with alcohol that is easier to hydrate than acetone or ethanol,
In the stock solution adjusting step, an additive for reducing the specific gravity of the dropping stock solution supplied to the nozzle means before the dispersion of the raw material powder to approach the liquid specific gravity of the liquid bath is added to the water-soluble polymer resin compound aqueous solution. the addition of the specific gravity adjusting step seen including,
The additive is ethanol, methanol, or propanol that does not react with the water-soluble polymer resin compound, and the content in the dropping stock solution at the end of the adjustment in the specific gravity adjustment step is in the range of 5 to 60 wt%. A method for producing lithium titanate fine sintered grains characterized by 2. The lithium titanate micro-sintered particles according to claim 1 , wherein the content of the polymer resin compound in the dropping stock solution prepared in the stock solution preparation step is in the range of 0.5 to 15 wt%. Manufacturing method.