阅读说明：本技术 球形a-氧化铝阻燃剂及其制备方法 (Spherical alpha-alumina fire retardant and preparation method thereof ) 是由 龙震 沈丽丽 黄聪 王军顺 陈以檬 胡章贵 于 2019-09-20 设计创作，主要内容包括：本发明涉及一种球形a-氧化铝阻燃剂及其制备方法,由去离子水、无水乙醇、柠檬酸和三羟甲基氨基甲烷配制分散剂,将碱和铝酸盐加入到上述分散剂中形成混合溶液,反应得到超细短纤维状产物,经喷雾-烧结获得球形a-氧化铝。所述球形a-氧化铝具有粒径均匀、规则球形形貌、不含水分及高纯相的特点,并且具有更高的电子绝缘性、耐电解液腐蚀性、热稳定性,作为阻燃剂具有足够的电化学及化学稳定性、匀浆效果好。(The invention relates to a spherical alpha-alumina flame retardant and a preparation method thereof, wherein a dispersant is prepared from deionized water, absolute ethyl alcohol, citric acid and tris (hydroxymethyl) aminomethane, alkali and aluminate are added into the dispersant to form a mixed solution, a superfine short fiber-shaped product is obtained by reaction, and the spherical alpha-alumina is obtained by spraying and sintering. The spherical alpha-alumina has the characteristics of uniform particle size, regular spherical shape, no moisture and high purity phase, has higher electronic insulation, electrolyte corrosion resistance and thermal stability, has enough electrochemical and chemical stability as a flame retardant, and has good homogenization effect.)

1. A preparation method of a spherical alpha-alumina flame retardant is characterized by comprising the following steps:

preparing a dispersing agent from deionized water, absolute ethyl alcohol, citric acid and tris (hydroxymethyl) aminomethane, adding alkali and aluminate into the dispersing agent to form a mixed solution, and stirring the mixed solution until the mixed solution is in a microemulsion state, wherein the pH value is 7-7.5; the preparation proportion of each component in the dispersant is as follows: 35ml of deionized water, 2ml of absolute ethyl alcohol, 10ml of citric acid aqueous solution (the concentration is 0.1 mol/ml) and 10ml of tris aqueous solution (the concentration is 0.1 mol/ml);

step two, adding deionized water into the mixed solution for dilution, and stirring the diluted solution;

step three, spraying and drying the stirred diluted solution in spray drying equipment filled with nitrogen to obtain powder;

step four, washing the powder with deionized water, filtering, and drying;

and (V) sintering the dried powder at high temperature of 1200-1300 ℃ in a muffle furnace to obtain the product.

2. The method of claim 1, wherein: in the step (one), the stirring speed of the mixed solution is 1000 r/min.

3. The method of claim 1, wherein: in the step (one), the alkali is ammonium bicarbonate, the aluminate is one of aluminum nitrate or aluminum chloride, and the molar ratio of the alkali to the aluminate is 1: 4.

4. the method of claim 1, wherein: in the second step, the stirring speed of the diluted solution is 600 r/min.

5. The method of claim 1, wherein: in the third step, the inlet temperature of the spray drying is 150 ℃ and the outlet temperature is 80 ℃.

6. The method of claim 1, wherein: in the step (IV), the cleaning is carried out for 2 hours at the ultrasonic frequency of 100 Hz.

7. The method of claim 1, wherein: in the step (V), the sintering route is to heat up to 1200 ℃ at 10K/min, then to heat up to 500 ℃ at 1200 ℃ for 2 hours, and then to cool down to 500 ℃ at 10K/min.

8. The method of claim 1, wherein: in the step (V), the sintering route is to heat up to 1300 ℃ at 10K/min and then cool down to room temperature at 20K/min.

9. A spherical a-alumina flame retardant obtainable by the process of any one of claims 1 to 8.

10. Use of the spherical alpha-alumina flame retardant of claim 9 in a lithium ion battery separator.

Technical Field

The invention relates to the technical field of preparation of a-alumina, in particular to a high-purity spherical uniform-particle-size a-alumina flame retardant and a preparation method thereof.

Background

Since human beings are aware of energy problems and environmental problems, new clean energy is receiving much attention. The chargeable and dischargeable battery is developed to the present, the lithium sodium ion battery gradually becomes a mainstream product in the market, and according to website market statistics such as a lithium power grid, a big lithium ion battery, and a financial institution, the lithium sodium ion battery is mainly and widely applied to daily electronic equipment, new energy automobiles and large power equipment. Among them, new energy vehicles have been listed as key development projects by the nation. Under the condition of wide application, the problems of the lithium sodium ion battery are also caused, particularly, the safety accidents of the lithium battery equipment are frequent, and the safety accidents are mainly found under the conditions that the battery is collided, punctured or under the high-temperature condition in the comprehensive condition.

The Shandong Industrial ceramics research institute, published in the journal article of ceramics in 1981, shows that the inorganic diaphragm of the alkaline battery not only has good high temperature resistance and oxidation resistance, but also has high capability of blocking silver diffusion migration and resisting zinc dendrite growth and spread. The 2005 publication by Daigo Takemura et al (10.1016/j. popowour.2005.03.159) shows that ceramic powder based separators can improve separator thermal stability. Comprehensive reports show that the improvement of a lithium sodium ion battery diaphragm which mainly forms one of the core parts of the lithium sodium ion battery can improve the safety performance of the lithium battery and stabilize the application of the lithium battery, and the ceramic coating diaphragm is one of the main means for improving the performance of the diaphragm. In 2019, the latest progress of the lithium battery diaphragm in the content of the medium-star material increase and reserve plans is planned to collect 20 hundred million funds and construct a super-coating plant project.

Most studies (CN 201410542516.9, CN201811072618.3, cn201711395405. x) used alumina powder or boehmite powder for ceramic coating, commonly referred to as flame retardant. Because the aluminum oxide has physicochemical properties such as corrosion resistance, high-temperature stability and the like, particularly the a-aluminum oxide has the characteristics of structural stability, no water and the like, the ceramic coating of the a-aluminum oxide serving as the lithium battery diaphragm can solve the problems of high temperature resistance, electrolyte corrosion resistance and electronic insulativity which are not possessed by a common diaphragm, and can improve the partial safety performance of the lithium battery. According to experiments, the safety performance of the lithium battery under the collision or puncture condition can be improved by using the superfine high-purity spherical alpha-alumina as the lithium battery diaphragm flame retardant compared with the common alpha-alumina.

However, most of the aluminum oxide powders prepared by the current methods, such as a high-temperature solid phase method (CN 107032765A), a sol-gel method (CN 108863435A, CN 106430266A), a combustion method (CN 107620026A), a hydrothermal method (preparation and characterization of nano Al2O3 modified polyimide film synthesized by hydrothermal method, CN105417562A, CN 104477926A), an alkoxide method (CN 102491392A), etc., are mostly irregular in morphology, or contain certain magnetic element impurities, or have characteristics of non-uniform particle size, or high cost, etc., and thus the relationship between the particle size, morphology, purity and cost of the aluminum oxide cannot be simultaneously improved.

Disclosure of Invention

The invention aims to solve the technical problem of providing a spherical alpha-alumina flame retardant with uniform particle size and a preparation method thereof.

According to one aspect of the present invention, there is provided a method for preparing a spherical a-alumina flame retardant, comprising:

preparing a dispersing agent from deionized water, absolute ethyl alcohol, citric acid and tris (hydroxymethyl) aminomethane, adding alkali and aluminate into the dispersing agent to form a mixed solution, and stirring the mixed solution until the mixed solution is in a microemulsion state, wherein the pH value is 7-7.5; the preparation proportion of each component in the dispersant is as follows: 35ml of deionized water, 2ml of absolute ethyl alcohol, 10ml of citric acid aqueous solution (the concentration is 0.1 mol/ml) and 10ml of tris aqueous solution (the concentration is 0.1 mol/ml);

step two, adding deionized water into the mixed solution for dilution, and stirring the diluted solution;

step three, spraying and drying the stirred diluted solution in spray drying equipment filled with nitrogen to obtain powder;

step four, washing the powder with deionized water, filtering, and drying;

and (V) sintering the dried powder at high temperature of 1200-1300 ℃ in a muffle furnace to obtain the product.

Further, in the step (one), the stirring speed of the mixed solution is 1000 r/min.

Further, in the step (one), the alkali is ammonium bicarbonate, the aluminate is one of aluminum nitrate or aluminum chloride, and the molar ratio of the alkali to the aluminate is 1: 4.

further, in the step (II), the stirring speed of the diluted solution is 600 r/min.

Further, in the step (three), the inlet temperature of the spray drying was 150 ℃ and the outlet temperature was 80 ℃.

Further, in the step (IV), the cleaning is carried out by ultrasonic cleaning for 2 hours at the ultrasonic frequency of 100 Hz.

Further, in the step (V), the sintering route is to heat up to 1200 ℃ at 10K/min, then to preserve heat at 1200 ℃ for 2 hours, and then to cool down to 500 ℃ at 10K/min.

Further, in the step (V), the sintering route is to heat up to 1300 ℃ at 10K/min and then cool down to room temperature at 20K/min.

According to another aspect of the present invention, there is provided a spherical a-alumina flame retardant obtained by the above method.

In addition, the invention also claims the application of the spherical alpha-alumina flame retardant in the lithium ion battery diaphragm.

According to the invention, aluminate is used as an aluminum source, and the prepared sample can keep the shape and particle size before sintering at high temperature through the prepared dispersing agent, the regulation and control of spraying parameters and ultrasonic cleaning. Compared with other ceramic samples with uneven or larger particle size and irregular appearance, the a-alumina provided by the invention has the characteristics of uniform particle size, regular spherical appearance, no moisture and high purity phase, and has higher electronic insulation, electrolyte corrosion resistance and thermal stability.

The invention has the characteristics that the alpha-alumina serving as the flame retardant has sufficient electrochemical and chemical stability and good homogenization effect, and compared with the flame retardant prepared by other methods, the safety performance of the diaphragm under the physical environment changes such as high temperature, collision, puncture and the like can be better improved.

Drawings

FIG. 1 is an SEM image of the powder of a sample obtained by spray drying in example 1;

FIG. 2 is a graph of the powder phase of the sample obtained by spray drying +1200 ℃ sintering of example 2 compared to a standard card;

FIG. 3 is an infrared spectrum of a sample powder obtained by spray drying +1200 ℃ sintering of example 2;

FIG. 4 is an SEM image of the powder of a sample obtained by spray drying and sintering at 1200 ℃ in example 2;

FIG. 5 is an SEM image of the powder of a sample obtained by spray drying +1300 ℃ sintering of example 3.

Detailed Description

An exemplary embodiment of the present invention provides a method for preparing a spherical a-alumina flame retardant. The preparation method comprises the following steps:

step one, preparing a dispersing agent by deionized water, absolute ethyl alcohol, citric acid and tris (hydroxymethyl) aminomethane, adding alkali and aluminate into the dispersing agent to form a mixed solution, and stirring the mixed solution until the mixed solution is in a microemulsion state, wherein the pH value is 7-7.5. The preparation proportion of each component in the dispersant is as follows: 35ml of deionized water, 2ml of absolute ethyl alcohol, 10ml of an aqueous citric acid solution (concentration: 0.1 mol/ml), and 10ml of an aqueous tris (hydroxymethyl) aminomethane solution (concentration: 0.1 mol/ml). Citric acid and Tris are mainly used as buffering agents and dispersing agents. The alkali is ammonium bicarbonate. Is easy to decompose. The control is good when the spray drying is carried out. The aluminate is one of aluminum nitrate or aluminum chloride, and the molar ratio of the alkali to the aluminate is 1: 4. in specific implementation, the alkali and the aluminate are respectively added into deionized water to prepare a solution, and then the solution is slowly dropped into the prepared and stirring dispersant. The pH of the dispersant was varied from 3.5 to (7-7.5) during the addition. The stirring speed of the mixed solution is preferably 1000 r/min.

And (II) adding deionized water into the mixed solution for dilution, and stirring the diluted solution. The stirring speed of the diluted solution is preferably 600 r/min.

And (III) spray-drying the stirred diluted solution in a spray-drying device filled with nitrogen to obtain powder. The inlet temperature for spray drying was 150 ℃ and the outlet temperature was 80 ℃. The spray drying operation was carried out at a constant temperature of 26 ℃ at room temperature under aeration and drying.

And step four, washing the powder with deionized water, filtering, and drying. Ultrasonic cleaning is adopted, the ultrasonic frequency is 100 Hz, and the ultrasonic cleaning is carried out for 2 hours.

And (V) sintering the dried powder at high temperature of 1200-1300 ℃ in a muffle furnace to obtain the product. The sintering route is heating to 1200 ℃ at 10K/min, then keeping the temperature at 1200 ℃ for 2 hours, and then cooling to 500 ℃ at 10K/min. Or heating to 1300 ℃ at the speed of 10K/min, and then cooling to room temperature at the speed of 20K/min to obtain the spherical a-phase alumina flame retardant.

The method takes aluminate and alkali as raw materials, controls the grain diameter, the dispersibility and the solid content of a reaction product by adding a dispersant to obtain a superfine short fiber-shaped product, and obtains the spherical alpha-alumina by spraying and sintering. The alpha-alumina has spherical morphology, uniform particle size and high-purity alpha phase, and the alpha-alumina has no moisture.

In the method, the reaction activity and the molecular tension between reaction products are increased by adding the dispersing agent, and the particle size, the dispersibility in the solution and the solid content of the reaction products are controlled to obtain the superfine short fiber-shaped product. The appearance and the particle size of a product obtained by spray drying are controlled by combining the outlet temperature and the inlet temperature of a spraying device, the inlet speed and the nitrogen circulation, and finally the phase purity of the product is controlled by a sintering method.

The preparation method can prepare the high-purity spherical alpha alumina with uniform particle size by using the spray drying equipment and the muffle furnace equipment, and has the advantages of low cost, less electric energy consumption, safety, simple preparation process, no corrosion to used equipment and the like.

The claimed solution is further illustrated by the following examples. However, the examples are intended to illustrate embodiments of the invention without departing from the scope of the subject matter of the invention, and the scope of the invention is not limited by the examples. Unless otherwise specifically indicated, the materials and reagents used in the present invention are available from commercial products in the art.