An ultrathin sheet-like boehmite and a preparation method and application thereof

Abstract

The application provides an ultrathin sheet-shaped boehmite and a preparation method and application thereof, and the method comprises the following steps: S1, taking aluminum hydroxide aluminum raw material, and preparing a first slurry; S2, mixing the first slurry with a sodium removal agent, and then performing hydrothermal crystallization treatment to obtain an acidic aluminum hydroxide mother liquor; S3, washing and concentrating the aluminum hydroxide mother liquor through a ceramic membrane to obtain a second slurry; S4, adding a sheet forming agent into the second slurry, performing grinding, and obtaining a third slurry; and S5, performing hydrothermal crystallization treatment on the third slurry, washing the treated third slurry through a ceramic membrane, and performing spray drying to obtain a boehmite product. The method has low energy consumption, the prepared boehmite product has rhombus-like sheet-shaped crystal grains, has large particle size, thin thickness, large diameter-thickness ratio and low conductivity, and can be used for developing a more light and thin and stable performance lithium battery diaphragm coating product.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic materials, in particular to an ultrathin flaky boehmite and a preparation method and application thereof. BACKGROUND

[0002] The growth of boehmite is a dissolution and regeneration process, that is, small grains are continuously dissolved in a hydrothermal environment, deposited on large particles according to certain crystallographic directions (the growth of crystal faces is induced by elements in the growth environment), so that the grain size is continuously expanded, and finally a smooth and flat polyhedral layered structure is formed. The growth direction of flaky boehmite usually includes the growth of the length direction (end face), the width direction (side face) and the thickness direction (upper and lower surfaces). In the existing growth process of flaky boehmite, the growth behavior and speed of each crystal face of the initial grain are basically consistent, and then the growth behavior and speed of each crystal face are no longer consistent, usually the end face will experience fast, medium, slow and regrowth periods; the side face will experience fast, slow and regrowth periods; and the upper and lower surfaces will always maintain slow growth. The different growth behaviors and speeds of each crystal face in the preparation process of flaky boehmite directly affect the final morphology and size of the boehmite product.

[0003] Boehmite is widely used as a lithium battery separator coating material to improve the thermal stability of the separator, avoid short circuit between electrodes and improve the safety of lithium batteries due to its excellent insulation, chemical and electrochemical stability, flame retardance and heat resistance. In order to obtain more excellent lithium battery separator coating products, especially to obtain thinner and more stable lithium battery separator coatings, higher demands are put forward for the morphology, size and performance of boehmite materials, and there is still a large space for improvement in the existing boehmite materials and preparation methods. SUMMARY

[0004] The purpose of the present application is to provide an ultrathin flaky boehmite and a preparation method and application thereof. The boehmite product prepared by the method has a rhomboid flake-like grain shape, large particle size, thin thickness and large diameter-thickness ratio, and can be used to develop more lightweight and stable performance lithium battery separator coating products.

[0005] The technical solution adopted by the present application is as follows:

[0006] The first aspect provides a preparation method of an ultrathin flaky boehmite, comprising the following steps:

[0007] Step S1, taking aluminum hydroxide aluminum raw material, preparing a first slurry;

[0008] Step S2, mixing the first slurry with a sodium removal agent, and then performing hydrothermal crystallization treatment to obtain an acidic aluminum hydroxide mother liquor;

[0009] Step S3, washing and concentrating the aluminum hydroxide mother liquor through a ceramic membrane to obtain a second slurry;

[0010] Step S4, adding tablet-forming agents to the second slurry and performing grinding to obtain a third slurry;

[0011] Step S5, performing hydrothermal crystallization treatment on the third slurry, and then washing through a ceramic membrane and performing spray drying to obtain a boehmite product.

[0012] Preferably, in step S1, the aluminum hydroxide raw material is mixed with pure water at 50-80°C to prepare the first slurry, and the solid content in the first slurry is controlled to be 40% or higher.

[0013] Preferably, the sodium removal agent is one or more of nitric acid, sulfuric acid, acetic acid, lactic acid, oxalic acid, acrylic acid, citric acid, phosphoric acid, and stearic acid.

[0014] And / or, the tablet-forming agent is one or more of ammonium bicarbonate, potassium sulfate, acetic acid, ammonium polyacrylate, lactic acid, and sodium carbonate.

[0015] Preferably, in step S2, the temperature of the hydrothermal crystallization treatment is 140-250°C, and the time is 6-24h.

[0016] And / or, in step S5, the temperature of the hydrothermal crystallization treatment is 160-300°C, and the time is 2-24h.

[0017] Preferably, in step S3, the aluminum hydroxide mother liquor is washed through a ceramic membrane for 3-5 times, and then concentrated, with the solid content being controlled to be 55-65%.

[0018] And / or, the pH of the second slurry is controlled to be 3.5-4.5, and the conductivity is controlled to be below 100us / cm.

[0019] Preferably, in step S4, the grinding is mechanical grinding, and the tablet-forming agent is added during the grinding, with the grinding time being 0.5-5h.

[0020] Preferably, in step S5, after the hydrothermal crystallization treatment of the third slurry, the third slurry is washed through a ceramic membrane multiple times, the conductivity of the fourth slurry after washing is controlled to be 10-50us / cm, and then spray drying is performed.

[0021] The second aspect provides an ultra-thin flaky boehmite product prepared by the preparation method.

[0022] Preferably, the grain size of the boehmite product is 0.5-25μm, and the thickness is 15-500nm.

[0023] And / or, the grain size to thickness ratio of the boehmite product is 30-125.

[0024] The third aspect provides the application of the ultra-thin sheet-shaped boehmite product in lithium battery diaphragm materials, heat-conducting materials, as described in any one of the above.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] The preparation method of the application is carried out in an acidic system, so that the growth of the upper and lower crystal faces during the grain growth process is inhibited; the twice hydrothermal crystallization and washing treatment, the washing and concentration before the second hydrothermal crystallization, and the grinding treatment after mixing with the sheet-forming agent promote the growth of the grains during the second hydrothermal crystallization process, especially the growth of the end faces and the side faces of the grains, so that the boehmite product obtained finally has a thin grain thickness, a large grain size, forms an irregular sheet or a rhomboid sheet structure, has a large aspect ratio, a high dispersity, and a low conductivity. When the boehmite product prepared by the method is used as a lithium battery diaphragm coating, more layers of boehmite can be coated on the basis of the original coating thickness, the coating proportion per unit of thin film is higher, the flame retardancy and the temperature resistance can be effectively improved, and a higher energy density is obtained; and the grains of the boehmite are in an ultra-thin micrometer-level large sheet structure, which can be used to prepare a more light and thin lithium battery diaphragm coating product, the coating discharge of which is more compact, and the insulation and thermal stability are excellent; in addition, the boehmite product has a compact grain structure and a large aspect ratio, and can also be used as a heat-conducting coating, which has more excellent heat-conducting performance and flame retardancy per unit thickness. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0028] Figure 1 The preparation process flow chart of the ultra-thin sheet-shaped boehmite.

[0029] Figure 2 The scanning electron microscope picture of the boehmite product prepared in Example 1.

[0030] Figure 3 The scanning electron microscope picture of the boehmite product prepared in Example 2.

[0031] Figure 4 The scanning electron microscope picture of the boehmite product prepared in Example 3.

[0032] Figure 5 The scanning electron microscope picture of the boehmite product prepared in Example 4. DETAILED DESCRIPTION

[0033] In the following, certain exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present application. Therefore, the drawings and the description are considered to be exemplary in nature rather than limiting.

[0034] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0035] As Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 indicated, the present application provides an ultrathin flaky boehmite and a preparation method and application thereof, which is prepared according to the procedure shown in Figure 1 , using commercially available aluminum hydroxide as raw material, preparing a slurry with a certain solid content, adding an acidic desulfurizer, performing a first hydrothermal crystallization treatment in an acidic system, washing, concentrating, adding a sheet-forming agent, grinding, performing a second hydrothermal crystallization treatment in an acidic system, washing, and spray drying to obtain a boehmite product with a grain size of 0.5-25 μm, a thickness of 15-500 nm, and / or a diameter-thickness ratio of 30-125; the scanning electron microscope image of the boehmite product is shown in Figures 2 to 5 . The boehmite product has a thin grain thickness, a large grain size, an irregular flaky or rhomboid flaky structure, a large diameter-thickness ratio, a high dispersity, and a low conductivity; the boehmite is used to prepare a lithium battery separator coating product, and a more light and thin, compact, and stable quality lithium battery separator coating can be obtained.

[0036] Specifically, a preparation method of an ultrathin flaky boehmite includes the following steps:

[0037] S1, selecting aluminum hydroxide raw material (Al(OH)3) prepared by Bayer method, choline method, direct hydrolysis method, coprecipitation method, or alkoxide hydrolysis method, or selecting commercially available industrial aluminum hydroxide raw material, adding pure water at 50-80°C, and mixing for 0.5-2 h to prepare a first slurry, and controlling the solid content of the first slurry to be 40% or more, preferably controlling the solid content to be between 40-48%.

[0038] S2, adding a sodium removal agent to the first slurry prepared above, the sodium removal agent can be one or a combination of nitric acid, sulfuric acid, lactic acid, oxalic acid, acrylic acid, citric acid, phosphoric acid, and stearic acid; the amount of sodium removal agent added is controlled in the range of 0.2-0.8% by weight, after adding, the mixture is mixed thoroughly, and the mixed solution is acidic; then the acidic mixed solution is introduced into a reaction kettle, and hydrothermal crystallization treatment is carried out at 140-250°C for 6-24h, to obtain an acidic aluminum hydroxide mother liquor, and the conductivity of the aluminum hydroxide mother liquor is usually above 1000us / cm. The reaction kettle can be a hydrothermal pressure kettle or a steam steaming kettle.

[0039] S3, the obtained aluminum hydroxide mother liquor is washed multiple times by ceramic membrane, and after washing, it is concentrated to control the solid content in the range of 55-65%, and by selecting the number of washing times and the concentration ratio, the pH of the second slurry obtained is controlled in the range of 3.5-4.5, and the conductivity is below 100us / cm. The conductivity has an effect on the morphology of the product, and a high conductivity indicates a high impurity content in the mother liquor, which is not conducive to obtaining regular flaky boehmite through crystallization treatment. If the conductivity is above 500us / cm, it will lead to irregular development of boehmite, resulting in rod-shaped or needle-shaped products.

[0040] S4, adding a sheet-forming agent to the obtained second slurry, the sheet-forming agent can be one or a combination of ammonium bicarbonate, potassium sulfate, acetic acid, polyacrylammonium, lactic acid, sodium carbonate, etc., and is added by weight ratio, and the amount of addition is controlled in the range of 0.15-0.5%; mechanical grinding is used for grinding, and the sheet-forming agent is slowly added during the grinding process, and the grinding time is controlled in the range of 0.5-5h, and after grinding, a third slurry is obtained. When selecting the amount of sheet-forming agent to be added, the pH of the third slurry obtained finally should be controlled to be less than 7; mechanical grinding can be carried out by using a planetary ball mill, a sand mill, a vibration mill, or a colloid mill, etc.; adding the sheet-forming agent for grinding can effectively improve the grinding precision, make the solid content particles more uniform and the surface more smooth, which is conducive to obtaining boehmite products with more closely arranged, smoother surface, and more uniform morphology through the second hydrothermal crystallization.

[0041] S5, introducing the third slurry obtained above into a reaction kettle, and carrying out hydrothermal crystallization treatment at 160-300°C for 2-24h, and after hydrothermal crystallization treatment, the fourth slurry is washed multiple times by ceramic membrane, the conductivity of the fourth slurry after washing is controlled in the range of 10-50us / cm, and then spray drying is carried out, to obtain a boehmite product. The grain size of the boehmite product is 0.5-25μm, the thickness is 15-500nm, preferably the thickness is 15-300nm, and / or the ratio of diameter to thickness is in the range of 30-125, and the ratio of diameter to thickness is the ratio of grain size (length) to thickness. Example 1

[0042] A method for preparing ultrathin sheet-like boehmite includes the following steps:

[0043] S1, select Bayer process industrial aluminum hydroxide raw material, add it to pure water at 50-80℃, stir and mix for 1 hour to obtain the first slurry, and control its solid content at about 45%;

[0044] S2, add 0.5% oxalic acid to the first slurry, stir and mix, and then pass it into the reactor for hydrothermal crystallization treatment at 180-220℃ for 10 hours to obtain aluminum hydroxide mother liquor;

[0045] S3. The obtained aluminum hydroxide mother liquor was washed three times through a ceramic flat plate membrane. After washing, it was concentrated until the solid content was about 60% to obtain a second slurry. The pH of the second slurry was measured to be about 4.1 and the conductivity was about 85 μS / cm.

[0046] S4. Ammonium bicarbonate is slowly added to the obtained second slurry, and the mixture is ground using a planetary ball mill. The amount of ammonium bicarbonate added is controlled at 0.15%, and the grinding time is 0.5 h. The third slurry is obtained after grinding.

[0047] S5, the third slurry is introduced into the reactor and hydrothermally crystallized at 160-200℃ for 6 hours. After hydrothermal crystallization, it is washed three times through a ceramic flat plate membrane to obtain the fourth slurry, which has an electrical conductivity of about 48 μS / cm. The fourth slurry is then spray-dried to obtain the boehmite product.

[0048] The D50 grain size of this boehmite product is approximately 0.65 μm, and the D50 thickness is approximately 17 nm. Scanning electron microscopy images are shown below. Figure 2 As shown. According to Figure 2 It can be seen that the grains are in the shape of rhomboid flakes, with some grooves on the surface, and are relatively flat. Example 2

[0049] A method for preparing ultrathin sheet-like boehmite includes the following steps:

[0050] S1, select Bayer process industrial aluminum hydroxide raw material, add it to pure water at 50-80℃, stir and mix thoroughly to obtain the first slurry, and control its solid content at about 42%;

[0051] S2, add 0.4% nitric acid to the first slurry, stir and mix, and then pass it into the reactor for hydrothermal crystallization treatment at 140-200℃ for 6 hours to obtain aluminum hydroxide mother liquor;

[0052] S3. The obtained aluminum hydroxide mother liquor was washed three times through a ceramic tubular membrane. After washing, it was concentrated until the solid content was about 58% to obtain a second slurry. The pH of the second slurry was measured to be about 4.3 and the conductivity was about 81 μS / cm.

[0053] S4. Oxalic acid is slowly added to the obtained second slurry, and mechanical grinding is performed using a colloid mill. The amount of oxalic acid added is controlled at 0.5%, and the grinding time is 1 hour. The third slurry is obtained after grinding.

[0054] S5, the third slurry is introduced into the reactor and hydrothermally crystallized at 250-300℃ for 10 hours. After hydrothermal crystallization, the fourth slurry is obtained by washing three times with a ceramic tubular membrane. The conductivity of the fourth slurry is about 46 μS / cm. The fourth slurry is spray-dried to obtain boehmite product.

[0055] The D50 grain size of this boehmite product is approximately 0.81 μm, and the D50 thickness is approximately 22 nm. Scanning electron microscopy images are shown below. Figure 3 As shown. According to Figure 3 It can be seen that the grains are in the shape of rhomboid flakes, with a small number of grooves on the surface, and are relatively flat. Example 3

[0056] A method for preparing ultrathin sheet-like boehmite includes the following steps:

[0057] S1, select Bayer process industrial aluminum hydroxide raw material, add it to pure water at 50-80℃, stir and mix thoroughly to obtain the first slurry, and control its solid content at about 48%;

[0058] S2, add 0.6% lactic acid to the first slurry, stir and mix, and then pass it into the reactor for hydrothermal crystallization treatment at 200-250℃ for 16 hours to obtain aluminum hydroxide mother liquor;

[0059] S3. The obtained aluminum hydroxide mother liquor was washed four times through a ceramic tubular membrane. After washing, it was concentrated until the solid content was about 63% to obtain a second slurry. The pH of the second slurry was measured to be about 4.0 and the conductivity was about 90 μS / cm.

[0060] S4. Slowly add lactic acid to the obtained second slurry and mechanically grind it using a planetary ball mill. Control the amount of lactic acid added to be 0.3% and the grinding time to be 3 hours. After grinding, the third slurry is obtained.

[0061] S5, the third slurry is introduced into a reaction kettle, and hydrothermal crystallization treatment is carried out at 220-250 DEG C for 16h, and the fourth slurry is obtained by washing 4 times through a ceramic tubular membrane after the hydrothermal crystallization treatment; the conductivity of the fourth slurry is about 32 us / cm; the fourth slurry is subjected to spray drying to obtain a boehmite product, the D50 particle size of the crystal grains in the boehmite product is about 1.76 microns, the D50 thickness is about 33 nm, and the scanning electron microscope picture is as shown in Figure 4 It can be seen that the crystal grains are in the shape of a rhombic sheet, the structure is dense, and the surface is very smooth. Figure 4 Example 4

[0062] A method for preparing an ultra-thin sheet-shaped boehmite includes the following steps:

[0063] S1, a Bayer process industrial aluminum hydroxide raw material is selected, 50-80 DEG C pure water is added, and the mixture is fully stirred to prepare a first slurry, and the solid content is controlled to be about 48%;

[0064] S2, 0.6% of lactic acid is added to the first slurry, and the mixture is stirred and mixed, and then introduced into a reaction kettle for hydrothermal crystallization treatment at 200-250 DEG C for 22h to obtain an aluminum hydroxide mother liquor;

[0065] S3, the obtained aluminum hydroxide mother liquor is washed 3 times through a ceramic tubular membrane, and then concentrated to a solid content of about 65% to obtain a second slurry, the pH of the second slurry is about 3.8, and the conductivity is about 97 us / cm;

[0066] S4, lactic acid is slowly added to the obtained second slurry, and a planetary ball mill is used for mechanical grinding, the addition amount of lactic acid is controlled to be 0.45%, and the grinding time is 5h, and a third slurry is obtained after grinding;

[0067] S5, the third slurry is introduced into a reaction kettle, and hydrothermal crystallization treatment is carried out at 220-250 DEG C for 16h, and the fourth slurry is obtained by washing 4 times through a ceramic tubular membrane after the hydrothermal crystallization treatment; the conductivity of the fourth slurry is about 32 us / cm; the fourth slurry is subjected to spray drying to obtain a boehmite product, the D50 particle size of the crystal grains in the boehmite product is about 1.76 microns, the D50 thickness is about 33 nm, and the scanning electron microscope picture is as shown in Figure 5 It can be seen that the crystal grains are in the shape of a rhombic sheet, the structure is dense, and the surface is very smooth. Figure 5

[0068] ​​In summary, the preparation method of the present application is carried out in an acidic system, so that the growth of the upper and lower crystal faces during the grain growth process is inhibited; and after two hydrothermal crystallization and washing treatments, washing and concentration before the second hydrothermal crystallization, and mixing with tabletting agents and grinding treatment, the growth of the grains during the second hydrothermal crystallization process is promoted, especially the growth of the end faces and side faces of the grains, so that the final obtained boehmite product has thin grain thickness, large particle size, forms an irregular flake or rhomboid flake structure, and has a large aspect ratio; through two washing procedures and control of the conductivity of the slurry, the final obtained boehmite product has high dispersity and low conductivity. It is noted that the preparation method uses a preparation system with high solid content, which can significantly reduce the water consumption during the preparation process; and due to the high solid content, the volume of the reaction system is reduced, which can effectively reduce water and electricity consumption during the hydrothermal crystallization treatment, and the requirement for the size of the reaction kettle is lower.

[0069] The boehmite product prepared by the method is suitable for preparing lithium battery separator coating products; when used as a lithium battery separator coating, more layers of boehmite can be coated on the basis of the original coating thickness, the coating proportion per unit of film is higher, the flame retardancy and temperature resistance can be effectively improved, and a higher energy density can be obtained; and the grain of the boehmite is a super-thin micron-level large flake structure, which can be used to prepare a more lightweight lithium battery separator coating product, the coating discharge of which is more compact, and the insulation and thermal stability are excellent. In addition, due to the compact grain structure and large aspect ratio of the boehmite product, it can also be used as a heat-conducting coating, which has better heat-conducting performance and flame-retardant performance per unit thickness.

Claims

1. A method for preparing an ultrathin sheet-like boehmite, characterized by, The method comprises the following steps: S1, mixing aluminum hydroxide raw material with 50-80℃ pure water to prepare a first slurry; S2, mixing the first slurry with a sodium removal agent, and then performing hydrothermal crystallization treatment to obtain an acidic aluminum hydroxide mother liquor; The sodium removal agent is one or more of nitric acid, sulfuric acid, acetic acid, lactic acid, oxalic acid, acrylic acid, citric acid, phosphoric acid and stearic acid; S3, washing and concentrating the aluminum hydroxide mother liquor by ceramic membrane to obtain a second slurry; The pH of the second slurry is controlled to be 3.5-4.5, and the conductivity is below 100us / cm; S4, adding a tabletting agent to the second slurry, grinding, slowly adding the tabletting agent during the grinding process, and obtaining a third slurry; The tabletting agent is one or more of ammonium bicarbonate, potassium sulfate, acetic acid, polyacrylamide, lactic acid and sodium carbonate; The pH of the third slurry is less than 7; S5, performing hydrothermal crystallization treatment on the third slurry, washing by ceramic membrane after the treatment, and spray drying to obtain a boehmite product.

2. The method of claim 1, wherein the ultra-thin sheet-like boehmite is prepared by the steps of: In the step S1, the solid content in the first slurry is controlled to be 40% or more.

3. The method of claim 1, wherein the ultra-thin sheet-like boehmite is prepared by the steps of: In the step S2, the temperature of the hydrothermal crystallization treatment is 140-250℃, and the time is 6-24h; And / or, in the step S5, the temperature of the hydrothermal crystallization treatment is 160-300℃, and the time is 2-24h.

4. The method of claim 1, wherein the ultra-thin sheet-like boehmite is prepared by the steps of: In the step S3, the aluminum hydroxide mother liquor is washed by ceramic membrane for 3-5 times, and then concentrated, and the solid content is controlled to be 55-65%.

5. The method of claim 1, wherein the ultra-thin sheet-like boehmite is prepared by the steps of: In the step S4, the grinding is mechanical grinding, and the grinding time is 0.5-5h.

6. The method for preparing ultrathin sheet-like boehmite according to claim 1 or 3, characterized in that, In the step S5, after the hydrothermal crystallization treatment of the third slurry, the third slurry is washed by ceramic membrane for multiple times, the conductivity of the fourth slurry after washing is controlled to be 10-50us / cm, and then spray drying is performed.

7. An ultrathin sheet-like boehmite product prepared by the production method according to any one of claims 1 to 6, characterized by, The crystal grains of the boehmite product are irregular or rhomboid flake-shaped, the surface is flat, the particle size is 0.5-25μm, the thickness is 15-500nm, and the diameter-thickness ratio is 30-125.

8. The application of the ultra-thin flake-shaped boehmite product in lithium battery separator materials and heat-conducting materials according to claim 7.

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