JP2023121403A - Lithium-silicic acid stable niobic acid sol - Google Patents

Abstract

To develop niobic acid sol that has an alkaline pH of the sol and shows excellent stability.SOLUTION: A niobic acid sol contains, as a dispersion stabilizer, lithium and silicic acid. The sol preferably has a Li/Nb (molar ratio) in the range of 0.25-2.0. A suitable production method for the sol includes a first step for mixing niobic acid ammonium sol with lithium silicate and a second step for heating and/or cleaning the mixture resulting from the first step.SELECTED DRAWING: None

Description

The present invention relates to a lithium-silicic acid stable niobate sol.

In recent years, in the field of battery materials, attention has been paid to niobium-based sols as surface coating materials for positive and negative electrodes.

The present applicant invented a technology related to ammonium niobate sol described in Patent Document 1 as a niobium-based sol, and then invented an amine compound-stabilized niobate sol described in Patent Document 2. Furthermore, they have invented alkali metal-stable niobate sols described in Patent Document 3, one of which is a lithium-stable niobate sol.

Japanese Patent No. 5441264 Japanese Patent No. 6156876 Japanese Patent No. 6774158

Among niobium-based sols, there is an increasing demand for lithium-containing niobate sols.

For niobate sol with increased lithium content, when the pH of the sol becomes acidic by adding an acid that acts as a counter for lithium ions in order to maintain the stability of the sol, it is used to mix with alkaline materials. It was hard to say that it was suitable for

An object of the present invention is to develop a niobic acid sol having a neutral to alkaline pH and good stability.

As a result of intensive studies on the above problems, the present inventors surprisingly found that the above problems can be solved by using lithium and silicic acid as dispersion stabilizers, and completed the present invention based on such findings. I came to let you.

That is, the present invention is as follows.
[1] A lithium-silicic acid-stabilized niobate sol containing lithium and silicic acid as dispersion stabilizers.
[2] The lithium-silicic acid stable niobate sol according to [1] above, wherein the Li/Nb (molar ratio) is in the range of 0.25 to 2.0.
[3] (1) First step of mixing ammonium niobate sol and lithium silicate
(2) A method for producing a lithium-silicic acid-stabilized niobate sol containing lithium and silicic acid as dispersion stabilizers, comprising a second step of heating and/or washing the mixture obtained in the first step. .
[4] (1) First step of mixing ammonium niobate sol and inorganic acid
(2) Second step of washing the mixture obtained in the first step
(3) A third step of mixing the desalted gel obtained in the second step, silica sol, and a lithium compound
(4) A method for producing a lithium-silicic acid-stabilized niobate sol containing lithium and silicic acid as dispersion stabilizers, comprising a fourth step of heating and/or washing the mixture obtained in the third step. .

The present invention will be described in detail below based on preferred embodiments, but the present invention is not limited to the following embodiments, and various modifications are possible within the scope of the claims.
In the present invention, the notation "numerical value 1 to numerical value 2" regarding the numerical range means a numerical range including numerical value 1 and numerical value 2 at both ends, with numerical value 1 as the lower limit and numerical value 2 as the upper limit. It is synonymous with "numerical value 1 or more and numerical value 2 or less".

The present invention relates to a lithium-silicic acid-stabilized niobate sol (hereinafter referred to as "the sol of the present invention") containing lithium and silicic acid as dispersion stabilizers. The sol of the present invention can also be called a niobate sol stabilized with lithium and silicic acid.

In the sol of the present invention, at least a part of lithium directly binds or adsorbs to the dispersed particles of niobic acid, thereby stabilizing the dispersion of the dispersed particles in the same manner as the lithium-stabilized niobate sol described in Patent Document 3. It is thought that it contributes to On the other hand, lithium other than the above is thought to indirectly contribute to the dispersion stabilization of the dispersed particles together with coexisting silicic acid.

Li/Nb (molar ratio) in the sol of the present invention is preferably in the range of 0.25 to 2.0 (Li/Nb ₂ O ₅ (molar ratio) is in the range of 0.5 to 4.0). The lower limit of Li/Nb (molar ratio) is more preferably 0.3. Also, the upper limit of Li/Nb (molar ratio) is more preferably 1.5.

The presence of silicic acid further stabilizes the sol of the present invention, presumably because silicic acid suppresses the deposition of lithium niobate. Examples of silicic acid include water-soluble materials such as metasilicic acid and orthosilicic acid, and colloidal silica that constitutes silica sol. The silica sol is preferably a silica sol of an aqueous solvent, a so-called aqueous silica sol.

The content of silicic acid in the sol of the present invention is not particularly limited as long as it is an amount that stabilizes the sol. A suitable content range of silicic acid is preferably in the range of 0.1 to 4.0 as Si/Nb (molar ratio). More preferably, the lower limit of the above range is 0.5. Further, the upper limit of the above range is more preferably 3.0, still more preferably 2.5.

The sol of the present invention allows the inclusion of ammonia. Although the content of ammonia in the sol of the present invention is not particularly limited, it is preferably in the range of 0 or more and less than 0.5 as NH ₃ /Nb (molar ratio). The upper limit of the above range is more preferably less than 0.3, still more preferably less than 0.2. The lower limit of the above range when ammonia is contained is, for example, preferably 0.005 or more, but is preferably 0.001 or more from the viewpoint of lower content. It is believed that the ammonia in the dispersed particles when containing ammonia is bound or adsorbed to the dispersed particles at the same locations as the lithium in the dispersed particles.

The pH of the sol of the present invention is preferably in the neutral to alkaline range. In terms of pH value, it ranges from 7 to 13, for example. More preferably, it is alkaline, with a pH value in the range of, for example, 8-13.

(Production method)
The sol of the present invention is preferably produced by the following first production method or second production method. As for suitable composition ratios, etc., those described above can be applied unless otherwise specified. Moreover, the mixing method in the mixing treatment is not particularly limited, and the mixing may be performed by a conventional method.

(First manufacturing method)
The first manufacturing method includes the following first and second steps.
(1) First step of mixing ammonium niobate sol and lithium silicate
(2) A second step of heating and/or washing the mixture obtained in the first step

Ammonium niobate sol used as a raw material will be described.
Since the ammonium niobate sol and its production method are described in detail in Patent Document 1, the outline thereof will be described here. The ammonium niobate sol is a water _- dispersed sol in which fine particles of amorphous ammonium niobate are dispersed as colloidal particles. (molar ratio) = 0.25 to 0.75 (NH ₃ /Nb ₂ O ₅ (molar ratio) is 0.5 to 1.5). Ammonium niobate sol is produced by mixing and reacting an aqueous solution obtained by dissolving a niobium compound in hydrofluoric acid or a mixed acid of hydrofluoric acid and sulfuric acid with an aqueous ammonia solution while maintaining the pH at 8 or higher to produce ammonium niobate. After obtaining the dispersion liquid containing the fine particles, the dispersion liquid is filtered and washed. Further, as a commercially available ammonium niobate sol, for example, Taki Chemical Co., Ltd. trade name "Virar Nb-G6000" can be mentioned.

In the first step, ammonium niobate sol and lithium silicate are mixed. As lithium silicate, commercially available products may be used, for example, "Lithium silicate 35", "Lithium silicate 45", "Lithium silicate 75" manufactured by Nippon Kagaku Kogyo Co., Ltd., Lithium silicate liquid manufactured by Honjo Chemical Co., Ltd. etc.

In the second step, the mixture obtained in the first step is heated and/or washed. The treatment is preferably performed for the purpose of removing ammonia. For example, in the sol of the present invention, the NH ₃ /Nb (molar ratio) is less than 0.5.

The heating conditions such as temperature and time in the heat treatment may be appropriately set, but the heating temperature is preferably in the range of 50 to 150°C, for example. The lower limit of the heating temperature is more preferably 80°C, still more preferably 90°C. Moreover, the heating time may be appropriately set according to the heating temperature, and is, for example, 0.5 to 8 hours. By optimizing the amount of lithium present and the heating conditions, it is not impossible to reduce the ammonia content in the sol of the present invention to below the detection limit. In the present invention, the content below the detection limit is defined as 0. The Kjeldahl method is used to measure ammonia.

The washing method is not particularly limited, but is preferably ultrafiltration while adding water. By optimizing the washing method and washing conditions, it is not impossible to reduce the ammonia content in the sol of the present invention to below the detection limit. Either one of heating and washing may be performed, or both of them may be used. When used in combination, for example, washing may be performed after heating, or heating may be performed after washing.

The mechanism of ammonia removal by heating and/or washing treatment is presumed to be as follows. In the ammonium niobate sol, almost no ammonium ions exist, and it is presumed that ammonia exists in a state bound or adsorbed to fine particles of niobic acid, but at least part of the ammonia is replaced by lithium. As a result, free ammonia is generated, and this free ammonia is volatilized during heating and discharged out of the system during washing.

After the second step, a filtration step and a concentration adjustment step may be provided as necessary.

(Second manufacturing method)
The second manufacturing method includes the following first to fourth steps.
(1) First step of mixing ammonium niobate sol and inorganic acid
(2) Second step of washing the mixture obtained in the first step
(3) A third step of mixing the desalted gel obtained in the second step, silica sol, and a lithium compound
(4) a fourth step of heating and/or washing the mixture obtained in the third step;

The ammonium niobate sol used in the first step is the same as that described in the first production method. The amount of inorganic acid used may be appropriately set according to the desired _amount of _ammonia to be removed in the second step. be. As the amount of inorganic acid added increases, the composition tends to become gel-like. Examples of the inorganic acid include hydrochloric acid, nitric acid, sulfuric acid, etc. Of these, hydrochloric acid is particularly preferred. The method of mixing the ammonium niobate sol and the inorganic acid is not particularly limited, and the inorganic acid may be added to the ammonium niobate sol or vice versa.

The washing in the second step is not particularly limited as long as ammonia can be removed, but ultrafiltration while adding water is preferable. If the washing method and washing conditions are optimized, it is not impossible to reduce the ammonia content in the sol of the present invention to below the detection limit, but at least the NH ₃ /Nb ₂ O ₅ (molar ratio) should be less than 0.5. It is preferable to wash until the Washing enables desalting and also causes gelation, so washing in the second step yields a desalted gel.

In the third step, the desalted gel, silica sol and lithium compound are mixed. Examples of the form of silica sol and lithium compound include (i) a form in which silica sol and lithium compound are mixed, (ii) a form in which silica sol and lithium compound are mixed in advance, and (iii) a form of lithium silicate. , may be in any form.

Here, raw materials used in the (i) and (ii) modes will be described.
The silica sol is preferably an aqueous silica sol. Examples of commercially available products include the Snowtex series manufactured by Nissan Chemical Industries, Ltd., the Cataloid series manufactured by JGC Shokubai Kasei Co., Ltd., and the Silidol series manufactured by Nippon Kagaku Kogyo Co., Ltd.
Examples of lithium compounds are lithium hydroxide, lithium carbonate, lithium hydrogen carbonate and the like, preferably lithium hydroxide. Preferably, the lithium compound is an aqueous solution.

In form (i), the silica sol and the lithium compound may be mixed at the same time, but the order of silica sol and lithium compound is preferred.
In form (ii), a silica sol and a lithium compound may be simply mixed, or a mixture obtained by heating to dissolve colloidal silica may be used.
In form (iii), the same type of lithium silicate as in the first step of the first production method can be used.

As one aspect of the third step, there is an aspect in which the desalted gel and the silica sol are mixed and then heated, and then the lithium compound is added. This aspect is also included in the category of the third step. The heating in this embodiment may be carried out in the same manner as the heating in the second step of the first manufacturing method.

The heating and/or washing treatment in the fourth step may be carried out in the same manner as in the second step of the first manufacturing method.

After the fourth step, a filtration step and a concentration adjustment step may be provided as necessary.

The Nb concentration of the sol of the present invention is preferably in the range of 0.5 to 30% by mass, for example. The lower limit value is more preferably 2% by mass, still more preferably 3% by mass, and even more preferably 4% by mass, from the economical viewpoint of production and transportation. The upper limit of 30% by mass is set from the viewpoint of avoiding a drop in handleability due to an increase in viscosity. In consideration of convenience in terms of production and use, the upper limit is more preferably 20% by mass, and even more preferably 15% by mass.

When adjusting the concentration of the sol of the present invention, it may be carried out by a conventional method as long as the sol is kept stable, and examples thereof include concentration by heating, concentration under reduced pressure, and dilution with water.

The sol of the present invention can be suitably used for various purposes due to its high handleability. Examples thereof include a coating liquid for forming a transparent thin film containing the sol of the present invention, a secondary battery, an additive for electronic materials, and the like. The sol of the present invention can also be mixed with a hydrophilic solvent in preparing a coating liquid for forming a transparent thin film. Various additives such as polymer compounds such as resin emulsions, silica compounds such as silica sol and silane coupling agents, surfactants, and oxide sols having photocatalytic activity are added to the coating liquid as necessary. You may

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these.

(ammonium niobate sol)
As the ammonium niobate sol, "Viral Nb-G6000" (Nb=4.3 mass %, pH 8.8, NH ₃ /Nb (molar ratio)=0.6) manufactured by Taki Chemical Co., Ltd. was used.

[Examples 1 to 3]
To 300 g of ammonium niobate sol under stirring, "lithium silicate 35" (SiO ₂ =21.1% by mass, Li ₂ O=2.9% by mass, Si/Li (molar ratio) = 1.8) manufactured by Nippon Kagaku Kogyo Co., Ltd. or "silicic acid Lithium 45” (SiO ₂ = 21.2% by mass, Li ₂ O = 2.4% by mass, Si/Li (molar ratio) = 2.2) was added (the type of lithium silicate and the amount of each raw material added are the compositions shown in Table 1). designed to be). The resulting liquid was then heated at 90° C. for 3 hours. Finally, after filtering for the purpose of removing contaminants, the concentration was adjusted by adding an appropriate amount of water if necessary, and the material was stabilized with lithium and silicic acid containing 4.3% by mass of niobium as Nb. A niobate sol was obtained.
As in the following examples, the heating was carried out in the open, and water was added as appropriate to adjust the concentration to a predetermined level.

Table 2 shows physical properties of the obtained sol.
In addition, the sol was used for the analysis as it was, including the following analysis.
Haze, total light transmittance: Measured using a haze meter "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd. under the conditions of a wavelength of 400 to 700 nm (10 nm intervals) and an optical path length of 10 mm.

[Example 4]
After diluting 1000 g of ammonium niobate sol with deionized water to Nb ₂ O ₅ =1.0% by mass, 5% hydrochloric acid was added so that HCl/Nb ₂ O ₅ (molar ratio) = 1.5, and then ultrafiltration equipment to obtain a desalted gel. Next, Snowtex ST-C manufactured by Nissan Chemical Industries, Ltd. (hereinafter referred to as “ST-C”) was added as silica sol to the desalted gel so that Si/Nb (molar ratio)=1.0. Next, a 5% by mass lithium hydroxide aqueous solution was added so that Li/Nb (molar ratio)=1.0, and the mixture was heated at 90° C. for 3 hours. Finally, after filtering for the purpose of removing contaminants, the concentration was adjusted by adding an appropriate amount of water if necessary, and the material was stabilized with lithium and silicic acid containing 4.3% by mass of niobium as Nb. A niobate sol was obtained.

[Example 5]
In the same manner as in Example 4, except that Cataloid SN (hereinafter referred to as "SN") manufactured by JGC Shokubai Kasei Co., Ltd. was added as silica sol instead of ST-C so that Si / Nb (molar ratio) = 1.0. , a lithium- and silicic acid-stabilized niobate sol containing 4.3% by mass of niobium as Nb was obtained.

[Example 6]
After adding ST-C as silica sol to the desalted gel obtained in the same manner as in Example 4 so that Si/Nb (molar ratio)=1.0, the mixture was heated at 90° C. for 3 hours. Next, a 5% by mass lithium hydroxide aqueous solution was added so that Li/Nb (molar ratio)=1.0, and the mixture was heated at 90° C. for 3 hours. Finally, after filtering for the purpose of removing contaminants, the concentration was adjusted by adding an appropriate amount of water if necessary, and the material was stabilized with lithium and silicic acid containing 4.3% by mass of niobium as Nb. A niobate sol was obtained.

[Example 7]
Lithium and silicic acid containing 4.3% by mass of niobium as Nb in the same manner as in Example 6, except that SN was added instead of ST-C as silica sol so that Si / Nb (molar ratio) = 1.0 A stabilized niobic acid sol was obtained.

[Example 8]
Using ST-C as silica sol, add 5% by mass lithium hydroxide aqueous solution to Si/Li (molar ratio) = 1.0, heat at 50°C for 5 hours, and leave at room temperature overnight. Thus, a colorless and transparent lithium silicate aqueous solution A having a pH of 12.6 was obtained.
Lithium silicate aqueous solution A was added to the desalted gel obtained in the same manner as in Example 4 so that Si/Nb (molar ratio) = 1.0 and Li/Nb (molar ratio) = 1.0. Heated for 3 hours. Finally, after filtering for the purpose of removing contaminants, the concentration was adjusted by adding an appropriate amount of water if necessary, and the material was stabilized with lithium and silicic acid containing 4.3% by mass of niobium as Nb. A niobate sol was obtained.

[Example 9]
Using SN as a silica sol, a 5% by mass lithium hydroxide aqueous solution was added so that Si/Li (molar ratio) = 1.0, heated at 50°C for 5 hours, and left at room temperature overnight. , a colorless and transparent lithium silicate aqueous solution B having a pH of 11.3 was obtained.
In the same manner as in Example 8, except that instead of the lithium silicate aqueous solution A, the lithium silicate aqueous solution B was added so that Si/Nb (molar ratio) = 1.0 and Li/Nb (molar ratio) = 1.0. A niobate sol stabilized with lithium and silicic acid containing 4.3% by mass of niobium as Nb was obtained.

Table 3 shows the physical properties of the sols obtained in Examples 4 to 9, which were measured in the same manner as described above.

When all the sols obtained in Examples 1 to 9 were stored at 25° C. for one month, no precipitation was observed, confirming storage stability.

Claims (4)

A lithium-silicic acid-stabilized niobate sol containing lithium and silicic acid as dispersion stabilizers. 2. The lithium-silicic acid stable niobate sol according to claim 1, wherein Li/Nb (molar ratio) is in the range of 0.25 to 2.0. (1) First step of mixing ammonium niobate sol and lithium silicate
(2) A method for producing a lithium-silicic acid-stabilized niobate sol containing lithium and silicic acid as dispersion stabilizers, comprising a second step of heating and/or washing the mixture obtained in the first step. . (1) First step of mixing ammonium niobate sol and inorganic acid
(2) Second step of washing the mixture obtained in the first step
(3) A third step of mixing the desalted gel obtained in the second step, silica sol, and a lithium compound
(4) A method for producing a lithium-silicic acid-stabilized niobate sol containing lithium and silicic acid as dispersion stabilizers, comprising a fourth step of heating and/or washing the mixture obtained in the third step. .