Method for producing lithium-organic acid-stabilized niobate sol

Abstract

To develop niobic acid sol that shows excellent stability.SOLUTION: A lithium-organic acid stable niobic acid sol contains, as a dispersion stabilizer, lithium and an organic acid. The lithium-organic acid stable niobic acid sol preferably has a Li / Nb (molar ratio) in the range of 0.25-5.0. A suitable production method for the lithium-organic acid stable niobic acid sol includes a first step for mixing niobic acid ammonium sol with a lithium compound and an organic acid, and a second step for heating and / or cleaning the mixture.SELECTED DRAWING: None

Description

Technical Field

[0004] , , , , ,

[0006] , , , , , , , , , ,

[0007] , , , , , , ,

[0005]

[0001] The present invention relates to a lithium-organic acid stabilized niobate sol.

Background Art

[0002] In recent years, niobium-based sols have attracted attention as materials for surface coating of the positive and negative electrodes in the field of battery materials.

[0003] The applicant of the present application 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, an alkali metal stabilized niobate sol described in Patent Document 3 was invented, and one of them is a lithium stabilized niobate sol.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] Among niobium-based sols, the demand for niobate sols containing lithium has been increasing. In particular, a niobate sol having a higher lithium content than the lithium stabilized niobate sol described in Patent Document 3 has been demanded.

[0006] An object of the present invention is to develop a niobate sol that exhibits good stability even when the lithium content is increased.

Means for Solving the Problems

[0007] As a result of diligent research into the above-mentioned problems, the inventors of this invention surprisingly discovered that the above-mentioned problems could be solved by using lithium and organic acids as dispersion stabilizers, and based on this finding, completed the present invention.

[0008] In other words, the present invention is as follows. [1] A lithium-organic acid stabilized niobium sol containing lithium and an organic acid as dispersion stabilizers. [2] The lithium-organic acid-stable niobate sol described in [1] above, wherein the Li / Nb (molar ratio) is in the range of 0.25 to 5.0. [3] (1) First step: mixing ammonium niobate sol, lithium compound and organic acid. (2) A second step of heating and / or washing. A method for producing a lithium-organic acid-stabilized niobium sol containing lithium and an organic acid as dispersion stabilizers. [4] (1) A first step of mixing ammonium niobate sol with lithium carbonate or lithium hydroxide. (2) A second step in which the liquid obtained in the first step is heated and / or washed. (3) The third step involves performing one of the following steps (a) to (c): (a) A step of mixing the liquid obtained in the second step with an organic acid; (b) A step of mixing the liquid obtained in the second step with a lithium compound and an organic acid; (c) A step of mixing the liquid obtained in the second step with lithium carbonate. (4) A fourth step in which the liquid obtained in the third step is heated and / or washed. (5) If step (c) of the third step is carried out, the fifth step is to mix the liquid obtained in the fourth step with the organic acid. A method for producing a lithium-organic acid-stabilized niobium sol containing lithium and an organic acid as dispersion stabilizers. [Modes for carrying out the invention]

[0009] 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 this invention, the notation "value 1 to value 2" in relation to a numerical range means a numerical range that includes both values ​​1 and 2, with value 1 as the lower limit and value 2 as the upper limit, and is synonymous with "value 1 or greater and value 2 or less".

[0010] This invention relates to a lithium-organic acid-stabilized niobium sol (hereinafter referred to as "the sol of the present invention") containing lithium and an organic acid as dispersion stabilizers. The sol of the present invention can also be described as a niobium sol stabilized with lithium and an organic acid.

[0011] In the sol of the present invention, at least some of the lithium is thought to contribute to the dispersion stabilization of the dispersed particles by directly binding to or adsorbing onto the dispersed niobate particles, similar to the lithium-stable niobate sol described in Patent Document 3. On the other hand, the lithium other than that is thought to contribute indirectly to the dispersion stabilization of the dispersed particles together with the coexisting organic acid.

[0012] In the sol of the present invention, the Li / Nb (molar ratio) is preferably in the range of 0.25 to 5.0 (Li / Nb2O5 (molar ratio) is preferably in the range of 0.5 to 10.0). The lower limit of the Li / Nb (molar ratio) is more preferably 0.3 or higher.

[0013] The presence of an organic acid provides further sol stability to the sol of the present invention, which is thought to be because the organic acid suppresses the precipitation of lithium niobate. Examples of organic acids include carboxylic acids and oxycarboxylic acids. Good examples of specific compounds include acetic acid, citric acid, lactic acid, malic acid, and oxalic acid.

[0014] The content of the organic acid in the sol of the present invention is not particularly limited as long as the stabilization as a sol can be obtained. The suitable content range of the organic acid varies depending on the type of the organic acid. For example, for acetic acid, the acetic acid / Nb (molar ratio) is in the range of 0.40 to 0.60; for citric acid, the citric acid / Nb (molar ratio) is in the range of 0.30 to 5.0; for lactic acid, the lactic acid / Nb (molar ratio) is in the range of 1.0 to 10.0; for malic acid, the malic acid / Nb (molar ratio) is in the range of 0.3 to 10.0; and for oxalic acid, the oxalic acid / Nb (molar ratio) is preferably in the range of 1.0 to 3.0.

[0015] The sol of the present invention allows the inclusion of ammonia. The content of ammonia in the sol of the present invention is not particularly limited, but it is preferably in the range of 0 or more and less than 0.7 as the NH3 / Nb (molar ratio). The upper limit of the above range is more preferably less than 0.6. When containing ammonia, the lower limit of the above range is preferably 0.005 or more, for example, but from the perspective of lower content, it is preferably 0.001 or more. Ammonia in the dispersed particles when containing ammonia is considered to be bound or adsorbed to the dispersed particles at the same location as lithium in the dispersed particles.

[0016] (Manufacturing method) The sol of the present invention is preferably manufactured by the following first manufacturing method or second manufacturing method. For suitable composition ratios and the like, those described above can be applied unless otherwise particularly mentioned. Also, there is no particular limitation on the mixing method in the mixing process, and it may be mixed by a conventional method.

[0017] (First manufacturing method) The first manufacturing method includes the following first to second steps. (1) First step of mixing ammonium niobate sol, a lithium compound, and an organic acid (2) Second step of performing heating and / or washing treatment

[0018] The ammonium niobate sol used as a raw material will be described. The ammonium niobate sol and its manufacturing method are described in detail in Patent Document 1, so only an outline thereof will be described here. The ammonium niobate sol is an aqueous dispersion-type sol in which fine particles of amorphous ammonium niobate are dispersed as colloidal particles, and when the sol is dried at 100 °C for 10 hours, ammonia and niobic acid are in the range of NH3 / Nb (molar ratio) = 0.25 to 0.75 (NH3 / Nb2O5 (molar ratio) is 0.5 to 1.5). The manufacturing method of the ammonium niobate sol is to mix an aqueous solution in which a niobium compound is dissolved 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, react to obtain a dispersion containing fine particles of ammonium niobate, and then filter and wash the dispersion. Also, as a commercially available ammonium niobate sol, for example, the product named "Biral Nb-G6000" manufactured by Takaki Chemical Co., Ltd. can be cited.

[0019] In the first step, an ammonium niobate sol, a lithium compound, and an organic acid are mixed. Regarding the forms of the lithium compound and the organic acid, examples include (i) a form in which the lithium compound and the organic acid are mixed separately, (ii) a form in which the lithium compound and the organic acid are previously mixed, and (iii) a form of a lithium organic acid salt, and any form may be used.

[0020] In the (i) form, the lithium compound and the organic acid may be mixed simultaneously, but the order of the organic acid and the lithium compound is preferred. A preferred example of the lithium compound is lithium hydroxide, and preferred examples of the organic acid are citric acid, malic acid, and acetic acid.

[0021] In the (ii) form, either a solid (preferably a powder) or an aqueous solution obtained by mixing the lithium compound and the organic acid may be used. The (ii) form has the advantage that the ratio of the lithium compound and the organic acid can be arbitrarily set, unlike the (iii) form. A preferred example is an aqueous lithium citrate solution obtained by mixing an aqueous lithium hydroxide solution and citric acid.

[0022] (iii) The form may be either a solid (preferably a powder) or an aqueous solution, similar to the form in (ii). Examples of lithium organic salts in the form in (iii) include lithium citrate (Li3C6H5O7) and lithium acetate (CH3COOLi).

[0023] In the second step, the liquid obtained in the first step is heated and / or washed. This treatment is preferably performed for the purpose of removing ammonia. For example, in the sol of the present invention, this is done until the NH3 / Nb (molar ratio) is less than 0.7.

[0024] The heating conditions, including temperature and time, can be set as appropriate, but for example, the heating temperature is preferably in the range of 50 to 150°C. The lower limit of the heating temperature is more preferably 80°C, and even more preferably 90°C. The heating time can be set as appropriate according to the heating temperature, but for example, it is 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, a content below the detection limit is defined as 0. The Kjeldahl method is used to measure ammonia.

[0025] There are no particular restrictions on the washing method, but ultrafiltration with the addition of water is preferred. By optimizing the washing method and washing conditions, it is possible to reduce the ammonia content in the sol of the present invention to below the detection limit. Heating and washing may be performed individually or in combination. When used in combination, for example, washing may be performed after heating, or heating may be performed after washing.

[0026] The following is presumed to be the mechanism of ammonia removal by heating and / or washing: In ammonium niobate sol, there are almost no ammonium ions, and it is presumed that ammonia exists bound to or adsorbed onto niobate particles. At least a portion of this ammonia is replaced by lithium, thereby generating free ammonia, which is then volatilized during heating and discharged from the system during washing.

[0027] After the second step, a filtration step and a concentration adjustment step may be added as needed.

[0028] (Second manufacturing method) The second manufacturing method includes the following steps 1 to 4. If step (c) is performed in step 3, then step 5 is also included. (1) A first step of mixing ammonium niobate sol with lithium carbonate or lithium hydroxide. (2) A second step in which the liquid obtained in the first step is heated and / or washed. (3) The third step involves performing one of the following steps (a) to (c): (a) A step of mixing the liquid obtained in the second step with an organic acid; (b) A step of mixing the liquid obtained in the second step with a lithium compound and an organic acid; (c) A step of mixing the liquid obtained in the second step with lithium carbonate. (4) A fourth step in which the liquid obtained in the third step is heated and / or washed. (5) If step (c) of the third step is carried out, the fifth step is to mix the liquid obtained in the fourth step with the organic acid.

[0029] The ammonium niobate sol used in the first step is the same as that described in the first manufacturing method above.

[0030] In the first step, the mixing ratio of ammonium niobate sol to lithium carbonate or lithium hydroxide is preferably such that the Li / Nb (molar ratio) of the resulting liquid is 0.25 or higher. Regarding the upper limit of this molar ratio, if step (a) of the third step (a) to (c) is performed, it is preferably 5.0; if step (b) or (c) is performed, it is preferably 1.0, and more preferably 0.5.

[0031] The heating and / or washing processes in the second and fourth steps may be carried out in the same manner as in the second step of the first manufacturing method described above.

[0032] Good examples of organic acids in steps (a) and (b) of the third process and in step 5 are citric acid, lactic acid, malic acid, and oxalic acid.

[0033] For the lithium compound and organic acid in step (b) of the third step, the forms (i) to (iii) of the first manufacturing method described above can be applied. However, in form (i), when the organic acid and lithium compound are mixed in that order, the lithium compound is preferably lithium hydroxide, and when the lithium compound and organic acid are mixed in that order, the lithium compound is preferably lithium carbonate. Furthermore, when carrying out step (b) or step (c), it is preferable to use the lithium compound or lithium carbonate such that the Li / Nb (molar ratio) in the sol of the present invention is 5.0 or less.

[0034] The Nb concentration of the sol of the present invention is preferably in the range of 0.5 to 30% by mass. The lower limit is more preferably 2% by mass, even more preferably 3% by mass, and even more preferably 4% by mass, from an economic viewpoint of manufacturing and transportation. The upper limit of 30% by mass is set from the viewpoint of avoiding a decrease in handling performance due to high viscosity. Considering convenience in manufacturing and use, the upper limit is more preferably 20% by mass, and even more preferably 15% by mass.

[0035] When adjusting the concentration of the sol of the present invention, it may be done by conventional methods within a range that maintains the stability of the sol, such as concentration by heating, concentration under reduced pressure, or dilution with water.

[0036] The sol of the present invention has excellent handling properties and can be suitably used in a variety of applications. Examples include coating liquids for forming transparent thin films, additives for secondary batteries and electronic materials, etc., that contain the sol of the present invention. [Examples]

[0037] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

[0038] (Ammonium niobate sol) As the ammonium niobate sol, we used "Bailal Nb-G6000" manufactured by Taki Chemical Co., Ltd. (Nb = 4.3% by mass, pH 8.8, NH3 / Nb (molar ratio) = 0.6).

[0039] [Examples 1-4] To 300 g of ammonium niobate sol under stirring, an organic acid was added, followed by lithium hydroxide (the type of organic acid and the amount of each raw material added were designed to match the composition in Table 1). Next, the resulting solution was heated at 90°C for 3 hours. Finally, after filtration to remove impurities, the concentration was adjusted by adding an appropriate amount of water if necessary to obtain a lithium and organic acid-stabilized niobate sol containing 4.3% by mass of niobium (as Nb). In the following examples, as well as in other cases, heating was carried out under open conditions, and the concentration was adjusted to the desired level by adding water as needed.

[0040] [Table 1]

[0041] [Example 5] To 300 g of ammonium niobate sol under stirring, an aqueous solution prepared by pre-mixing lithium hydroxide and citric acid (citric acid / Li (molar ratio) = 0.5) was added so that the citric acid / Nb (molar ratio) was 0.5. The mixture was then heated at 90°C for 1 hour. Finally, after filtration to remove impurities, the concentration was adjusted by adding an appropriate amount of water to obtain a lithium and organic acid-stabilized niobate sol containing 4.3% by mass of niobium (as Nb) and having a Li / Nb (molar ratio) of 1.0.

[0042] [Examples 6-25] Lithium carbonate was added to 300 g of ammonium niobate sol under stirring, and the mixture was heated at 90°C for 3 hours. Next, an organic acid was added, and the mixture was heated at 90°C for 1 hour (the type of organic acid and the amount of each raw material added were designed to match the composition shown in Table 2). Finally, the mixture was filtered to remove impurities, and if necessary, the concentration was adjusted by adding an appropriate amount of water to obtain a niobate sol stabilized with lithium and an organic acid, containing 4.3% by mass of niobium (as Nb).

[0043] [Table 2]

[0044] [Example 26] To 300 g of ammonium niobate sol under stirring, lithium hydroxide was added to a mixture with a Li / Nb (molar ratio) of 0.5, and the mixture was heated at 95°C for 3 hours. Next, citric acid was added to a mixture with a citric acid / Nb (molar ratio) of 1.0, followed by the addition of lithium hydroxide. The mixture was then heated at 90°C for 3 hours. Finally, the mixture was filtered to remove impurities, and if necessary, the concentration was adjusted by adding an appropriate amount of water to obtain a lithium and organic acid-stabilized niobate sol containing 4.3% by mass of niobium (as Nb) and having a Li / Nb (molar ratio) of 1.0.

[0045] [Example 27] To 300 g of ammonium niobate sol under stirring, lithium hydroxide was added to a mixture with a Li / Nb (molar ratio) of 0.5, and the mixture was heated at 95°C for 3 hours. Next, lithium carbonate was added, followed by citric acid to a mixture with a citric acid / Nb (molar ratio) of 1.0. The mixture was then heated at 90°C for 3 hours. Finally, the mixture was filtered to remove impurities, and if necessary, the concentration was adjusted by adding an appropriate amount of water to obtain a lithium and organic acid-stabilized niobate sol containing 4.3% by mass of niobium (as Nb) and having a Li / Nb (molar ratio) of 1.0.

[0046] [Example 28] To 300 g of ammonium niobate sol under stirring, lithium hydroxide was added to achieve a Li / Nb (molar ratio) of 0.5, and the mixture was heated at 95°C for 3 hours. Next, an aqueous solution prepared by pre-mixing lithium hydroxide and citric acid (citric acid / Li (molar ratio) = 2.0) was added to achieve a citric acid / Nb (molar ratio) of 1.0, and the mixture was heated at 90°C for 1 hour. Finally, the mixture was filtered to remove impurities, and if necessary, the concentration was adjusted by adding an appropriate amount of water to obtain a lithium and organic acid-stabilized niobate sol containing 4.3% by mass of niobium (as Nb) and having a Li / Nb (molar ratio) of 1.0.

[0047] [Example 29] To 300 g of ammonium niobate sol under stirring, lithium hydroxide was added to a mixture with a Li / Nb (molar ratio) of 0.5, and the mixture was heated at 95°C for 3 hours. Next, lithium carbonate was added, and the mixture was heated at 90°C for 3 hours. Then, citric acid was added to a mixture with a citric acid / Nb (molar ratio) of 1.0. Finally, the mixture was filtered to remove impurities, and if necessary, the concentration was adjusted by adding an appropriate amount of water to obtain a lithium and organic acid-stabilized niobate sol containing 4.3% by mass of niobium (as Nb) and having a Li / Nb (molar ratio) of 1.0.

[0048] Table 3 shows the physical properties of the obtained sol. Furthermore, the sol was analyzed in its original form, including the analyses described below. • Average particle size: Measured using the "LB-500" dynamic light scattering particle size distribution analyzer manufactured by Horiba, Ltd. • Haze and total light transmittance: Measured using a haze meter "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd., under conditions of wavelength 400-700 nm (10 nm intervals) and optical path length 10 mm.

[0049] [Table 3]

[0050] In all of the sols obtained in Examples 1 to 29, no precipitate was observed when stored at 25°C for one month, confirming their storage stability.

Claims

1. (1) First step: Mixing ammonium niobate sol, lithium compound, and organic acid. (2) A second step of heating and / or washing. A method for producing a lithium-organic acid-stabilized niobium sol, comprising lithium and an organic acid as dispersion stabilizers.

2. (1) A first step of mixing ammonium niobate sol with lithium carbonate or lithium hydroxide. (2) A second step in which the liquid obtained in the first step is heated and / or washed. (3) The third step involves performing one of the following steps (a) to (c): (a) A step of mixing the liquid obtained in the second step with an organic acid; (b) A step of mixing the liquid obtained in the second step with a lithium compound and an organic acid; (c) A step of mixing the liquid obtained in the second step with lithium carbonate. (4) A fourth step in which the liquid obtained in the third step is heated and / or washed. (5) If step (c) of the third step is carried out, the fifth step is to mix the liquid obtained in the fourth step with the organic acid. A method for producing a lithium-organic acid-stabilized niobium sol, comprising lithium and an organic acid as dispersion stabilizers.

Images