Lithium-silicate stabilized niobate sol

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

[Technical Field]

[0001] The present invention relates to a lithium-silicate stabilized niobic acid sol. [Background technology]

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

[0003] The present applicant first invented a technology relating to ammonium niobate sol as a niobium-based sol, as described in Patent Document 1, and then invented an amine compound-stabilized niobic acid sol, as described in Patent Document 2. Furthermore, he invented alkali metal-stabilized niobic acid sols, as described in Patent Document 3, one of which is a lithium-stabilized niobic acid sol. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5441264 [Patent Document 2] Patent No. 6156876 [Patent Document 3] Patent No. 6774158 Summary of the Invention [Problem to be solved by the invention]

[0005] Among niobium-based sols, there is an increasing demand for lithium-containing niobic acid sols.

[0006] In a niobic acid sol with an increased lithium content, if an acid that acts as a counter to the lithium ions is added to maintain the stability of the sol, the pH of the sol becomes acidic, making it unsuitable for mixing with alkaline materials.

[0007] An object of the present invention is to develop a niobic acid sol whose pH is neutral to alkaline and which exhibits good stability. [Means for solving the problem]

[0008] As a result of extensive research into the above-mentioned problems, the present inventors have surprisingly found that the above-mentioned problems can be solved by using lithium and silicic acid as a dispersion stabilizer, and have completed the present invention based on this finding.

[0009] That is, the present invention is as follows. [1] A lithium-silicate stabilized niobic acid sol containing lithium and silicic acid as dispersion stabilizers. [2] The lithium-silicate stabilized niobate sol according to the above [1], 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 second step in which the mixture obtained in the first step is heated and / or washed. The present invention relates to a method for producing a lithium-silicate stabilized niobic acid sol containing lithium and silicic acid as a dispersion stabilizer, the method comprising the steps of: [4] (1) First step of mixing ammonium niobate sol with inorganic acid (2) A 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 with a silica sol and a lithium compound. (4) A fourth step in which the mixture obtained in the third step is heated and / or washed. The present invention relates to a method for producing a lithium-silicate stabilized niobic acid sol containing lithium and silicic acid as a dispersion stabilizer, the method comprising the steps of: DETAILED DESCRIPTION OF THE INVENTION

[0010] 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 expression "numeric value 1 to numerical value 2" in relation to a numerical range means a numerical range including both the numerical values ​​1 and 2, with numerical value 1 being the lower limit and numerical value 2 being the upper limit, and is synonymous with "numerical value 1 or more and numerical value 2 or less."

[0011] The present invention relates to a lithium-silicic acid stabilized niobic acid 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 said to be a niobic acid sol stabilized with lithium and silicic acid.

[0012] In the sol of the present invention, at least a portion of the lithium is thought to directly bond to or adsorb onto dispersed particles of niobic acid, thereby contributing to the dispersion stabilization of the dispersed particles, similar to the lithium-stable niobic acid sol described in Patent Document 3. On the other hand, the remaining lithium is thought to indirectly contribute to the dispersion stabilization of the dispersed particles together with the coexisting silicic acid.

[0013] The Li / Nb (molar ratio) in the sol of the present invention is preferably in the range of 0.25 to 2.0 (Li / Nb2O5 (molar ratio) is in the range of 0.5 to 4.0). The lower limit of the Li / Nb (molar ratio) is more preferably 0.3. The upper limit of the Li / Nb (molar ratio) is more preferably 1.5.

[0014] The presence of silicic acid further stabilizes the sol of the present invention, which is believed to be due to the fact that silicic acid inhibits the precipitation of lithium niobate. Examples of silicic acid include water-soluble silicic acid such as metasilicic acid and orthosilicic acid, and colloidal silica that constitutes silica sol. Note that silica sol is preferably a silica sol in an aqueous solvent, i.e., a so-called aqueous silica sol.

[0015] The content of silicic acid in the sol of the present invention is not particularly limited as long as it is an amount that can stabilize the sol. A suitable range of the silicic acid content is preferably a range of 0.1 to 4.0 in terms of Si / Nb (molar ratio). The lower limit of this range is more preferably 0.5. The upper limit of this range is more preferably 3.0, and even more preferably 2.5.

[0016] The sol of the present invention is permissible to contain ammonia. The content of ammonia in the sol of the present invention is not particularly limited, but is preferably in the range of 0 or more and less than 0.5 as NH3 / Nb (molar ratio). The upper limit of the above range is more preferably less than 0.3, and even more preferably less than 0.2. When ammonia is contained, the lower limit of the above range is preferably, for example, 0.005 or more, but from the viewpoint of even lower content, it is preferably 0.001 or more. When ammonia is contained, the ammonia in the dispersed particles is thought to be bound to or adsorbed to the dispersed particles at the same location as lithium in the dispersed particles.

[0017] The pH of the sol of the present invention is preferably in the range from neutral to alkaline, for example, in the range of pH value 7 to 13. It is more preferably alkaline, for example, in the range of pH value 8 to 13.

[0018] (Manufacturing method) The sol of the present invention is preferably produced by the following first or second production method. The suitable composition ratios and the like can be those explained above unless otherwise specified. Furthermore, there are no particular limitations on the mixing method used in the mixing process, and mixing can be carried out by a conventional method.

[0019] (First manufacturing method) The first production method includes the following first and second steps. (1) First step of mixing ammonium niobate sol and lithium silicate (2) A second step in which the mixture obtained in the first step is heated and / or washed.

[0020] The ammonium niobate sol used as a raw material will now be described. Ammonium niobate sol and its manufacturing method are described in detail in Patent Document 1, so only a brief summary will be provided here. Ammonium niobate sol is a water-dispersed sol in which amorphous ammonium niobate microparticles are dispersed as colloidal particles. When the sol is dried at 100°C for 10 hours, the ammonia to niobic acid ratio (NH3 / Nb) is in the range of 0.25 to 0.75 (NH3 / Nb2O5 (molar ratio) is 0.5 to 1.5). The ammonium niobate sol is manufactured by mixing and reacting an aqueous solution of a niobium compound dissolved in hydrofluoric acid or a mixed acid of hydrofluoric acid and sulfuric acid with an aqueous ammonia solution while maintaining a pH of 8 or higher to obtain a dispersion containing ammonium niobate microparticles, which is then filtered and washed. Commercially available ammonium niobate sols include, for example, "Bailar Nb-G6000" manufactured by Taki Chemical Industry Co., Ltd.

[0021] In the first step, ammonium niobate sol and lithium silicate are mixed. As the lithium silicate, a commercially available product may be used, such as "Lithium Silicate 35," "Lithium Silicate 45," and "Lithium Silicate 75" manufactured by Nippon Chemical Industry Co., Ltd., or lithium silicate solution manufactured by Honjo Chemical Co., Ltd.

[0022] In the second step, the mixture obtained in the first step is heated and / or washed. This treatment is preferably carried out for the purpose of removing ammonia. For example, in the sol of the present invention, this treatment is carried out until the NH3 / Nb (molar ratio) becomes less than 0.5.

[0023] The heating conditions of temperature and time in the heat treatment may 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 may be set as appropriate depending on the heating temperature, but is, for example, 0.5 to 8 hours. By optimizing the amount of lithium present and the heating conditions, it is possible 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 considered to be 0. The Kjeldahl method is used to measure ammonia.

[0024] The washing method is not particularly limited, but is preferably ultrafiltration while adding water. 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 alone or in combination. When using both, for example, washing may be performed after heating, or heating may be performed after washing.

[0025] The mechanism of ammonia removal by heating and / or washing treatment is presumed to be as follows: In the ammonium niobate sol, there are almost no ammonium ions, and it is presumed that ammonia exists in a state bound to or adsorbed on fine particles of niobic acid. At least a portion of the ammonia is substituted with lithium, thereby generating free ammonia, which is volatilized by heating and discharged outside the system by washing.

[0026] After the second step, a filtration step and a concentration adjustment step may be carried out as necessary.

[0027] (Second manufacturing method) The second production method includes the following steps 1 to 4. (1) First step of mixing ammonium niobate sol with inorganic acid (2) A 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 with a silica sol and a lithium compound. (4) A fourth step in which the mixture obtained in the third step is heated and / or washed.

[0028] 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 determined depending on the target amount of ammonia removal in the second step, but as a guideline, the inorganic acid / Nb2O5 (molar ratio) ranges from 0.5 to 2. As the amount of inorganic acid added increases, the solution tends to become gel-like. Examples of inorganic acids include hydrochloric acid, nitric acid, and sulfuric acid, and of these, hydrochloric acid is particularly preferred. There are no particular limitations on the method for mixing the ammonium niobate sol and the inorganic acid; the inorganic acid may be added to the ammonium niobate sol, or vice versa.

[0029] The washing method in the second step is not particularly limited as long as it can remove ammonia, but ultrafiltration while adding water is preferred. By optimizing the washing method and conditions, it is possible to reduce the ammonia content in the sol of the present invention to below the detection limit, but it is preferable to wash until the NH3 / Nb2O5 (molar ratio) is at least less than 0.5. Washing can desalt the sol and also induce gelation, so a desalted gel can be obtained by washing in the second step.

[0030] In the third step, the demineralized gel, silica sol, and lithium compound are mixed together. The silica sol and lithium compound may be in any of the following forms: (i) a mixture of the silica sol and the lithium compound, (ii) a mixture of the silica sol and the lithium compound, or (iii) a lithium silicate mixture.

[0031] Here, the raw materials used for the (i) form and the (ii) form will be explained. The silica sol is preferably an aqueous silica sol. Examples of commercially available silica sols include the Snowtex series manufactured by Nissan Chemical Industries, Ltd., the Cataloid series manufactured by JGC Catalysts and Chemicals Co., Ltd., and the Silicadol series manufactured by Nippon Chemical Industry Co., Ltd. Examples of the lithium compound include lithium hydroxide, lithium carbonate, lithium hydrogen carbonate, etc., and preferably lithium hydroxide. The lithium compound is preferably in the form of an aqueous solution.

[0032] In the 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 the form (ii), a mixture of silica sol and a lithium compound may be used, or the mixture may be heated to dissolve the colloidal silica. In the form (iii), the same type of lithium silicate as in the first step of the first production method can be used.

[0033] In one embodiment of the third step, the demineralized gel and the silica sol are mixed and heated, and then a lithium compound is added. This embodiment is also included in the category of the third step. The heating in this embodiment may be carried out in the same manner as in the second step of the first production method.

[0034] 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 production method.

[0035] After the fourth step, a filtration step and a concentration adjustment step may be carried out as necessary.

[0036] The Nb concentration of the sol of the present invention is preferably, for example, in the range of 0.5 to 30 mass%. From the economical viewpoint of production and transportation, the lower limit is more preferably 2 mass%, even more preferably 3 mass%, and even more preferably 4 mass%. The upper limit of 30 mass% is set from the viewpoint of avoiding a decrease in handleability due to high viscosity. In consideration of convenience in production and use, the upper limit is more preferably 20 mass%, even more preferably 15 mass%.

[0037] The concentration of the sol of the present invention may be adjusted by a conventional method within a range in which the sol remains stable, such as by concentrating by heating or vacuum, or by diluting with water.

[0038] The sol of the present invention has excellent handleability and can be suitably used in various applications. Examples include a coating solution for forming a transparent thin film containing the sol of the present invention, and additives for secondary batteries, electronic materials, etc. When preparing a coating solution for forming a transparent thin film, the sol of the present invention can also be mixed with a hydrophilic solvent. Various additives, such as polymer compounds such as resin emulsions, silica compounds such as silica sols and silane coupling agents, surfactants, and oxide sols with photocatalytic activity, may be added to the coating solution as needed. [Example]

[0039] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0040] (Ammonium niobate sol) As the ammonium niobate sol, "Baylal Nb-G6000" (Nb=4.3 mass %, pH 8.8, NH3 / Nb (molar ratio)=0.6) manufactured by Taki Chemical Co., Ltd. was used.

[0041] Examples 1 to 3 To 300 g of stirred ammonium niobate sol, "Lithium Silicate 35" (SiO2 = 21.1 mass%, Li2O = 2.9 mass%, Si / Li (molar ratio) = 1.8) or "Lithium Silicate 45" (SiO2 = 21.2 mass%, Li2O = 2.4 mass%, Si / Li (molar ratio) = 2.2) manufactured by Nippon Chemical Industry Co., Ltd. was added (the type of lithium silicate and the amount of each raw material added were designed to achieve the composition shown in Table 1). The resulting solution was then 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 niobium sol stabilized with lithium and silicic acid, containing 4.3 mass% niobium as Nb. As in the following examples, heating was carried out in the open, and water was added as needed to adjust the concentration to a predetermined level.

[0042] [Table 1]

[0043] Table 2 shows the physical properties of the obtained sol. The sol was subjected to analysis in its original form, including the following analysis. Haze and total light transmittance: Measured using a haze meter "COH7700" manufactured by Nippon Denshoku Industries Co., Ltd., at wavelengths of 400 to 700 nm (10 nm intervals) with an optical path length of 10 mm.

[0044] [Table 2]

[0045] Example 4 1000 g of ammonium niobate sol was diluted with ion-exchanged water to 1.0% NbO by mass, and then 5% hydrochloric acid was added to achieve a HCl / NbO molar ratio of 1.5. The resulting solution was then filtered and washed using an ultrafiltration device to obtain a desalted gel. Next, Nissan Chemical Industries, Ltd.'s Snowtex ST-C (hereinafter referred to as "ST-C") silica sol was added to the desalted gel to achieve a Si / Nb molar ratio of 1.0. A 5% by mass aqueous solution of lithium hydroxide was then added to achieve a Li / Nb molar ratio of 1.0, and the mixture was heated at 90°C for 3 hours. Finally, the mixture was filtered to remove impurities, and the concentration was adjusted by adding an appropriate amount of water, if necessary, to obtain a niobium sol stabilized with lithium and silicic acid, containing 4.3% by mass of niobium as Nb.

[0046] Example 5 A niobic acid sol stabilized with lithium and silicic acid containing 4.3 mass% of niobium as Nb was obtained in the same manner as in Example 4, except that Cataloid SN (hereinafter referred to as "SN") manufactured by JGC Catalysts and Chemicals Co., Ltd. was added as the silica sol instead of ST-C so that the Si / Nb (molar ratio) was 1.0.

[0047] Example 6 To the desalted gel obtained in the same manner as in Example 4, ST-C was added as silica sol so that the Si / Nb (molar ratio) was 1.0, and the mixture was heated at 90°C for 3 hours. Next, a 5 mass% lithium hydroxide aqueous solution was added so that the Li / Nb (molar ratio) was 1.0, and the mixture was 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 niobic acid sol stabilized with lithium and silicic acid, containing 4.3 mass% niobium as Nb.

[0048] Example 7 A niobic acid sol stabilized with lithium and silicic acid containing 4.3 mass% of niobium as Nb was obtained in the same manner as in Example 6, except that SN was added as the silica sol instead of ST-C so that the Si / Nb (molar ratio) was 1.0.

[0049] Example 8 ST-C was used as silica sol, and a 5% by mass aqueous solution of lithium hydroxide was added to it so that the Si / Li (molar ratio) was 1.0. The mixture was heated at 50°C for 5 hours and then left overnight at room temperature to obtain a colorless and transparent aqueous solution of lithium silicate A with a pH of 12.6. To the desalted gel obtained in the same manner as in Example 4, lithium silicate aqueous solution A was added so that the Si / Nb (molar ratio) and Li / Nb (molar ratio) were 1.0 and 1.0, respectively, and the mixture was heated at 90° C. for 3 hours. Finally, the mixture was filtered to remove impurities, and then, if necessary, the concentration was adjusted by adding an appropriate amount of water to obtain a niobic acid sol stabilized with lithium and silicic acid, containing 4.3 mass % of niobium as Nb.

[0050] Example 9 SN was used as silica sol, and a 5% by mass aqueous solution of lithium hydroxide was added to it so that the Si / Li (molar ratio) was 1.0. The mixture was heated at 50°C for 5 hours and then left overnight at room temperature to obtain a colorless and transparent aqueous solution of lithium silicate B with a pH of 11.3. A niobic acid sol stabilized with lithium and silicic acid, containing 4.3 mass % of niobium as Nb, was obtained in the same manner as in Example 8, except that the lithium silicate aqueous solution B was added instead of the lithium silicate aqueous solution A so that the Si / Nb (molar ratio) and Li / Nb (molar ratio) were 1.0 and 1.0, respectively.

[0051] The physical properties of the sols obtained in Examples 4 to 9 were measured in the same manner as above, and the results are shown in Table 3.

[0052] [Table 3]

[0053] All of the sols obtained in Examples 1 to 9 were stored at 25° C. for one month, and no precipitate was observed, confirming that they had storage stability.

Claims

1. A lithium-silicic acid stabilized niobic acid sol containing lithium and silicic acid as dispersion stabilizers.

2. 2. The lithium-silicate stabilized niobic acid sol according to claim 1, 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 second step in which the mixture obtained in the first step is heated and / or washed. The present invention relates to a method for producing a lithium-silicic acid stabilized niobic acid sol containing lithium and silicic acid as a dispersion stabilizer, the method comprising the steps of:

4. (1) First step of mixing ammonium niobate sol with inorganic acid (2) A 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 with a silica sol and a lithium compound. (4) A fourth step in which the mixture obtained in the third step is heated and / or washed. The present invention relates to a method for producing a lithium-silicic acid stabilized niobic acid sol containing lithium and silicic acid as a dispersion stabilizer, the method comprising the steps of:

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