Lithium-inorganic acid stabilized niobate sol

Abstract

To develop niobic acid sol having fine particles of larger particle size stably dispersed.SOLUTION: A lithium-inorganic acid stable niobic acid sol contains, as a dispersion stabilizer, lithium and inorganic acid. The inorganic acid is preferably at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid and perchloric acid. A suitable production method for the sol includes a first step for mixing niobic acid ammonium sol with inorganic acid, a second step for mixing a liquid resulting from the first step with lithium hydroxide, and a third step for heating and / or cleaning a liquid resulting from the second step.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a lithium-inorganic acid-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] The lithium-stable niobic acid sol obtained by the manufacturing method disclosed in Patent Document 3 was a sol in which relatively small particles with an average particle size of about 10 to 30 nm were dispersed. Controlling particle size has been required from the viewpoint of expanding application areas.

[0006] An object of the present invention is to develop a niobic acid sol in which fine particles with a larger particle size are stably dispersed, particularly a niobic acid sol with an average particle size of 50 nm or more. [Means for solving the problem]

[0007] 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 an inorganic acid as a dispersion stabilizer, and have completed the present invention based on this finding.

[0008] That is, the present invention is as follows. [1] A lithium-inorganic acid stabilized niobic acid sol containing lithium and an inorganic acid as a dispersion stabilizer. [2] The lithium-inorganic acid-stable niobic acid sol according to the above [1], wherein the inorganic acid is at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, and perchloric acid. [3] (1) First step of mixing ammonium niobate sol with inorganic acid (2) A second step of mixing the mixture obtained in the first step with lithium hydroxide. (3) A third step in which the liquid obtained in the second step is heated and / or washed. The present invention relates to a method for producing a lithium-inorganic acid-stabilized niobic acid sol containing lithium and an inorganic acid as a dispersion stabilizer, the method comprising the steps of: DETAILED DESCRIPTION OF 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 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."

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

[0011] 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 inorganic acid.

[0012] The Li / Nb (molar ratio) in the sol of the present invention is preferably in the range of 0.25 to 1.5 (Li / Nb2O5 (molar ratio) is in the range of 0.5 to 3.0). In this range, it is believed that the majority of lithium is bound to or adsorbed on the dispersed particles of niobic acid, thereby achieving dispersion stabilization. The lower limit of the Li / Nb (molar ratio) is more preferably 0.3 or more. The upper limit of the Li / Nb (molar ratio) is more preferably 1.25 or less, and even more preferably 1.0.

[0013] The presence of an inorganic acid allows for an increase in particle size. Furthermore, the sol is stabilized, presumably because the inorganic acid inhibits the precipitation of lithium niobate. The type of inorganic acid is preferably at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, and perchloric acid.

[0014] The content of the inorganic acid in the sol of the present invention is not particularly limited, but is preferably an amount that ensures at least stability of the sol. The preferred range of the content of the inorganic acid varies depending on the type of inorganic acid, and for example, it is preferred that the nitric acid / Li (molar ratio) is in the range of 0.40 to 0.50 for nitric acid, the hydrochloric acid / Li (molar ratio) is in the range of 0.30 to 0.50 for hydrochloric acid, the sulfuric acid / Li (molar ratio) is in the range of 0.15 to 0.25 for sulfuric acid, and the perchloric acid / Li (molar ratio) is in the range of 0.45 to 0.55 for perchloric acid.

[0015] 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 0.25 as NH3 / Nb (molar ratio). The upper limit of the above range is more preferably less than 0.2, and even more preferably less than 0.1. 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.

[0016] A preferred embodiment of the sol of the present invention has an average particle size of 50 nm or more. The upper limit of the average particle size is not particularly limited as long as the properties of the sol are maintained without causing precipitation, but a preferred example is 300 nm. Therefore, a preferred range is 50 to 300 nm. The upper limit is more preferably 250 nm, and even more preferably 200 nm.

[0017] (Manufacturing method) A suitable method for producing the sol of the present invention comprises the following first to third steps. (1) First step of mixing ammonium niobate sol with inorganic acid (2) A second step of mixing the mixture obtained in the first step with lithium hydroxide. (3) A third step in which the liquid obtained in the second step is heated and / or washed.

[0018] 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.

[0019] In the first step, ammonium niobate sol and an inorganic acid are mixed. There are no particular limitations on the method for mixing the two, and they may be mixed by a conventional method. For example, the inorganic acid is added to the ammonium niobate sol under stirring. The mixture obtained by this mixing is usually a semi-solid with very high viscosity. The type of inorganic acid is preferably at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, and perchloric acid.

[0020] In the second step, the mixture obtained in the first step is mixed with lithium hydroxide. Usually, the viscosity of the mixture decreases by mixing with lithium hydroxide, and the mixture becomes liquid. There are no particular limitations on the method for mixing the two, and they can be mixed by a conventional method. For example, lithium hydroxide is added to the mixture obtained in the first step while stirring.

[0021] In the third step, the liquid obtained in the second 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 0.25.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] After the third step, a filtration step and a concentration adjustment step may be carried out as necessary.

[0026] 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%.

[0027] 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.

[0028] The sol of the present invention has high handleability and can be suitably used in various applications, such as a coating solution for forming a transparent thin film containing the sol of the present invention, an additive for secondary batteries, electronic materials, etc. [Example]

[0029] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0030] Examples 1 to 4 As the ammonium niobate sol, "Baylal Nb-G6000" manufactured by Taki Chemical Industry Co., Ltd. (Nb=4.3 mass %, pH 8.8, NH3 / Nb (molar ratio)=0.6, average particle size: 15 nm) was used. To 300 g of ammonium niobate sol under stirring, an inorganic acid was added, followed by lithium hydroxide (the type of inorganic acid and the amount of each raw material added were designed to achieve the composition shown in Table 1). Next, the resulting solution was heated at 90°C for 3 hours. Heating was performed in the open air, and water was added as needed to adjust the concentration to a predetermined level. Finally, the solution 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 an inorganic acid, having the Nb concentration shown in Table 1.

[0031] [Table 1]

[0032] Table 2 shows the physical properties of the obtained sol. The sol was subjected to analysis in its original form, including the following analysis. Average particle size: Measured using a dynamic light scattering particle size distribution analyzer "LB-500" manufactured by Horiba Ltd. 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.

[0033] [Table 2]

[0034] All of the sols obtained in Examples 1 to 4 had an average particle size of 50 nm or more, and furthermore, when stored at 25°C for one month, no precipitate was observed, confirming that they had storage stability.

Claims

1. A lithium-inorganic acid stabilized niobic acid sol containing lithium and an inorganic acid as a dispersion stabilizer and having an average particle size of 50 to 300 nm.

2. 2. The lithium-inorganic acid-stable niobic acid sol according to claim 1, wherein the inorganic acid is at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, and perchloric acid.

3. (1) First step of mixing ammonium niobate sol with inorganic acid (2) A second step of mixing the mixture obtained in the first step with lithium hydroxide. (3) A third step in which the liquid obtained in the second step is heated and / or washed. The method for producing a lithium-inorganic acid stabilized niobic acid sol contains lithium and an inorganic acid as a dispersion stabilizer and has an average particle size of 50 to 300 nm, comprising:

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