Method for producing titanic acid compound and titanic acid compound

Abstract

The present invention provides a method for producing a titanic acid compound, with which a titanic acid compound having high charging and discharging capacity can be produced. The present invention relates to a method for producing a titanic acid compound represented by general formula HxTiyＯz (x>0, y>0, z>0). The method includes: a preparation step for preparing at least one type of alkali metal titanium oxide selected from the group consisting of cubic-Li2TiＯ3, α-Na2TiO3, β-Na2TiO3 and Na8Ti5O14 as a starting material by using a solid phase method; an acid treatment step for subjecting the alkali metal titanium oxide to an acid treatment; and a heat treatment step for heat treating a compound subjected to the acid treatment.

Description

Titanic acid compound manufacturing method and titanic acid compound

[0001] The present invention relates to a method for producing a titanic acid compound and to a titanic acid compound.

[0002] Lithium secondary batteries have a higher energy density than other power storage devices and are therefore widely used as batteries for mobile terminals, wearable devices, drones, etc. In recent years, they have also been applied to large-scale power storage devices that require large capacity, such as those for vehicles. Therefore, the active materials used in such lithium secondary batteries are required to have high charge / discharge capacities.

[0003] For example, in Patent Document 1, a compound of the composition formula H exhibiting an XRD pattern corresponding to bronze-type titanium dioxide is disclosed. ｘ Ti ｙ O ｚ (0.02<x / y<0.40, 2.01<z / y<2.30) is disclosed. Patent Document 1 describes that when such titanium oxide is used, the battery capacity of a lithium secondary battery is improved and the cycle characteristics are excellent.

[0004] In addition, in Patent Document 2, the general formula H ２ Ti １２ O ２５ and discloses a titanium oxide in which the amount of alkali metals other than lithium detected by ICP emission spectroscopy is less than the lower limit of quantification. Patent Document 2 describes that the use of such a titanium oxide improves the charge / discharge capacity of an electricity storage device. Furthermore, Non-Patent Documents 1 to 3 describe the preparation of cubic-Li by a method such as a hydrothermal method. ２ TiO ３ and Na ２ TiO ３ and the like.

[0005] International Publication No. 2009 / 028530 Japanese Patent Application Laid-Open No. 2020-117416

[0006] A. Laumann, KT Fehr, M. Wachsmann, M. Holzapfel, BB Iversen, Solid State Ionics, Vol.181(2010), 1525-1529.T. Xue, L. Wang, T. Qi, J. Chu, J. Qu, C. Liu, Hydrometallurgy, Vol.95(2009), 22-27.F. Meng, Y. Liu, T. Xue, Q. Su, W. Wang, T. Qi, RSC Advances, Vol.6(2016), 112625.

[0007] Several novel titanate compounds with high charge-discharge capacities have been reported, but in order to obtain high charge-discharge capacities, it is necessary to synthesize precursor particles using a hydrothermal method or a solvothermal method, which is not economical. On the other hand, when preparing titanate compounds using a cost-saving method such as a solid-phase method, Na ２ Ti ３ O ７ or Na ２ Ti ６ O １３ However, it has been difficult to synthesize compounds that exhibit high charge / discharge capacities.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a titanate compound that exhibits a high charge / discharge capacity and a method for producing the same.

[0009] As a result of extensive investigation, the present inventors have found that cubic-Li was synthesized as a starting material by a solid phase method. ２ TiO ３ , α-Na ２ TiO ３ , β-Na ２ TiO ３ , and Na ８ Ti ５ O １４a preparation step of preparing at least one alkali metal titanium oxide selected from the group consisting of: ｘ Ti ｙ O ｚ The present inventors have found that it is possible to prepare a titanic acid compound represented by (x>0, y>0, z>0), and have completed the present invention.

[0010] That is, the method for producing a titanic acid compound of the present embodiment is a method for producing a titanic acid compound by reacting a compound of the general formula H ｘ Ti ｙ O ｚ (x>0, y>0, z>0), a starting material is a cubic-Li compound obtained by a solid phase method. ２ TiO ３ , α-Na ２ TiO ３ , β-Na ２ TiO ３ , and Na ８ Ti ５ O １４ The method includes a preparation step of preparing at least one alkali metal titanium oxide selected from the group consisting of: an acid treatment step of acid-treating the alkali metal titanium oxide; and a heat treatment step of heat-treating the acid-treated compound.

[0011] According to the present invention, a method for producing a titanate compound exhibiting high charge / discharge capacity can be provided, and by using the titanate compound as an active material for an electrode, a lithium secondary battery exhibiting excellent charge / discharge capacity can be provided.

[0012] FIG. 1 shows an XRD pattern after each step in Example 1. FIG. 2 shows an XRD pattern after each step in Example 2. FIG. 3 shows an XRD pattern after each step in Example 3. FIG. 4 shows an XRD pattern after each step in Example 4. FIG. 5 shows an XRD pattern after each step in Example 5. FIG. 6 shows an XRD pattern of a titanate compound in Comparative Example 1. FIG. 7 shows an XRD pattern of a titanate compound in Comparative Example 2. FIG. 8 shows an XRD pattern after each step in Example 6. FIG. 9 shows an XRD pattern after a heat treatment step in Example 7. FIG. 10 shows an XRD pattern after a heat treatment step in Example 9. FIG. 11 shows an XRD pattern after a heat treatment step in Example 10. FIG. 12 shows an XRD pattern after each step in Comparative Example 3.

[0013] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail, but the present invention is not limited to the following embodiment. The present invention can be modified in various ways without departing from the gist of the present invention.

[0014] Recently, titanium hydride oxide (H2O3) has been developed as a titanate compound that exhibits high charge-discharge capacity as an active material for electrodes. ２ Ti １２ O ２５ etc.) and titanium niobium oxide (TiNb ２ O ７ (e.g., etc.) have been reported. However, in order to obtain a high charge / discharge capacity, it is necessary to synthesize a precursor of fine particles using a hydrothermal method, a solvothermal method, etc., but using the above methods is economically disadvantageous because it requires many processes and expensive raw materials. On the other hand, when titanate compounds are prepared using a cost-effective method such as the solid-phase method, it tends to be difficult to synthesize compounds that exhibit high charge / discharge capacities.

[0015] Therefore, the present inventors have developed a method for producing cubic-Li by a solid phase method. ２ TiO ３ , α-Na ２ TiO ３ , β-Na２ TiO ３ , and Na ８ Ti ５ O １４ It has been found that a titanate compound exhibiting a high charge / discharge capacity as an active material for an electrode can be produced by using a method for producing a titanate compound, the method comprising the steps of: preparing at least one alkali metal titanium oxide selected from the group consisting of:

[0016] The reason why the titanate compound obtained by such a manufacturing method exhibits a high charge-discharge capacity is not entirely clear. However, it is believed that the cubic-Li, which is a precursor material of the titanate compound, is used in the manufacturing process. ２ TiO ３ , α-Na ２ TiO ３ , β-Na ２ TiO ３ , and Na ８ Ti ５ O １４ It is presumed that this is because the actual capacity utilization rate of the original titanate compound was improved by being able to form the fine particles of the above-mentioned compound by a solid phase method. However, the reason is not limited to this. 1. Method for Producing Titanate Compound The method for producing a titanate compound of this embodiment (hereinafter also referred to as "the present production method") is a method for producing a titanate compound of the general formula H ｘ Ti ｙ O ｚ (x>0, y>0, z>0) (hereinafter also simply referred to as "titanic acid compound"), a starting material is a cubic-Li ２ TiO ３ , α-Na ２ TiO ３ , β-Na ２ TiO ３ , and Na ８ Ti ５ O １４The method includes the steps of: preparing at least one alkali metal titanium oxide selected from the group consisting of: an acid treatment step of acid-treating the alkali metal titanium oxide; and a heat treatment step of heat-treating the acid-treated compound. According to the method, a titanate compound exhibiting high charge / discharge capacity can be produced at low cost.

[0017] 1.1. Preparation of Alkali Metal Titanium Oxide The method for producing a titanic acid compound is to prepare cubic-Li as a starting material by a solid phase method. ２ TiO ３ , α-Na ２ TiO ３ , β-Na ２ TiO ３ , and Na ８ Ti ５ O １４ The method includes a preparation step of preparing at least one alkali metal titanium oxide selected from the group consisting of: Since the raw materials are prepared by a solid-phase method, the target substance can be produced at low cost. The solid-phase method refers to a production method in which multiple solid-phase compounds serving as starting materials are mixed and then heated to synthesize the target substance.

[0018] The preparation process involves powdered TiO ２ and an alkali metal hydroxide (including its hydrate) by a known method, followed by heating. Methods for mixing the powders include a dry or wet method in which the powders are placed in a mortar, mixer, mill, etc. (a drying step is included in the case of the wet method), and a method in which the powder is dissolved or suspended in a liquid such as water or an organic solvent and then dried (including a crushing step after drying). Preferably, the method involves dissolving and suspending the powder in water and then drying (including a crushing step after drying).

[0019] The alkali metal hydroxide is not particularly limited, but is preferably lithium hydroxide monohydrate (LiOH·H ２ The use of these alkali metal hydroxides tends to more reliably obtain the titanic acid compound of the present invention, and the effects of the present invention can be more effectively and reliably achieved. ２When the titanium dioxide powder is mixed with the alkali metal hydroxide, the reaction to obtain the titanate compound does not occur. ２ and the molar ratio of alkali metal hydroxide (TiO ２ The molar ratio of the hydroxide (water: alkali metal hydroxide) is not particularly limited, but is preferably 1:4 to 1:1, 1:3 to 4:5, or 1:2 to 5:8. By setting the molar ratio in this range, the effects of the present invention tend to be more effectively and reliably exhibited.

[0020] TiO used in the preparation process ２ The crystal structure of TiO is not particularly limited, and may be a rutile type, an anatase type, or a brookite type. The rutile type and the anatase type are preferred. ２ The temperature to which the mixture is heated is not particularly limited, but is preferably 300°C or higher and 1000°C or lower, 350°C or higher and 900°C or lower, 400°C or higher and 800°C or lower, 400°C or higher but lower than 800°C, or 450°C or higher and 750°C or lower. ２ The time for heating the mixture is not particularly limited, but is preferably 30 minutes to 20 hours, 50 minutes to 15 hours, or 80 minutes to 12 hours. By setting the heating temperature and time in the preparation step within the above ranges, the effects of the present invention tend to be more effectively and reliably achieved.

[0021] TiO used as a raw material in the preparation process ２ The particle size of TiO is not particularly limited, but is preferably 1 nm or more and 400 nm or less, 2 nm or more and 300 nm or less, 3 nm or more and 250 nm or less, or 5 nm or more and 200 nm or less. ２ By setting the particle size within the above range, the resulting titanate compound tends to further improve the charge-discharge characteristics as an electrode active material.

[0022] In this embodiment, the particle size is measured by a microscopic method. ２The particle size of a sample such as the above can be measured, for example, as follows: A photograph of the sample is taken with a transmission electron microscope or a scanning electron microscope at a magnification (10,000 to 500,000 times) that allows the particle shape to be sufficiently confirmed, and the particle shape (i.e., the projected image of the particle) is approximated on the photograph to a sphere inscribed with the particle. 100 or more primary particles are randomly selected from the photograph, and the diameter of the approximated sphere is measured. The obtained measurement value is converted using the dimensions of the scale bar on the photograph to determine the primary particle size of each particle, and the weight average of these primary particle diameters is taken as the particle size.

[0023] The alkali metal titanium oxide, which is the precursor of the titanic acid compound obtained in the preparation step, is cubic-Li ２ TiO ３ , α-Na ２ TiO ３ , β-Na ２ TiO ３ , and Na ８ Ti ５ O １４ At least one alkali metal titanium oxide selected from the group consisting of: ２ TiO ３ , α-Na ２ TiO ３ , and Na ８ Ti ５ O １４ The alkali metal titanium oxide is at least one selected from the group consisting of: By using the alkali metal titanium oxide obtained by the preparation step of this embodiment, the resulting titanate compound tends to contribute more to the charge-discharge characteristics.

[0024] In the preparation step, the alkali metal titanate compound obtained is cubic-Li ２ TiO ３ When the hydrogen ion concentration is less than 0.1 mol / L, the hydrogen ion concentration is less than 0.1 mol / L. ２ SO ４ , HNO ３ It is preferable to suspend the cubic-Li in an inorganic acid such as acetic acid, citric acid, or an organic acid such as acetic acid, citric acid, or oxalic acid, then filter and dry the cubic-Li, and then heat the cubic-Li in the air before proceeding to the next step.２ TiO ３ Some of the lithium ions inside are dissolved and heated to form cubic-Li ２ TiO ３ In the dehydration process in the heat treatment step after the acid treatment step, a different crystal structure can be compounded in the crystal structure of TiO such as anatase type or rutile type. ２ As specific conditions, the conditions described in the examples below may be used.

[0025] In the solid phase method, it is preferable that the heating temperature is 400° C. or higher and lower than 800° C., and the heating time is 1 hour or longer. By setting the heating temperature and heating time within the above ranges, it is possible to obtain γ-Na ２ TiO ３ From the same viewpoint, it is more preferable that the heating temperature is 400° C. or higher and 780° C. or lower, and the heating time is 80 minutes or longer.

[0026] 1.2. Acid Treatment Step The method for producing a titanate compound includes a step of acid-treating the alkali metal titanate compound obtained in the preparation step. In the acid treatment step, the alkali metal titanate compound is suspended in an acid aqueous solution, followed by filtration and drying. The acid aqueous solution is not particularly limited, but may be HCl, H ２ SO ４ , HNO ３ An aqueous solution of any concentration containing one or more inorganic acids such as acetic acid, citric acid, oxalic acid, etc., or organic acids such as acetic acid, citric acid, oxalic acid, etc., can be used. The hydrogen ion concentration is preferably 0.1 mol / L to 6.0 mol / L based on the aqueous HCl solution and the aqueous citric acid solution. The acid treatment step can convert the alkali metal titanate compound into a precursor of the titanate compound of this embodiment. The acid treatment step may be additionally performed after the heat treatment step.

[0027] In the acid treatment step, the total time for suspending in the acid aqueous solution is preferably 1 to 72 hours. By keeping the total suspension time within the above range, the effects of the present production method tend to be more effective and reliable. From the same viewpoint, the total suspension time is more preferably 1 to 60 hours, even more preferably 1 to 48 hours, and even more preferably 1 to 24 hours.

[0028] After the acid treatment step, the obtained alkali metal titanium oxide sample preferably has peaks at 28.0° to 29.5° and 44.5° to 46.5° in the 2θ pattern of XRD. More preferably, the peaks are 28.0° to 29.3° and 44.7° to 46.3°, or 28.5° to 29.3° and 45.0° to 46.3°. When the diffraction peaks of the alkali metal titanium oxide are within the above ranges, the obtained titanate compound tends to contribute more to the charge-discharge characteristics.

[0029] 1.3. Heat Treatment Step The method for producing a titanate compound includes a heat treatment step of heat-treating the acid-treated compound. The heat treatment step involves heat-treating the titanate compound precursor obtained by the acid treatment step to obtain the titanate compound of the present embodiment described above. For example, heat treatment in an oxygen-containing atmosphere such as air, an inert gas atmosphere such as nitrogen or argon, a hydrogen gas atmosphere, or a vacuum can promote the desired dehydration reaction and produce titanium oxide. Among these, in order to more effectively and reliably achieve the effects of the heat treatment, heat treatment in an oxygen-containing atmosphere such as air, an inert gas atmosphere such as nitrogen or argon, or a vacuum is preferred, and air or a vacuum is even more preferred. In this specification, "vacuum" refers to a pressure atmosphere lower than atmospheric pressure, preferably a pressure maintained at 100 Pa or less.

[0030] The heating temperature in the heat treatment step is not particularly limited, but is preferably 200° C. or higher and 500° C. or lower, 240° C. or higher and 430° C. or lower, 250° C. or higher and 400° C. or lower, or 260° C. or higher and 350° C. or lower. Furthermore, the heating time in the heat treatment step is not particularly limited, but is preferably 0.5 hours or higher and 100 hours or lower, 1 hour or higher and 30 hours or lower, or 2 hours or higher and 10 hours or lower. By setting the heat treatment temperature and time in the heat treatment step within the above ranges, the effects of the present invention tend to be more effectively and reliably achieved.

[0031] 2. Titanic Acid Compound The titanic acid compound of this embodiment (hereinafter also simply referred to as "titanic acid compound") is a titanic acid compound obtained by the above-described production method, and is represented by the general formula H ｘ Ti ｙ O ｚ (x>0, y>0, z>0) The titanate compound obtained by this production method exhibits excellent charge / discharge capacity when used as an active material for electrodes of lithium secondary batteries.

[0032] In titanic acid compounds, the general formula is H ｘ Ti ｙ O ｚ (x>0, y>0, z>0). That is, the titanate compound is a titanium oxide containing at least H. Preferably, x, y, and z further satisfy the relational expressions of 0.15<x / y<0.37 and 2.0<z / y<2.19. The titanate compound obtained by this production method tends to satisfy such relational expressions. From the same viewpoint, it is more preferable that the titanate compound has a value close to x:y:z=2:12:25, and even more preferably x:y:z=2:12:25. Here, the value close to x:y:z=2:12:25 means that the titanate compound is originally a titanium oxide containing at least H. ｘ Ti ｙ O ｚ This refers to a case where a compound is presumed to have a structure represented by the formula: and it is difficult to derive the ratio due to errors caused by measurement limitations, etc.

[0033] The titanate compound of this embodiment preferably has peaks at 14.0° or more and 15.0° or less, 28.4° or more and 29.4° or less, and 44.7° or more and 45.7° or less in the 2θ pattern of XRD. Furthermore, the titanate compound more preferably has peaks at least at 14.0° or more and 14.9° or less, 28.4° or more and 29.4° or less, and 44.7° or more and 45.7° or less in an XRD 2θ pattern; has peaks at least at 14.0° or more and 15.0° or less, 28.5° or more and 29.3° or less, and 44.7° or more and 45.7° or less; has peaks at least at 14.0° or more and 15.0° or less, 28.5° or more and 29.3° or less, and 44.9° or more and 45.4° or less; has peaks at least at 14.0° or more and 15.0° or less, 28.6° or more and 29.2° or less, and 45.0° or more and 45.4° or less; and has peaks at least at 14.0° or more and 14.9° or less, 28.6° or more and 29.2° or less, and 45.0° or more and 45.4° or less. When the titanate compound has a peak within the above range in the 2θ pattern of XRD, it tends to more effectively and reliably improve the charge / discharge characteristics as an active material for an electrode.

[0034] In the titanate compound of this embodiment, in the 2θ pattern of XRD, the ratio (B / A) of the maximum peak intensity B at 48.0° to 49.0° to the maximum peak intensity A at 44.7° to 45.7° is preferably 0.5 or less. More preferably, the ratio (B / A) is 0.45 or less, 0.4 or less, or 0.3 or less. A small ratio (B / A) is one of the characteristics of the titanate compound of this embodiment, and therefore, the titanate compound tends to have excellent charge / discharge characteristics as an electrode active material.

[0035] In the titanate compound of this embodiment, the ratio (C / A) of the maximum peak intensity C at 52.4° to 53.4° inclusive to the maximum peak intensity A at 44.7° to 45.7° inclusive in an XRD 2θ pattern is preferably 0.2 or less. More preferably, the ratio (C / A) is 0.18 or less, 0.15 or less, or 0.10 or less. A small ratio (C / A) is one of the characteristics of the titanate compound of this embodiment, and therefore, the titanate compound tends to have excellent charge / discharge characteristics as an electrode active material.

[0036] In this embodiment, the method for measuring the X-ray diffraction pattern is not particularly limited, and the measurement may be performed by a conventionally known method. For example, the apparatus and measurement conditions used in the Examples described later can be used as one such method.

[0037] The hydrogen content in the titanate compound is H ２ The hydrogen content in the titanate compound is preferably 1.2% by mass or more and 4.0% by mass or less, more preferably 1.4% by mass or more and 3.8% by mass or less, even more preferably 1.6% by mass or more and 3.6% by mass or less, and particularly preferably 1.8% by mass or more and 3.5% by mass or less, in terms of the amount of O. When the hydrogen content in the titanate compound is within the above range, the charge / discharge characteristics as an active material for an electrode tend to be further improved. Note that the hydrogen content is the amount of H when the titanate compound is 100% by mass. ２ This is the O equivalent amount.

[0038] The method for measuring the hydrogen content in the titanate compound is not particularly limited, and may be measured by a conventional method. As an example, the hydrogen content can be measured using a thermogravimetric analyzer (TG-DTA). More specifically, the obtained titanate compound may be subjected to thermogravimetric measurement using a thermogravimetric analyzer (apparatus used: TG / DTA7200, manufactured by SII Nano Technology Co., Ltd.). For example, the water content may be a mass %, TiO ２ When the amount is (100-a) mass%, the coefficients of the titanium oxide composition formula can be calculated from the formula: x = 2(a / 18.015), y = (100-a) / 79.9, z = x / 2 + 2y (H ２ Molecular weight of O: 18.015, TiO ２(Molecular weight: 79.9) If the titanic acid compound has adsorbed water before the measurement, it is recommended to heat it at 150° C. to remove the adsorbed water before the measurement.

[0039] The particle diameter of the titanate compound is preferably 200 nm or less. With the particle diameter within the above range, the charge / discharge characteristics of a lithium secondary battery containing the titanate compound tend to be further improved. From the same viewpoint, the particle diameter of the titanate compound is more preferably 195 nm or less, even more preferably 150 nm or less, even more preferably 120 nm or less, and particularly preferably 100 nm or less. Furthermore, the particle diameter of the titanate compound may be 10 nm or more, 20 nm or more, or 30 nm or more.

[0040] 3. Lithium Secondary Battery Containing Titanate Compound An electrode containing a titanate compound obtained by the present production method is preferably used as a component of a lithium secondary battery, and can increase the charge / discharge capacity.

[0041] Lithium secondary batteries containing the titanate compound obtained by this production method have a high initial discharge capacity and excellent cycle characteristics. More specifically, the lithium secondary battery of this embodiment has an initial discharge capacity of 250 mAh / g or more, preferably 260 mAh / g or more, 265 mAh / g or more, 270 mAh / g or more, 280 mAh / g or more, 290 mAh / g or more, or 295 mAh / g or more. Furthermore, as for the cycle characteristics of the lithium secondary battery of this embodiment, the discharge capacity at the 10th cycle is preferably 250 mAh / g or more, 260 mAh / g or more, 265 mAh / g or more, 270 mAh / g or more, or 280 mAh / g or more. An example of a method for measuring the charge / discharge characteristics is described in the Examples below.

[0042] The titanate compound of the present embodiment is preferably used as an active material for a lithium secondary battery, and can increase the charge / discharge capacity of the lithium secondary battery. Among the components of the lithium secondary battery, the titanate compound is particularly preferably used as an active material for the negative electrode.

[0043] 3.2 Electrode Sheet The titanate compound of this embodiment is preferably used as an active material in an electrode sheet, and using such an electrode sheet in a lithium secondary battery can increase the charge / discharge capacity. The method for producing the electrode sheet of this embodiment is not particularly limited as long as it uses a titanate compound as the active material, but it may be produced, for example, by the method described in the Examples below.

[0044] 3.3 Other Components As components other than the titanate compound that constitute the lithium secondary battery, conventionally known components may be used as long as they do not interfere with the effects of the titanate compound of the present invention. Examples of such components include a positive electrode material, a conductive additive, a binder, and an electrolyte.

[0045] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0046] Example 1 TiO ２ (anatase, particle size: approximately 6 nm) and LiOH·H ２ O was dissolved and suspended in water at a molar ratio of 1:2, dried, and heated in air at 450°C for 80 minutes to obtain cubic-Li. ２ TiO ３ (Preparation step). ２ TiO ３ The resulting mixture was suspended in a 0.05M aqueous HCl solution for 1 hour, filtered, and dried. The mixture was then heated in air at 300°C for 5 hours, suspended in a 0.5M aqueous HCl solution for 24 hours, and then filtered and dried (acid treatment step). The XRD 2θ pattern of the sample thus obtained was measured, and diffraction peaks were confirmed at 28.7° and 44.7° (see FIG. 1b). Heat treatment was then performed in vacuum at 350°C for 5 hours to obtain the titanic acid compound of the present invention (heat treatment step). The XRD 2θ pattern of the obtained titanic acid compound was measured, and diffraction peaks were observed at almost the same positions as those of the titanium oxide (Comparative Example 2) disclosed in JP 2022-117416 A (see FIG. 1c). Therefore, H ２ Ti １２ O ２５It was confirmed that the compound was synthesized. In the XRD 2θ pattern, diffraction peaks were observed at 14.7 °, 28.8 °, and 45.2 °, and the ratio (B / A) of the maximum peak intensity B at 48.0 ° or more and 49.0 ° or less to the maximum peak intensity A at 44.7 ° or more and 45.7 ° or less was 0, and the ratio (C / A) of the maximum peak intensity C at 52.4 ° or more and 53.4 ° or less to the peak intensity A was confirmed to be 0. The titanium oxide obtained above was subjected to thermogravimetric analysis using a thermogravimetric analyzer (apparatus used: TG / DTA7200, manufactured by SII Nano Technology Co., Ltd.) in the same manner as in the method disclosed in JP 2020-117416 A, and the chemical composition was calculated. As a result, H in the obtained titanic acid compound ２ The hydrogen atom content of the O conversion was 3.1 mass%. ２ Ti １２ O ２５ H that will be included in ２ The content of hydrogen atoms in terms of O was about 1.9 mass %. This is because the titanic acid compound obtained in Example 1 could not completely remove the adsorbed water by heating at 150°C, and the remaining adsorbed water was included in the measured H ２ It is presumed that the error occurred due to the addition of hydrogen atoms to the content of O. It is also believed that similar measurement errors occurred in the samples described below.

[0047] For the 2θ patterns measured in the examples, curve fitting was performed by the least squares method using the 2θ patterns around the peaks as Gaussian functions to determine the positions of each peak. In particular, since there are peaks in which two or more peaks overlap in some areas, such curve fitting is effective. The formula for the Gaussian function is as follows:

[0048] (Fabrication of Lithium Secondary Battery and Evaluation of Charge and Discharge) The titanate compound obtained above was used as the active material, acetylene black as the conductive material, and polytetrafluoroethylene as the binder, and the mass ratio of active material:conductive material:binder was blended to 5:5:1 to fabricate an electrode, which was then treated and dried for 12 hours at 160°C in a vacuum of 10 Pa or less. A lithium secondary battery (coil-type cell) was fabricated, which included the electrode sheet thus fabricated, a counter electrode of lithium metal, and a 1M electrolyte solution prepared by dissolving lithium hexafluorophosphate in a mixed solvent (volume ratio 1:1) of ethylene carbonate (EC) and diethyl carbonate (DEC).

[0049] The electrochemical lithium insertion and extraction behavior (charge-discharge characteristics) of this lithium secondary battery was measured. Charge-discharge characteristics were tested at a temperature of 25°C, a current density of 10 mA / g, and a cutoff potential of 3.0 V to 1.0 V. The battery charge-discharge device used was an HJ-SD8 (product name, manufactured by Hokuto Denko Corporation). The initial discharge capacity was 295 mAh / g, and the discharge capacity at the 10th cycle was 286 mAh / g.

[0050] (X-ray Diffraction Measurement) The above-mentioned X-ray diffraction (XRD 2θ pattern) measurement was carried out using the following equipment and measurement conditions: Measurement equipment: RINT2550V (product name, manufactured by Rigaku Corporation) Measurement conditions: X-ray output (40 kV, 200 mA, Cu-Kα ray), measurement range (2θ = 5° to 89.99°, step width = 0.03°), scan speed (2° / min).

[0051] Example 2: TiO ２ Rutile (particle size: about 15 nm) and NaOH were dissolved and suspended in water in a molar ratio of 1:2, dried, and heated in air at 600°C for 12 hours to obtain α-Na ２ TiO ３ (Preparation step). ２ TiO ３ The resulting sample was suspended in a 0.5 M aqueous HCl solution for 24 hours, filtered, and then dried (acid treatment step). The 2θ pattern of the thus obtained sample was measured by XRD in the same manner as in Example 1, and diffraction peaks were confirmed at 28.0° and 46.0° (Fig. 2, 2b).

[0052] Next, heat treatment was carried out in a vacuum at 260° C. for 5 hours to obtain a titanic acid compound of the present invention (heat treatment step). The obtained titanic acid compound was measured for its 2θ pattern by XRD. As a result, it was found that the titanic acid compound had a 2θ pattern similar to that of Example 1. ２ Ti １２ O ２５ It was confirmed that the 2θ pattern of the XRD showed diffraction peaks at 14.3°, 28.8°, and 44.9° by the above-mentioned fitting, but no clear diffraction peaks were observed in the ranges of 48.0° to 49.0° and 52.4° to 53.4° (2c in FIG. 2). Therefore, in the 2θ pattern of the XRD, the ratio (B / A) of the maximum peak intensity B at 48.0° to 49.0° to the maximum peak intensity A at 44.7° to 45.7° was 0, and the ratio (C / A) of the maximum peak intensity C at 52.4° to 53.4° to the peak intensity A was also 0. Thermogravimetry of the titanate compound obtained above was performed in the same manner as in Example 1, and the chemical composition was calculated. As a result, it was confirmed that the H in the titanate compound ２ The content of hydrogen atoms calculated as O was 2.9 mass %. ２ It is presumed that the detected hydrogen atom content calculated as O was greater than the theoretical value for the same reason as in Example 1.

[0053] A lithium secondary battery was fabricated in the same manner as in Example 1, and charge / discharge evaluation was performed. As a result, when the titanate compound of this example was used, the initial discharge capacity was 308 mAh / g, and the discharge capacity at the 10th cycle was 280 mAh / g.

[0054] Example 3: TiO ２ (anatase, particle size: approximately 200 nm) and NaOH were dissolved and suspended in water in a molar ratio of 1:2, dried, and heated in air at 600°C for 12 hours to obtain α-Na ２ TiO ３ (Preparation step). ２ TiO ３The resulting sample was suspended in a 0.5 M aqueous HCl solution for 24 hours, filtered, and then dried (acid treatment step). The 2θ pattern of the thus obtained sample was measured by XRD in the same manner as in Example 1, and diffraction peaks were confirmed at 29.0° and 45.2° (Fig. 3, 3b).

[0055] Next, heat treatment was carried out in a vacuum at 260° C. for 5 hours to obtain a titanic acid compound of the present invention (heat treatment step). The obtained titanic acid compound was subjected to XRD 2θ pattern measurement. As a result, it was found that the titanic acid compound had a H ２ Ti １２ O ２５ It was confirmed that the above-mentioned fitting confirmed diffraction peaks at 14.4°, 28.7°, and 45.2°, but no clear diffraction peaks were confirmed in the ranges of 48.0° to 49.0° and 52.4° to 53.4° (Fig. 3, 3c). Therefore, in the XRD 2θ pattern, the ratio (B / A) of the maximum peak intensity B at 48.0° to 49.0° to the maximum peak intensity A at 44.7° to 45.7° was 0, and the ratio (C / A) of the maximum peak intensity C at 52.4° to 53.4° to the peak intensity A was also 0. Furthermore, thermogravimetry of the titanate compound obtained above was performed in the same manner as in Example 1, and the chemical composition was calculated. As a result, H ２ The content of hydrogen atoms calculated as O was 2.3 mass %. ２ It is presumed that the detected hydrogen atom content calculated as O was greater than the theoretical value for the same reason as in Example 1.

[0056] A lithium secondary battery was fabricated in the same manner as in Example 1, and charge / discharge evaluation was performed. As a result, when the titanate compound of this example was used, the initial discharge capacity was 294 mAh / g, and the discharge capacity at the 10th cycle was 284 mAh / g.

[0057] Example 4: TiO ２ (rutile, particle size: approximately 15 nm) and NaOH were dissolved and suspended in water in a molar ratio of 1:2, dried, and heated in air at 750°C for 12 hours to obtain β-Na ２ TiO３ (Preparation step). ２ TiO ３ The resulting sample was suspended in a 0.5 M aqueous HCl solution for 24 hours, filtered, and then dried (acid treatment step). The 2θ pattern of the thus obtained sample was measured by XRD in the same manner as in Example 1, and diffraction peaks were confirmed at 28.9° and 45.6° (FIG. 4B).

[0058] Next, heat treatment was carried out in a vacuum at 260° C. for 5 hours to obtain a titanic acid compound of the present invention (heat treatment step). The obtained titanic acid compound was subjected to XRD 2θ pattern measurement. As a result, it was found that the titanic acid compound had a H ２ Ti １２ O ２５ It was confirmed that the titanate compound was synthesized (4c in FIG. 4). The fitting confirmed diffraction peaks at 14.5°, 28.9°, and 45.2°, but no clear diffraction peaks were confirmed in the ranges of 48.0° to 49.0° and 52.4° to 53.4° (4c in FIG. 4). Therefore, in the XRD 2θ pattern, the ratio (B / A) of the maximum peak intensity B at 48.0° to 49.0° to the maximum peak intensity A at 44.7° to 45.7° was 0, and the ratio (C / A) of the maximum peak intensity C at 52.4° to 53.4° to the peak intensity A was also 0. Furthermore, thermogravimetry of the titanate compound obtained above was performed in the same manner as in Example 1, and the chemical composition was calculated. As a result, H ２ The content of hydrogen atoms calculated as O was 2.2 mass %. ２ It is presumed that the detected hydrogen atom content calculated as O was greater than the theoretical value for the same reason as in Example 1.

[0059] A lithium secondary battery was fabricated in the same manner as in Example 1, and charge / discharge evaluation was performed. As a result, when the titanate compound of this example was used, the initial discharge capacity was 269 mAh / g, and the discharge capacity at the 10th cycle was 260 mAh / g.

[0060] Example 5: TiO ２Rutile (particle size: about 15 nm) and NaOH were dissolved and suspended in water in a molar ratio of 5:8, dried, and heated in air at 600°C for 12 hours to obtain Na ８ Ti ５ O １４ (Preparation step). ８ Ti ５ O １４ The resulting sample was suspended in a 0.5 M aqueous HCl solution for 24 hours, filtered, and then dried (acid treatment step). The 2θ pattern of the thus obtained sample was measured by XRD in the same manner as in Example 1, and diffraction peaks were confirmed at 29.3° and 46.3° (Fig. 5b).

[0061] Next, heat treatment was carried out in a vacuum at 260° C. for 5 hours to obtain a titanic acid compound of the present invention (heat treatment step). The obtained titanic acid compound was subjected to XRD 2θ pattern measurement. As a result, it was found that the titanic acid compound had a H ２ Ti １２ O ２５ It was confirmed that the titanate compound was synthesized (5c in FIG. 5). The fitting confirmed diffraction peaks at 14.0°, 28.6°, and 45.1°, but no clear diffraction peaks were confirmed in the ranges of 48.0° to 49.0° and 52.4° to 53.4° (5c in FIG. 5). Therefore, in the XRD 2θ pattern, the ratio (B / A) of the maximum peak intensity B at 48.0° to 49.0° to the maximum peak intensity A at 44.7° to 45.7° was 0, and the ratio (C / A) of the maximum peak intensity C at 52.4° to 53.4° to the peak intensity A was also 0. Furthermore, thermogravimetry of the titanate compound obtained above was performed in the same manner as in Example 1, and the chemical composition was calculated. As a result, H ２ The content of hydrogen atoms calculated as O was 2.8 mass %. ２ It is presumed that the detected hydrogen atom content calculated as O was greater than the theoretical value for the same reason as in Example 1.

[0062] A lithium secondary battery was fabricated in the same manner as in Example 1, and charge / discharge evaluation was performed. As a result, when the titanate compound of this example was used, the initial discharge capacity was 285 mAh / g, and the discharge capacity at the 10th cycle was 265 mAh / g.

[0063] Example 6: TiO ２ (anatase, particle size: approximately 6 nm) and LiOH·H ２ O was dissolved and suspended in water at a molar ratio of 1:2, dried, and heated in air at 500°C for 12 hours to obtain cubic-Li. ２ TiO ３ (Preparation step, 8a in FIG. 8). ２ TiO ３ The resulting mixture was suspended in a 0.05 M aqueous HCl solution for 1 hour, filtered, and dried. The mixture was then heated in air at 300° C. for 5 hours, suspended in a 0.5 M aqueous HCl solution for 24 hours, filtered, and dried (acid treatment step).

[0064] Next, heat treatment was carried out in air at atmospheric pressure at 400°C for 5 hours to obtain the titanic acid compound of the present invention (heat treatment step). The obtained titanic acid compound was subjected to XRD 2θ pattern measurement, and as a result, it was found that the titanic acid compound of the present invention had a H ２ Ti １２ O ２５ It was confirmed that the titanate compound was synthesized (8c in FIG. 8). The XRD 2θ pattern of the sample thus obtained was measured, and diffraction peaks were confirmed at 14.7°, 29.0°, and 44.9° by the above-mentioned fitting (8b in FIG. 8). In the XRD 2θ pattern, the ratio (B / A) of the maximum peak intensity B at 48.0° to 49.0° to the maximum peak intensity A at 44.7° to 45.7° was 0, and the ratio (C / A) of the maximum peak intensity C at 52.4° to 53.4° to the peak intensity A was 0. Furthermore, thermogravimetry of the titanate compound obtained above was performed in the same manner as in Example 1, and the chemical composition was calculated. As a result, H ２ The hydrogen atom content calculated as O was 1.9 mass %.

[0065] A lithium secondary battery was fabricated in the same manner as in Example 1, and charge / discharge evaluation was performed. As a result, when the titanate compound of this example was used, the initial discharge capacity was 292 mAh / g, and the discharge capacity at the 10th cycle was 286 mAh / g.

[0066] Example 7 A titanic acid compound of the present invention was obtained in the same manner as in Example 6, except that a heat treatment was carried out in a vacuum at 425° C. for 5 hours to obtain a titanic acid compound (heat treatment step). The 2θ pattern of the obtained titanic acid compound was measured using XRD. As a result, similar to Example 1, ２ Ti １２ O ２５ It was confirmed that the titanate compound obtained above was synthesized (FIG. 9). The above-mentioned fitting confirmed diffraction peaks at 14.7°, 28.9°, and 45.0°. In the XRD 2θ pattern, the ratio (B / A) of the maximum peak intensity B at 48.0° to 49.0° to the maximum peak intensity A at 44.7° to 45.7° was 0, and the ratio (C / A) of the maximum peak intensity C at 52.4° to 53.4° to the peak intensity A was 0. Furthermore, thermogravimetry of the titanate compound obtained above was carried out in the same manner as in Example 1, and the chemical composition was calculated. As a result, H ２ The hydrogen atom content calculated as O was 1.7 mass %.

[0067] A lithium secondary battery was fabricated in the same manner as in Example 1, and charge / discharge evaluation was performed. As a result, when the titanate compound of this example was used, the initial discharge capacity was 275 mAh / g, and the discharge capacity at the 10th cycle was 282 mAh / g.

[0068] Example 8 A titanic acid compound of the present invention was obtained in the same manner as in Example 3, except that the heat treatment step was performed in air at atmospheric pressure at 280° C. for 5 hours to obtain a titanic acid compound (heat treatment step). The 2θ pattern of the obtained titanic acid compound was measured, and as a result, the H ２ Ti １２ O ２５It was confirmed that the titanate compound obtained above was synthesized (FIG. 10). The above-mentioned fitting confirmed diffraction peaks at 14.7°, 28.9°, and 45.2°. In the XRD 2θ pattern, the ratio (B / A) of the maximum peak intensity B at 48.0° to 49.0° to the maximum peak intensity A at 44.7° to 45.7° was 0.09, and the ratio (C / A) of the maximum peak intensity C at 52.4° to 53.4° to the peak intensity A was 0. Furthermore, thermogravimetry of the titanate compound obtained above was carried out in the same manner as in Example 1, and the chemical composition was calculated. As a result, H ２ The content of hydrogen atoms calculated as O was 3.5% by mass. ２ It is presumed that the detected hydrogen atom content calculated as O was greater than the theoretical value for the same reason as in Example 1.

[0069] A lithium secondary battery was fabricated in the same manner as in Example 1, and charge / discharge evaluation was performed. As a result, when the titanate compound of this example was used, the initial discharge capacity was 306 mAh / g, and the discharge capacity at the 10th cycle was 289 mAh / g.

[0070] Example 9 A titanic acid compound of the present invention was obtained in the same manner as in Example 3, except that in the acid treatment step, the compound was suspended in a 0.5 M HCl aqueous solution for 6 hours, and in the heat treatment step, the compound was heat-treated in air at atmospheric pressure at 300° C. for 5 hours. The 2θ pattern of the obtained titanic acid compound was measured, and as in Example 1, the H ２ Ti １２ O ２５ It was confirmed that the titanate compound obtained above was synthesized (FIG. 11). The above-mentioned fitting confirmed diffraction peaks at 14.5°, 29.0°, and 45.1°. In the XRD 2θ pattern, the ratio (B / A) of the maximum peak intensity B at 48.0° to 49.0° to the maximum peak intensity A at 44.7° to 45.7° was 0, and the ratio (C / A) of the maximum peak intensity C at 52.4° to 53.4° to the peak intensity A was 0. Furthermore, thermogravimetry of the titanate compound obtained above was carried out in the same manner as in Example 1, and the chemical composition was calculated. As a result, H２ The content of hydrogen atoms calculated as O was 2.6 mass %. ２ It is presumed that the detected hydrogen atom content calculated as O was greater than the theoretical value for the same reason as in Example 1.

[0071] A lithium secondary battery was fabricated in the same manner as in Example 1, and charge / discharge evaluation was performed. As a result, when the titanate compound of this example was used, the initial discharge capacity was 296 mAh / g, and the discharge capacity at the 10th cycle was 286 mAh / g.

[0072] Example 10: TiO ２ (anatase, particle size: approximately 200 nm) and NaOH were dissolved and suspended in water in a molar ratio of 1:2, dried, and heated in air at 750°C for 12 hours to obtain β-Na ２ TiO ３ (Preparation step). ２ TiO ３ The resulting mixture was suspended in a 0.5M aqueous HCl solution for 48 hours, filtered, and dried (acid treatment step). It was then heat-treated in air at 300°C for 5 hours, suspended in a 0.5M aqueous HCl solution for 24 hours, filtered, and dried to obtain a titanic acid compound of the present invention. The 2θ pattern of the obtained titanic acid compound was measured, and the results were the same as in Example 1. ２ Ti １２ O ２５ It was confirmed that the titanate compound obtained above was synthesized (FIG. 12). The above-mentioned fitting confirmed diffraction peaks at 14.6°, 28.9°, and 44.9°. In the XRD 2θ pattern, the ratio (B / A) of the maximum peak intensity B at 48.0° to 49.0° to the maximum peak intensity A at 44.7° to 45.7° was 0, and the ratio (C / A) of the maximum peak intensity C at 52.4° to 53.4° to the peak intensity A was 0. Furthermore, thermogravimetry of the titanate compound obtained above was carried out in the same manner as in Example 1, and the chemical composition was calculated. As a result, H ２ The content of hydrogen atoms calculated as O was 2.6 mass %. ２It is presumed that the detected hydrogen atom content calculated as O was greater than the theoretical value for the same reason as in Example 1.

[0073] A lithium secondary battery was fabricated in the same manner as in Example 1, and charge / discharge evaluation was performed. As a result, when the titanate compound of this example was used, the initial discharge capacity was 273 mAh / g, and the discharge capacity at the 10th cycle was 271 mAh / g.

[0074] Comparative Example 1: TiO ２ (Rutile) and Na ２ CO ３ from Na by solid phase method ２ Ti ３ O7 was obtained. ２ Ti ３ O7 was suspended in a 0.5 M aqueous HCl solution at 60°C for 3 days, filtered, and dried. The suspension was then heat-treated in air at 260°C for 5 hours to obtain a titanate compound. The resulting titanate compound was analyzed for its 2θ pattern by XRD, revealing diffraction peaks at 14.0°, 24.7°, 28.7°, 31.1°, 43.5°, 44.5°, 48.5°, 52.9°, and 57.7° (Figure 6). No diffraction peaks were observed in the XRD 2θ pattern between 44.7° and 45.7°. Taking into account measurement error, the maximum peak intensity at 44.5°, the 2θ peak closest to this range, was designated as peak intensity A. It was confirmed that the ratio (B / A) of the maximum peak intensity B at an angle of 48.0° or more and 49.0° or less to the peak intensity A was 1.07, and further that the ratio (C / A) of the maximum peak intensity C at an angle of 52.4° or more and 53.4° or less to the peak intensity A was 0.36.

[0075] A lithium secondary battery was fabricated in the same manner as in Example 1, and charge / discharge evaluation was performed. As a result, when the titanate compound of this example was used, the initial discharge capacity was 217 mAh / g, and the discharge capacity at the 10th cycle was 217 mAh / g.

[0076] Comparative Example 2: TiO ２ (anatase) and LiOH·H ２Cubic Lithium is synthesized from O by hydrothermal synthesis. ２ TiO3 was obtained. ２ TiO3 was suspended in water, filtered, dried, and then heat-treated in air at 300°C for 5 hours. This sample was then suspended in 0.5M HCl aqueous solution for 24 hours, filtered, and dried. The resulting titanate compound was then heat-treated in vacuum at 425°C for 5 hours to obtain a titanate compound. The XRD 2θ pattern of the resulting titanate compound showed diffraction peaks at 14.6°, 25.3°, 29.1°, 38.9°, 44.9°, 57.4°, and 66.1°, but no clear diffraction peaks were observed in the ranges of 48.0° to 49.0° and 52.4° to 53.4° (Figure 7). Therefore, in the XRD 2θ pattern, the ratio (B / A) of the maximum peak intensity B at 48.0° to 49.0° to the maximum peak intensity A at 44.7° to 45.7° was 0, and the ratio (C / A) of the maximum peak intensity C at 52.4° to 53.4° to the peak intensity A was 0. Furthermore, as a result of measuring the titanic acid compound using a thermogravimetric analyzer, it was confirmed that H ２ The hydrogen atom content calculated as O was 1.9 mass %.

[0077] A lithium secondary battery was fabricated in the same manner as in Example 1, and charge / discharge evaluation was performed. As a result, when the titanate compound of this example was used, the initial discharge capacity was 282 mAh / g, and the discharge capacity at the 10th cycle was 278 mAh / g.

[0078] (Comparative Example 3) Aggregated TiO ２ Rutile (particle size: approximately 15 nm) and NaOH were dissolved and suspended in water in a molar ratio of 1:2, dried, and heated in air at 800°C for 1 hour to obtain γ-Na ２ TiO ３ The main component is β-Na ２ TiO ３ Contains a small amount of γ-Na ２ TiO ３ (Preparation step, 13a in FIG. 13). ２ TiO ３The resulting sample was suspended in a 0.5 M aqueous HCl solution for 24 hours, filtered, and dried (acid treatment step). The XRD 2θ pattern of the sample thus obtained was measured, and a diffraction peak was confirmed at 29.4°, but no other clear peaks were observed (Fig. 13, 13b). The sample was then heat-treated in a vacuum at 260°C for 5 hours, revealing an anatase-type TiO ２ was obtained (FIG. 13, 13c).

[0079] From the results of the examples shown above, it is possible to obtain cubic-Li by the solid phase method as a starting material. ２ TiO ３ , α-Na ２ TiO ３ , β-Na ２ TiO ３ , and Na ８ Ti ５ O １４ It has been found that when a lithium secondary battery is fabricated using a titanate compound produced by a production method comprising the steps of: a preparation step of preparing at least one alkali metal titanium oxide selected from the group consisting of: an acid treatment step of acid-treating the alkali metal titanium oxide; and a heat treatment step of heat-treating the acid-treated compound, the lithium secondary battery has a high charge / discharge capacity and excellent charge / discharge characteristics.

[0080] The present invention may be embodied in the following manner: [1] A compound represented by the general formula H ｘ Ti ｙ O ｚ (x>0, y>0, z>0) as a starting material, a method for producing a titanic acid compound represented by the formula (1), ２ TiO ３ , α-Na ２ TiO ３ , β-Na ２ TiO ３ , and Na ８ Ti ５ O １４[2] A method for producing a titanic acid compound, comprising: a preparation step of preparing at least one alkali metal titanium oxide selected from the group consisting of: an acid treatment step of acid-treating the alkali metal titanium oxide; and a heat treatment step of heat-treating the acid-treated compound. [2] A method for producing a titanic acid compound according to [1], wherein the alkali metal titanium oxide after the acid treatment step has peaks in the 2θ pattern at 28.0° or more and 29.5° or less and 44.5° or more and 46.5° or less in the 2θ pattern obtained by X-ray diffraction measurement. [3] The solid-phase method in the preparation step is a method for producing a titanic acid compound according to [1], wherein the alkali metal titanium oxide after the acid treatment step has peaks in the 2θ pattern at 28.0° or more and 29.5° or less and 44.5° or more and 46.5° or less. ２ and an alkali metal hydroxide or a hydrate thereof, and then heating the mixture. [4] A method for producing a titanic acid compound according to [3], wherein the heating temperature in the solid phase method is 400°C or higher but lower than 800°C, and the heating time is 1 hour or longer. [5] A titanic acid compound obtained by the production method according to any one of [1] to [4], which is represented by the general formula H ２ Ti １２ O ２５ and having a particle size of 10 nm or more and 200 nm or less. [6] The titanate compound according to [5], wherein in a 2θ pattern of X-ray diffraction measurement, a ratio (B / A) of a maximum peak intensity B at 48.0° or more and 49.0° or less to a maximum peak intensity A at 44.7° or more and 45.7° or less is 0.5 or less. [7] The titanate compound according to [5] or [6], wherein in a 2θ pattern of X-ray diffraction measurement, a ratio (C / A) of a maximum peak intensity C at 52.4° or more and 53.4° or less to a maximum peak intensity A at 44.7° or more and 45.7° or less is 0.2 or less.

[0081] The titanate compound of the present invention can be used as an active material for the electrodes of lithium secondary batteries, and can achieve high charge / discharge capacities, and in this respect has high industrial applicability.

Claims

1. General formula H ｘ Ti ｙ O ｚ A method for producing a titanic acid compound represented by the formula (x>0, y>0, z>0), comprising: ２ TiO ３ , α-Na ２ TiO ３ , β-Na ２ TiO ３ , and Na ８ Ti ５ O １４ A method for producing a titanate compound, comprising: a preparation step of preparing at least one alkali metal titanium oxide selected from the group consisting of: an acid treatment step of treating the alkali metal titanium oxide with an acid; and a heat treatment step of heat treating the acid-treated compound.

2. The method for producing a titanic acid compound according to claim 1, wherein the alkali metal titanium oxide after the acid treatment step has peaks in the 2θ pattern of X-ray diffraction measurement at 28.0° or more and 29.5° or less and 44.5° or more and 46.5° or less.

3. The solid phase method in the preparation step is ２ The method for producing the titanate compound according to claim 1 , comprising mixing and then heating an alkali metal hydroxide.

4. The method for producing a titanic acid compound according to claim 3, wherein the heating temperature in the solid phase method is 400° C. or higher and lower than 800° C., and the heating time is 1 hour or longer.

5. A titanic acid compound obtained by the method according to any one of claims 1 to 4, which is represented by the general formula H ２ Ti １２ O ２５ and having a particle size of 10 nm or more and 200 nm or less.

6. The titanate compound according to claim 5, wherein in a 2θ pattern of an X-ray diffraction measurement, the ratio (B / A) of the maximum peak intensity B in the range of 48.0° to 49.0° to the maximum peak intensity A in the range of 44.7° to 45.7° is 0.5 or less.

7. The titanate compound according to claim 5, in which in a 2θ pattern of an X-ray diffraction measurement, the ratio (C / A) of the maximum peak intensity C in the range of 52.4° to 53.4° to the maximum peak intensity A in the range of 44.7° to 45.7° is 0.2 or less.

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