JPWO2019058822A1 - Titanium oxide and its manufacturing method, as well as electrode active materials and power storage devices using the titanium oxide. - Google Patents

Abstract

A new titanium oxide that can be used as an electrode material for lithium secondary batteries, which has an excellent long-term charge / discharge cycle and can be expected to have a high capacity, a manufacturing method thereof, and a storage capacity containing an electrode containing the titanium oxide as an active material as a constituent member. Provide a device. It is solved by a novel titanium oxide containing H having a characteristic local structure and having a characteristic vibration of the Ti-O-Ti skeleton and a method for producing the same.

Description

The present invention relates to a novel sodium titanate hydrate having a novel structure and a novel titanium oxide obtained by heat-treating a proton exchanger thereof. Further, the present invention relates to an electrode active material using these titanium oxides and a storage device thereof.

Currently, in Japan, most of the secondary batteries installed in portable electronic devices such as mobile phones and laptop computers are lithium secondary batteries. In addition, lithium secondary batteries are expected to be put into practical use as large batteries for hybrid cars, power load leveling systems, etc. in the future, and their importance is increasing.

The main components of this lithium secondary battery are a positive electrode and a negative electrode containing a material capable of reversibly occluding and releasing lithium, and a separator or a solid electrolyte containing a non-aqueous electrolyte solution.

Among these components, lithium cobalt oxide (LiCoO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), and lithium titanium acid (Li ₄ Ti ₅ O ₁₂ ) are being studied as active materials for electrodes. ), Metallic materials such as metallic lithium, lithium alloys, and tin alloys, and carbon-based materials such as graphite and MCMB (mesocarbon microbeads).

For these materials, the voltage of the battery is determined by the difference in chemical potential in the lithium content in each active material, but the ability to form a large potential difference, especially by combination, is a lithium secondary battery with excellent energy density. It is a feature of.

In particular, in the combination of lithium cobalt oxide LiCoO ₂ active material and carbon material as electrodes, a voltage close to 4V is possible, the charge / discharge capacity (the amount of lithium that can be detached / inserted from the electrodes) is large, and safety is also improved. Due to its high price, this combination of electrode materials is widely used in current lithium batteries.

On the other hand, the combination of an electrode containing a spinel-type lithium manganese oxide (LiMn ₂ O ₄ ) active material and a spinel-type lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ) active material causes a lithium occlusion / desorption reaction. It has been clarified that a lithium secondary battery having an excellent long-term charge / discharge cycle is possible because it is easy to carry out smoothly and the change in crystal lattice volume due to the reaction is small, and it has been put into practical use. ..

In the future, it is predicted that chemical batteries such as lithium secondary batteries and capacitors will require large-sized and long-life batteries such as automobile power supplies, large-capacity backup power supplies, and emergency power supplies. A combination of such oxide active materials requires a higher performance (large capacity) electrode active material.

Of these, the titanium oxide-based active material has a voltage of about 1 to 2 V when a lithium metal is used as the counter electrode. Therefore, as a material for the negative electrode, a material having various crystal structures is an electrode active material. The possibility of being examined.

Spinel-type lithium titanium oxide Li ₄ Ti ₅ O ₁₂ and titanium dioxide having a sodium bronze-type crystal structure (in the present specification, "titanium dioxide having a sodium bronze-type crystal structure" is referred to as "TIO ₂ (B)". _{abbreviated), a x H y Ti 1.73} O z (a is an alkali metal except _{lithium), TiO 2 · (H 2} O) a · (a 2 O) b (a is Na or K), Ti- H ₂ Ti ₁₂ O _25, which is a titanium oxide containing H in its composition, such as an OH-based titanium structure, and titanium oxide containing an H element in its crystal structure (in this specification, "H ₂ Ti ₁₂ O ₂₅ "). (Abbreviated as "HTO"), active materials such as monoclinic titanium-niobium composite oxides are attracting attention as electrode materials. (Patent Document 1-2, Non-Patent Document 1-2)

However, the theoretical capacity of Li ₄ Ti ₅ O ₁₂ is about 175 mAh / g, and it is not expected to increase the capacity. Some titanium oxides containing TiO ₂ (B) and H in the composition have been synthesized and have an initial charge capacity exceeding 300 mAh / g, but have a problem that the initial irreversible capacity is large. Regarding HTO, the initial irreversible capacity is smaller than that of TiO ₂ (B), but the initial charge capacity is about 230 mAh / g, and it is said that the irreversible capacity will increase although the capacity can be further increased by miniaturization. I have a problem. Some monoclinic titanium niobium composite oxides have an initial charge capacity of about 280 mAh / g and a relatively small irreversible capacity, but the price of niobium (about 6 times as of 2007) and the amount of resources compared to titanium. It has a problem in that it (220 times the existence ratio in the crust).

Therefore, it is desired to introduce a new titanium oxide that overcomes these problems, has a small initial negative irreversible capacity, a large charge / discharge capacity, is expensive, and does not contain an element having a problem in the amount of resources.

Japanese Unexamined Patent Publication No. 2014-186826 Japanese Unexamined Patent Publication No. 2008-255000

A. R. Armstrong, G. Armstrong, J. Canales, R. Garcia, P. G. Bruce, Advanced Materials, 17, 862-865 (2005) J. Akimoto, K. Chiba, N. Kijima, H. Hayakawa, S. Hayashi, Y. Gotoh, Y. Idemoto, Journal of The Electrochemical Society, 158, A546-A549 (2011)

An object of the present invention is to provide a novel titanium oxide and a method for producing the same, as well as an electrode active material and a power storage device using the titanium oxide, which solve the above-mentioned current problems.

As a result of diligent studies, the present inventor has made a titanium oxide containing H having a characteristic local structure different from that of titanium oxide containing H such as HTO, and having a characteristic Ti-O-Ti skeleton vibration. The present invention was completed by finding that

That is, the present invention provides a novel titanium oxide having a novel structure shown below and a method for producing the same, and provides an electrode active material using these titanium compounds and a storage device thereof.
(1) In ¹ H solid-state NMR measurement containing H, the peak top is 9-11 ppm (peak 1) when the spectrum obtained from a sample at room temperature rotated 1000 to 12500 rpm is peak-separated using an electromagnetic wave of 400 MHz. ) And 6.7-8 ppm (peak 2), and the peak intensity ratio (I _{peak 1} / I _{peak 2} ) of these _{two peaks} is 1.0 or less.
(2) The titanium oxide according to (1), wherein the titanium oxide has an absorption peak at 930 to 990 cm ^-1 in infrared absorption analysis.
(3) In the powder X-ray diffraction pattern in which the titanium oxide is a source of CuKα, the peak half width of the peak existing at 2θ = 24.2 to 25.2 ° and 47.9 to 48.6 ° is The titanium oxide according to (1) or (2), which is 0.5 to 2 ° and 0.25 to 1 °, respectively.
(4) The method for producing a titanium oxide according to any one of (1) to (3), which is a hydrothermal synthesis method using a solution in which a titanium source and a sodium source are dissolved or suspended. A step of synthesizing a Japanese product, a step of synthesizing a proton exchanger of the sodium titanate hydrate, and a heat treatment of the proton exchanger of the sodium titanate hydrate in an oxygen gas-containing atmosphere or an inert gas atmosphere. A method for producing a titanium oxide having a process and.
(5) The sodium titanate hydrate has 2θ = 10.1 to 10.5 °, 15.4 to 15.8 °, and 24.7 to 25 in a powder X-ray diffraction pattern using CuKα as a radiation source. It has at least peaks at positions of .1 °, 29.4 to 29.8 °, and 48.2 to 48.6 °, and the above 2θ = 24.7 to 25.1 ° and 29.4 to 29.8 °. , The method for producing a titanium oxide according to (4), wherein the peak half-value widths of the peaks existing at 48.2 to 48.6 ° are 0.8 ° or less, respectively.
(6) The peak top of the sodium titanate hydrate when the spectrum obtained from a sample at room temperature rotated at 1000 to 12,500 rpm using an electromagnetic wave of 400 MHz was peak-separated in ¹ H solid-state NMR measurement was 11. The method for producing a titanium oxide according to (4) or (5), which is present at 4 to 12.7 ppm and 6.4 to 7.6 ppm.
(7) An electrode active material containing the titanium oxide according to any one of (1) to (3) above.
(8) A power storage device using the electrode active material according to (7) above.

According to the present invention, a titanium oxide containing H having a characteristic local structure different from that of titanium oxide containing H such as HTO and having a characteristic vibration of the Ti-O-Ti skeleton can be produced. ..
This titanium oxide is useful in various applications. For example, when used as an electrode active material, it can provide a lithium secondary battery having an excellent long-term charge / discharge cycle and a high capacity.

It is a synthesis flow chart of a novel titanium oxide. It is the elemental analysis result by the characteristic X-ray measurement of the sample A. It is the FT-IR absorption spectrum measurement result of the sample A. This is the result of thermogravimetric analysis of sample A. It is a powder X-ray diffraction measurement result of the sample A. Is a ¹ H solid state NMR spectrum measurements of the sample A. It is the elemental analysis result by the characteristic X-ray measurement of the sample A'. It is the FT-IR absorption spectrum measurement result of the sample A'. It is a thermogravimetric analysis result of the sample A'. It is a powder X-ray diffraction measurement result of the sample A'. Is a ^{1 H} solid state NMR spectrum measurements of the sample A '. It is the elemental analysis result by the characteristic X-ray measurement of sample A ". It is the FT-IR absorption spectrum measurement result of sample A ”and sample B. It is a thermogravimetric analysis result of sample A ”and sample B. It is the powder X-ray diffraction measurement result of sample A ”and sample B. Is a ¹ H solid state NMR spectrum measurements of the sample A "and Sample B. It is a basic structure diagram of a lithium secondary battery (coin type cell). This is the charge / discharge characteristic when sample A ”and sample B are used as negative electrodes. It is the powder X-ray diffraction measurement result of the sample C. It is the powder X-ray diffraction measurement result of the sample C ". It is a powder X-ray diffraction measurement result of sample D. It is a powder X-ray diffraction measurement result of sample D'and sample D'. It is a powder X-ray diffraction measurement result of sample E. It is the powder X-ray diffraction measurement result of the sample F. It is a powder X-ray diffraction measurement result of the sample G. It is a powder X-ray diffraction measurement result of sample A "-2. It is a powder X-ray diffraction measurement result of sample A "-3. It is the powder X-ray diffraction measurement result of the sample H. It is the powder X-ray diffraction measurement result of the sample H ". It is a powder X-ray diffraction measurement result of sample I. This is the powder X-ray diffraction measurement result of Sample I ”.

As shown in the synthetic flow chart of FIG. 1, the novel titanium oxide of the present embodiment is synthesized by synthesizing a novel sodium titanate hydrate, and ion exchange and heat treatment thereof.
The characteristics and production method of the novel titanium oxide and the novel sodium titanate hydrate which is a precursor thereof according to the present embodiment will be described in more detail.

(Characteristics of new titanium oxide)
The novel titanium oxide of the present embodiment contains H and peaks when the spectrum obtained from a sample at room temperature rotated 1000 to 12,500 rpm is peak-separated using an electromagnetic wave of 400 MHz in ¹ H solid-state NMR measurement. The top is present at 9-11 ppm (peak 1) and 6.7-8 ppm (peak 2), and the peak intensity ratio (I _{peak 1} / I _{peak 2} ) of these _{two peaks} is 1.0 or less. And.
Usually, ¹ H solid-state NMR signals are represented by overlapping ¹ H signals with individual local structures. Therefore, by separating the signal into a plurality of peaks, it is possible to distinguish ¹ H having a different local structure (for example, water contained in adsorption or between layers or H having a different occupied site in the crystal structure). It is also known that there is a correlation between the strength of hydrogen bonds of H in the crystal structure and the peak position (for example, Solid State Oxygens, Vol. 177 (2006) 3223-3231), and H at a low peak position. The hydrogen bond with the oxygen atom in the vicinity becomes weaker. This means that H acts to strengthen the bond with O, which is directly covalently bonded, so that H is less likely to dissociate as H ⁺ . H ⁺ causes side reactions such as decomposition of the organic electrolyte used in lithium-ion batteries, so it is better to reduce it as much as possible. From this point of view, H contained in the new titanium oxide has a large proportion of those showing a low peak position.
In peak separation, generally, multiple peaks having shapes such as Lorentz type distribution and Gauss type distribution are set, and the peak position and the peak position are set so that the total peak intensity of each signal deviates from the original measurement result to the minimum. Fitting is performed by changing the peak intensity and half width, and peak separation is performed. The number of peak separations is the number of ¹ H local structures that are assumed to exist, and since the ¹ H local structure determines the approximate range of peak positions, limits the peak positions and full width at half maximum are set during fitting. Sometimes.

Further, the titanium oxide is characterized by having vibration absorption different from that of a typical titanium oxide in infrared absorption analysis, and is characterized by having an absorption peak at 930 to 990 cm ^-1 .
Usually, the titanium oxide appears stretching vibration by Ti-O-Ti skeleton around 500～1000Cm ^-1, in the rutile or anatase which is a typical titanium oxide, broad absorption spectrum is observed near 700 cm ^-1. When the crystal structure of titanium oxide is different or when different elements are bonded to the Ti-O-Ti skeleton, the bond strength of the Ti-O-Ti bond changes, so the absorption peak position changes or new Absorption peak appears. When a light atom such as H is bonded, the peak generally shifts to the high frequency side. In HTO disclosed in Non-Patent Document 2, the absorption spectrum by stretching vibration of Ti-O-Ti backbone absorption spectrum and 760 cm ^-1 and 910 cm ^-1 due to the stretching vibration of the OH groups to 3,447 cm ^-1 was observed, Ti As a result of the OH group being bonded to a part of the -O-Ti skeleton, the absorption spectrum of the Ti-O-Ti skeleton due to the expansion and contraction vibration is shifted to the high frequency side, and a new absorption peak appears. Since more water than HTO is desorbed from the weight reduction by TG-DTA measurement, the titanium oxide of the present embodiment is considered to have a high bond ratio of OH groups to the Ti-O-Ti skeleton, and has a higher wave. It is thought that it will shift to the number side.

Further, the titanium oxide has peak half widths of peaks existing at 2θ = 24.2 to 25.2 ° and 47.9 to 48.6 ° by powder X-ray diffraction using CuKα as a radiation source, respectively. It is characterized in that it is 0.5 to 2 ° and 0.25 to 1 °, preferably 0.6 to 1.4 ° and 0.3 to 0.5 °, respectively.
Normally, in powder X-ray diffraction of a crystalline compound, a peak appears at a position of 2θ value depending on the crystal structure of the sample, but the peak appears due to nanonization of the sample, inhibition of crystal growth, deterioration of crystallinity due to pulverization, etc. Wider width affects sample characteristics. Since the titanium oxide is synthesized while partially maintaining the layered structure of the precursor, crystal growth is inhibited, the crystallite diameter remains small, and the peak width is widened. In particular, in the HTO, it is reported that the peaks of 2θ = 24.2 to 25.2 ° and 47.9 to 48.6 ° correspond to the (110) plane and the (020) plane, respectively (for example, Materials Letters, Vol. 143 (2015) 101-104), tunnel structures suitable for insertion and desorption of Li ⁺ are formed in the [110] and [010] directions (for example, Journal of the Ceramic Society of Japan, Vol.124 (2016) 710-713). Since the novel titanium oxide of the present embodiment shows a powder XRD pattern similar to that of HTO, it is considered to have a similar crystal structure, and the wide peak width of these has many corresponding surfaces. That is, it has more surfaces suitable for inserting / removing Li ⁺ , which is desirable from the viewpoint of powder utilization efficiency. The spread of the peak width is expressed using the peak half-value width (total width at a height of 1/2 of the peak height), and is used when determining crystallinity and crystallite diameter.

(Production method of new sodium titanate hydrate)
In the production method of the present embodiment, first, sodium titanate hydrate having high crystallinity is produced.
The titanium raw material is not particularly limited as long as it contains titanium, for example, titanium (metal titanium) and oxides such as TiO, Ti ₂ O ₃ , TiO ₂ , TiO (OH) ₂ , TiO ₂ · xH. Examples include titanium oxide hydrate represented by ₂ O (x is optional), inorganic titanium compounds such as titanium chloride and titanium sulfate, and organic titanium compounds such as titanium isopropoxide and titanium butoxide. Among these, are preferred in particular titanium oxide or titanium oxide hydrate, TiO _{(OH) 2} or orthotitanate represented by metatitanic acid and _{TiO 2} · 2H 2 O represented by _{TiO 2} · _H 2 O or, A mixture thereof and the like can be used.

As the sodium raw material, at least one of sodium (metallic sodium) and a sodium compound is used. The sodium compound is not particularly limited as long as it contains sodium, for example, oxides such as Na ₂ O and Na ₂ O ₂ , salts such as Na ₂ CO ₃ and Na NO ₃ , hydroxides such as NaOH, and the like. Can be mentioned. In addition, the sodium raw material includes metals such as lithium and potassium, which are the same alkali metals, lithium compounds (for example, Li ₂ O, Li ₂ CO ₃ , Li NO ₃ , Li OH, etc.), and potassium compounds (for example, K ₂ O, K _2). (CO ₃ , KNO ₃ , KOH, etc.) may be mixed, and the sodium raw material may exceed 50% in terms of molar ratio. Of these, NaOH is particularly preferable. Furthermore, since the sodium raw material also has a function of promoting the dissolution of the titanium raw material during synthesis, it is necessary to add it in excess to the titanium raw material. For example, when TiO ₂ is used as a titanium raw material, when NaOH is selected as a sodium raw material, the weight ratio is preferably 8 times or more.

First, these are dissolved or suspended in water or ethanol or a mixture thereof as a solvent and mixed well. Mixing is carried out at room temperature to below the boiling point of the solvent. At this time, in order to increase the reactivity encourage dissolution and complexation of titanium raw material, hydrogen peroxide and ammonia, NH ₄ F, or the like may be added glucose. In addition, various surfactants and inorganic and organic salts such as sodium sulfate may be added in order to improve the dispersibility and control the morphology during crystal growth. Further, carbon particles, carbon nanotubes, graphene, graphene oxide and the like may be added in an amount of 0.1 wt% to 10 wt% in order to impart conductivity, and these may be compounded with the starting material in advance.

At this stage, in most cases, only a mixture of raw materials or a compound with extremely low crystallinity is obtained. Therefore, in order to obtain highly crystalline sodium titanate hydrate, it is necessary to carry out crystal growth in addition to the reaction of the raw materials. As such a synthesis method, a hydrothermal synthesis method is particularly preferable. In the hydrothermal synthesis method, the reaction temperature and time are not particularly limited as long as sufficient reaction and crystal growth can be performed, but the reaction temperature is preferably 190 ° C. or higher and the reaction time is preferably 10 hours or longer.

The desired chemical composition and crystallinity of the novel sodium titanate hydrate here can provide a compound showing an X-ray diffraction pattern similar to the X-ray diffraction pattern peculiar to the sodium titanate hydrate described above. It suffices if it has a certain degree of crystallinity. Further, a dispersion / atomization operation such as pulverization may be performed as long as the crystallinity above a certain level is not impaired.
The shape of the novel sodium titanate hydrate is not particularly limited, and may be an anisotropic shape such as a needle shape, a rod shape, a columnar shape, a spindle shape, a tubular shape, or a fibrous shape, or a spherical shape or an amorphous shape. Further, these particles may be granulated by a known method such as a spray dryer.

(Method for Producing Proton Exchanger of New Sodium Titanate Hydrate)
By applying the proton exchange reaction in an acidic aqueous solution using the novel sodium titanate hydrate obtained above as a starting material, almost all of the sodium titanate hydrate in the starting material compound is exchanged with hydrogen. A proton exchanger of sodium acid hydrate is obtained.
In this case, it is preferable that the sodium titanate hydrate obtained as described above is dispersed in an acidic aqueous solution, held for a certain period of time, and then dried. As the acid to be used, an aqueous solution containing at least one of hydrochloric acid, sulfuric acid, nitric acid and the like having an arbitrary concentration is preferable. Of these, it is preferable to use dilute hydrochloric acid having a concentration of 0.1 to 1.0 N. The treatment time is 10 hours to 10 days, preferably 1 to 7 days. Further, in order to shorten the treatment time, it is preferable to replace the solution with a new one as appropriate. Further, the exchange reaction treatment temperature may be room temperature (20 ° C.) or higher and lower than 100 ° C. A known drying method can be applied to the drying, but vacuum drying or the like is more preferable.

In the proton exchanger of sodium titanate hydrate obtained in this way, Na could not be detected by analysis in the solid state using an energy dispersive X-ray spectrometer, and the conditions of the exchange process were optimized. By doing so, it is possible to reduce the amount of sodium remaining from the starting material to below the detection limit of chemical analysis by the wet method.

(Manufacturing method of new titanium oxide)
Desirable dehydration by heat treatment using the proton exchanger of sodium titanate hydrate obtained above as a starting material in an oxygen gas-containing atmosphere such as air or in an inert gas atmosphere such as nitrogen or argon. By causing the reaction, titanium oxide is obtained. Further, the dehydration reaction can be promoted by reducing the pressure or vacuuming the above atmosphere. The heat treatment temperature is in the range of 250 ° C to 500 ° C, preferably 260 ° C to 400 ° C. The treatment time is usually 0.5 to 100 hours, preferably 1 to 30 hours, and the higher the treatment temperature, the shorter the treatment time can be.

(Characteristics of new sodium titanate hydrate)
The novel sodium titanate hydrate of the present embodiment has 2θ = 10.1 to 10.5 °, 15.4 to 15.8 °, and 24.7 to 2θ = 10.1 to 10.5 ° in a powder X-ray diffraction pattern using CuKα as a radiation source. It has at least peaks at 25.1 °, 29.4 to 29.8 °, and 48.2 to 48.6 °, and 2θ = 24.7 to 25.1 ° and 29.4 to 29.8. It is characterized in that the peak half-value widths of the peaks existing at ° and 48.2 to 48.6 ° are 0.8 ° or less, respectively.
The sodium titanate hydrate described above is a crystalline compound having a layered structure. Normally, a crystalline compound having a layered structure has an interlayer distance longer than the Ti-O atom distance of crystals such as rutile and anatase, and the crystal structure is stabilized by containing sodium ions, water, etc. between these layers. ing. Since these sodium ions and water are relatively loosely bonded, when the crystallinity is high, the sodium ion can be replaced with another ion by ion exchange or reversibly while maintaining the layered structure. Water can be taken in and out. In the case of this embodiment, Na ⁺ / H ⁺ ion exchange is performed using an acidic aqueous solution while maintaining the layered structure. When this ion exchanger is heat-treated, the dehydration reaction proceeds with the layered structure partially maintained, so the distance between Ti-O atoms becomes longer than that of typical titanium oxides such as rutile and anatase. It is a titanium oxide having the characteristics of the embodiment. On the other hand, even if it has a similar powder X-ray diffraction pattern, when sodium titanate hydrate having a wide peak half-value width, that is, low crystallinity is used, the crystal structure is not developed, so Na ⁺ / When H ⁺ ion exchange is performed, the layered structure cannot be maintained and the crystal structure collapses, and the titanium oxide obtained by heat treatment is mainly composed of typical titanium oxides such as anatase and rutile.

Further, the sodium titanate hydrate had a peak top of 11. when the spectrum obtained from a sample at room temperature rotated at 1000 to 12500 rpm was peak-separated using an electromagnetic wave of 400 MHz in ¹ H solid-state NMR measurement. It is characterized by being present at 4 to 12.7 ppm and 6.4 to 7.6 ppm.
Usually, the signal of NMR is to be displayed by the overlap of the ¹ H signals with individual local structure, also vary according to the moisture content of the sample. Therefore, by separating the signal into a plurality of peaks, it is possible to distinguish ¹ H having a different local structure (for example, ¹ H having different adsorption or water content between layers or ¹ H having different occupied sites in the crystal structure). ..
In peak separation, generally, multiple peaks having shapes such as Lorentz type distribution and Gauss type distribution are set, and the peak position and the peak position are set so that the total peak intensity of each signal deviates from the original measurement result to the minimum. Fitting is performed by changing the peak intensity and half width, and peak separation is performed. The number of peak separations is the number of ¹ H local structures that are assumed to exist, and since the ¹ H local structure determines the approximate range of peak positions, limits the peak positions and full width at half maximum are set during fitting. Sometimes.

(Lithium secondary battery)
The lithium secondary battery (storage device) according to the present embodiment uses the electrode containing the electrode active material containing the titanium oxide as a constituent member. That is, except that the titanium oxide active material of the present embodiment is used as one of the electrode materials, the battery elements of known lithium secondary batteries (coin type, button type, cylindrical type, all-solid type, etc.) are adopted as they are. Can be done.
FIG. 17 is a schematic view showing an example in which the lithium secondary battery according to the present embodiment is applied to a coin-type battery. The coin-type battery 1 is composed of a negative electrode terminal 2, a negative electrode 3, (separator + electrolytic solution) 4, an insulating packing 5, a positive electrode 6, and a positive electrode can 7.

In a lithium secondary battery, an electrode mixture is prepared by blending a conductive agent, a binder, etc. with the active material containing titanium oxide as necessary, and the electrode mixture is pressed against a current collector to form an electrode. Can be made. As the current collector, a stainless mesh, aluminum foil, or the like can be preferably used. As the conductive agent, acetylene black, Ketjen black or the like can be preferably used. As the binder, tetrafluoroethylene, polyvinylidene fluoride or the like can be preferably used.

The composition of the electrode active material, the conductive agent, the binder, etc. in the electrode mixture is not particularly limited, but usually the conductive agent is about 1 to 30% by weight (preferably 5 to 25% by weight), and the binder is. It may be 0 to 30% by weight (preferably 3 to 10% by weight), and the balance may be used as an electrode active material.

In the lithium secondary battery, as the counter electrode to the electrode, a known one that functions as a negative electrode and occludes lithium, such as metallic lithium or a lithium alloy, can be adopted. Alternatively, as a counter electrode, known ones such as lithium cobalt oxide (LiCoO ₂ ) and spinel-type lithium manganese oxide (LiMn ₂ O ₄ ) that function as a positive electrode and occlude lithium can also be adopted. .. That is, depending on the electrode constituent material to be combined, the electrode containing the electrode active material of the present embodiment can function as both a positive electrode and a negative electrode.

Further, in the lithium secondary battery of the present embodiment, known battery elements may be adopted for the separator, the battery container and the like.

Further, as the electrolyte, a known electrolyte, a solid electrolyte, or the like can be applied. For example, as the electrolytic solution, an electrolyte such as lithium perchlorate or lithium hexafluorophosphate is used as a solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate (PC), and diethyl carbonate (DEC). The dissolved one can be used.

Examples are shown below to further clarify the features of the present invention. The present invention is not limited to these examples.

Example 1
(Production method of new sodium titanate hydrate)
² g of titanium dioxide (crystal form: anatase, specific surface area: 280 m ² / g) was mixed with 20 g of sodium hydroxide and 50 ml of distilled water, and sealed in a hydrothermal synthesis container with a Teflon® liner having an internal volume of 100 ml. .. This was placed in a constant temperature bath, the temperature was raised from room temperature to 200 ° C. in 1 hour, and then held for 24 hours for hydrothermal synthesis. After completion of the synthesis, the mixture was naturally cooled to room temperature in a constant temperature bath. After cooling, the sample was taken out from the hydrothermal synthesis container together with the solution, and the solid content was separated and collected by suction filtration using a membrane filter (pore diameter: 0.2 μm). The recovered solid content was once dispersed in ion-exchanged water using an ultrasonic cleaner for cleaning, and suction filtration was performed again using a membrane filter. The recovered solid content was dried in a dryer at 70 ° C. for a whole day and night, and the agglutinate was lightly crushed in an agate mortar to obtain Sample A.

(Analysis of novel sodium titanate hydrate)
The sample A thus obtained was found to contain Na, Ti, and O as constituent elements by elemental analysis by characteristic X-ray measurement using the energy dispersive X-ray spectroscope of FIG. 2 (Fig. 2). C is derived from double-sided tape or carbon conductive film deposition). In addition, in the absorption spectrum measurement by FT-IR in FIG. 3, a broad absorption peak was observed near 3120 cm ^-1 (arrow in FIG. 3), and it was found that the sample A had an OH group. It was. Furthermore, the thermogravimetric analysis of FIG. 4 showed weight loss and endothermic reaction due to heating from room temperature to around 200 ° C., indicating that the adsorbed water and the water incorporated in the layers and crystal structure were desorbed. all right. The weight loss when heated to 600 ° C. where there was almost no change in weight was 10.13 wt%. From these results, it was clarified that Sample A was sodium titanate hydrate.
As shown in FIG. 5, sample A was subjected to powder X-ray diffraction using CuKα as a radiation source, and 2θ = 10.42 ° (peak 1), 15.68 ° (peak 2), and 24.96 ° (peak 3). ), 29.68 ° (peak 4), 48.44 ° (peak 5) had at least a peak. When compared with the powder X-ray diffraction results of typical sodium titanate hydrate, the results are as shown in Table 1. No sodium titanate hydrate satisfying all of the above peaks was found, and new sodium titanate was found. It turned out to be a hydrate. Further, as shown in Table 2, the peak half widths of the peaks 3 to 5 were 0.23 °, 0.40 °, and 0.23 °, respectively.

The analysis by ^{1 H} solid NMR of the sample A was carried out at room temperature using a Bruker NMR AVANCEIII 400WB. The signal pattern obtained was different as shown in Fig. 6 depending on the dry state of the sample before analysis. As the drying temperature increased, the signal around 5.3 ppm rapidly decreased, and the signal around 13.1 ppm moved to the lower side of the chemical shift. From this fact, around 5.3ppm and 13.1ppm is the signal of the ¹ H solid state NMR with water that has entered the adsorbed water and interlayer, the other is the specimen A native of the ¹ H solid state NMR signal. In addition to the above, the sample dried at 110 ° C. showed signal peaks at 12.03 ppm, 7.04 ppm, and 1.74 ppm. A signal is observed near 1.7 ppm of chemical shift in all measurements, but this is derived from the measuring container made of ZrO ₂ , and when measured only with the measuring container, the signal is at the position of 1.68 ppm of chemical shift. Appeared. ^{Incidentally,} the calibration of the chemical shift value of the ¹ H solid NMR is combined carbonyl group of glycine 176.48Ppm.
Although it is possible to obtain the original of the ^{1 H} solid NMR signals sample by sufficiently drying, which because itself is indicated by the superposition of the ¹ H solid NMR signals with different local structures, precisely the individual signals Peak separation was performed to understand. The peak of the Lorentzian distribution with five ^settings, 1.68Ppm you know the origin of the ¹ H, 5.3 ppm, the signals near 13.1ppm limited the range of variation of the peak position when fitted to ± 0.05 ppm .. The half width of each peak was set to 2 ppm or less. ¹ three samples with different dry H solid NMR measurement results of peak separation for, could be separated into five peaks as shown in FIG. Peak position after peak separation is as shown in each of Tables 3, peaks b and c were a ¹ H solid NMR signal derived from the sample.

(Manufacturing method of new sodium titanate ion exchanger)
Approximately 1 g of Sample A was suspended in 100 mL of a 0.5 mol / L hydrochloric acid aqueous solution at room temperature of 25 ° C., stirred with a Teflon-processed magnet stirrer for 12 hours, and then allowed to stand for 12 hours to allow the solid matter to settle and become a supernatant. The liquid was removed. A fresh 0.5 mol / L hydrochloric acid aqueous solution was added to the remaining solid content to 100 mL, and the same operation was performed twice more. Finally, the solid content was suction-filtered with a membrane filter (pore diameter: 0.2 μm) while rinsing with ion-exchanged water. At this stage, the solid content was washed with ion-exchanged water a plurality of times, the solid content was placed on a petri dish while adhering to the filter, placed in a dryer at 60 ° C., and dried for 24 hours to obtain Sample A'.

(Analysis of ion exchanger of novel sodium titanate hydrate)
The sample A'obtained in this way was found to contain Ti and O as constituent elements by elemental analysis by characteristic X-ray measurement using the energy dispersive X-ray spectrometer shown in FIG. 7, and Na was Since it could not be confirmed, it was found that Na ⁺ / H ⁺ ion exchange was performed. In addition, in the absorption spectrum measurement by FT-IR in FIG. 8, a broad absorption peak was observed near 3130 cm ^-1 (arrow in FIG. 8), and from this, it is possible that the sample A'has an OH group. all right. Furthermore, the thermogravimetric analysis of FIG. 9 showed that weight loss and endothermic reaction due to heating from room temperature to around 200 ° C. were observed, and that adsorbed water and water incorporated in the layers and crystal structure were desorbed. all right. The weight loss when heated to 600 ° C. where there was almost no change in weight was 15.53 wt%.
Sample A'shows a pattern as shown in FIG. 10 by powder X-ray diffraction using CuKα as a radiation source, and has a sharp peak at the position of 2θ = 10.97 °, so that it has a layered structure. It was found that ion exchange was carried out while maintaining the above.
Analysis by ^{1 H} solid NMR samples A 'are set in reference to the measurement of sodium titanate hydrate was performed using things dry state at 110 ° C.. In sample A', as shown in FIG. 11, five peaks of 12.1 ppm, 10.2 ppm, 7.8 ppm, 5.3 ppm, and 1.63 ppm (derived from the measuring container) were confirmed by peak separation.

(Manufacturing method of new titanium oxide)
Approximately 0.5 g of Sample A'was placed in an alumina container, fired in air at 260 ° C. for 5 hours using a box-type electric furnace, and then cooled in the furnace to obtain Sample A'.

Comparative Example 1
HTO (Sample B) was obtained by the method of Patent Document 2.

(Analysis of new titanium oxide [Sample A]] and HTO [Sample B])
The sample A "obtained in this way was found to contain Ti and O as constituent elements by elemental analysis by characteristic X-ray measurement using an energy dispersive X-ray spectroscope (FIG. 12). In addition, FIG. 13 shows the absorption spectrum measurement of sample A ”and sample B by FT-IR. A broad absorption peak was observed near 3300 cm ^-1 (arrow in FIG. 13) in sample A ", and an absorption peak was observed near 3420 cm ^-1 in sample B. From this, OH groups were observed in sample A" and sample B. It turned out to exist. Further 500~1000cm around ^-1 is an area stretching vibration by Ti-O-Ti skeleton appears, the absorption spectrum by stretching vibration of Ti-O-Ti skeleton 760 cm ^-1 and 960 cm ^-1 in the sample A " in seen. sample B but absorption spectrum was observed at 760 cm ^-1 and 910 cm ^-1, the position of the peak of the high-wavenumber side is different from the sample a ".
According to the thermogravimetric analysis of FIG. 14, in sample A ", weight loss and endothermic reaction due to heating from room temperature to around 200 ° C. were observed, and desorption of adsorbed water and water incorporated in layers and crystal structures occurred. The weight loss when heated to 600 ° C. where there was almost no change in weight was 4.04 wt%. In addition, sample A "9.25 mg immediately after heating at 260 ° C. and dehydrated. When the sample was left in the air for 3 days, an increase in weight of 0.54 mg (5.8 wt%) was confirmed, and it was found that a structure such as a layered structure that easily absorbs water in the air remains. The thermogravimetric analysis of sample B showed that almost no weight loss occurred when heated to around 200 ° C., and that there was almost no adsorbed water or water taken in between layers. Further, the weight loss of sample B when heated to 600 ° C. was 2.19 wt%, which was significantly different from that of sample A ”when heated.
Sample A ”shows a pattern as shown in FIG. 15 by powder X-ray diffraction using CuKα as a radiation source, and 2θ = 14.0 °, 24.4 °, 28.8 °, 44.0 °, It had at least peaks at 48.1 °, 57.3 °, and 67.1 °, and the peak was widespread as a whole. The peak half width at 2θ = 24.4 ° and 48.1 ° was It was 1.18 ° and 0.34 °, respectively. Sample B was 2θ = 14.0 °, 24.7 °, 28.7 °, 44.4 °, 48.5 °, 57.5 °, respectively. , 67.1 °, and the peak widths at 2θ = 24.7 ° and 48.5 ° were 0.19 ° and 0.20 °, respectively.
Sample A "analysis by ^{1 H} solid NMR the sample B are set in reference to the measurement of sodium titanate hydrate was performed using things dry state at 110 ° C.. Sample A in FIG. 16" and the sample the ^{1 H} solid NMR measurement results of B, showed a peak position and peak intensity ratio after peak separation in Table 4. In "Sample A", signal peaks were shown at peak 1 (10.22 ppm, derived from the sample), peak 2 (7.15 ppm, derived from the sample), and peak 3 (1.63 ppm, derived from the measuring container) by peak separation. analysis by ¹ H solid NMR sample B, and with the signal peaks in 10.01Ppm (peak 1) and 6.62Ppm (peak 2) was different from the sample a ". The peak intensity ratio (I _{peak 1} / I _{peak 2} ) of sample A "was 0.47 and was 2.74 in sample B. From these facts, the peaks in sample A" and sample B It was revealed that the positions and peak intensity ratios are different, that is, the local structure of H and its abundance ratio are different, and the substances are different.

(Lithium secondary battery)
Using the sample A "and sample B thus obtained as active materials, acetylene black as a conductive agent and polytetrafluoroethylene as a binder are blended in a weight ratio of 5: 5: 1 to prepare an electrode. A 1M solution prepared by dissolving lithium hexafluorophosphate in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and diethyl carbonate (DEC) using lithium metal as the counter electrode was used as the electrolytic solution. A lithium secondary battery (coin-type cell) having the structure shown in FIG. 17 was prepared, and the electrochemical lithium insertion / removal behavior was measured. The battery was manufactured according to a known cell structure / assembly method. It was.

The produced lithium secondary battery was electrochemically subjected to a lithium insertion / desorption test at a current density of 10 mA / g and a cutoff potential of 3.0 V-1.0 V under a temperature condition of 25 ° C. When lithium was inserted, the voltage reached 1.0 V and then maintained 1.0 V for 2 hours. FIG. 18 shows the voltage change due to the insertion / removal of lithium. It was found that all of them have a flat voltage portion near 1.6 V and can perform a reversible lithium insertion / desorption reaction. When the lithium insertion amount of "Sample A" was evaluated when the voltage reached 1.0 V, the initial insertion amount per active material weight was 286 mAh / g, which was higher than that of Sample B of 259 mAh / g. The initial desorption amount of "Sample A" was 247 mAh / g, and the initial charge / discharge efficiency was 86%, which was almost the same as that of Sample B (86%). Furthermore, it was clarified that the sample A "can maintain a discharge capacity of 246 mAh / g even after 10 cycles. From the above, the novel titanium oxide active material of the present invention is more reversible than the sample B. It has been clarified that a high lithium insertion / removal reaction is possible and it is promising as a lithium secondary battery electrode material.

Example 2
In the synthesis of sodium titanate hydrate of Example 1, 20 mg of conductive carbon fine particles (Super C65 manufactured by TIMICAL, specific surface area 46 m ² / g) were added and synthesized to obtain Sample C.
As shown in FIG. 19 and Table 2, Sample C was subjected to powder X-ray diffraction using CuKα as a radiation source to obtain 2θ = 10.37 °, 15.73 °, 24.9 °, 29.7 °, 48. It has at least a peak at 52 °, and the peak half widths of the peaks existing at 2θ = 24.9 °, 29.7 °, and 48.52 ° are 0.29 °, 0.49 °, and 0. It was 29 °.
Sample C, which was ion-exchanged and fired in the same manner as in Example 1 (Sample C "), showed the same powder X-ray diffraction pattern as in Example 1 (FIG. 15) (FIG. 20), and 2θ = The peak half widths of 24.4 ° and 48.2 ° were 1.0 ° and 0.45 °, respectively.
A lithium secondary battery was prepared using Sample C ”in the same manner as in Example 1, and the electrochemical lithium insertion / removal was measured. As a result, the initial insertion amount, initial removal amount, and initial charge per active material weight were measured. The discharge efficiencies were 288 mAh / g, 250 mAh / g, and 87%, respectively.

Comparative Example 2
In the synthesis of sodium titanate hydrate of Example 1, the synthesis was carried out at a hydrothermal synthesis temperature of 180 ° C. to obtain Sample D.
As shown in FIG. 21 and Table 2, Sample D peaked at least at 2θ = 9.8 °, 24.1 °, 28.3 °, and 48.1 ° by powder X-ray diffraction using CuKα as a radiation source. The peak half widths of the peaks existing at 2θ = 24.1 °, 28.3 °, and 48.1 ° were 1.38 °, 1.92 °, and 0.84 °, respectively. ..
Sample D'obtained by ion-exchanged Sample D in the same manner as in Example 1 has a low crystallinity of the precursor sodium titanate hydrate, so that the crystal structure collapses during the ion exchange process, and the sample is a sample. The powder X-ray diffraction pattern was different from that of A'(FIG. 10) (FIG. 22). Further, Sample D'obtained by calcining Sample D'in the same manner as in Example 1 was a titanium oxide containing anatase as a main component, which was different from Example 1 (FIG. 15).

Comparative Example 3
In the synthesis of sodium titanate hydrate of Example 1, the synthesis was carried out with the hydrothermal synthesis time set to 6 hours to obtain Sample E.
As shown in FIG. 23 and Table 2, sample E peaked at least at 2θ = 9.3 °, 24.0 °, 28.1 °, and 48.2 ° by powder X-ray diffraction using CuKα as a radiation source. The peak half widths of the peaks existing at 2θ = 24.0 °, 28.1 °, and 48.2 ° were 0.80 °, 1.71 °, and 0.63 °, respectively. ..

Comparative Example 4
In the synthesis of sodium titanate hydrate of Example 1, the synthesis was carried out with 15 g of NaOH (7.5 times the weight ratio of TiO ₂ ) to obtain Sample F.
As shown in FIG. 24 and Table 2, sample F peaked at least at 2θ = 8.8 °, 24.1 °, 28.2 °, and 48.1 ° by powder X-ray diffraction using CuKα as a radiation source. The peak half widths of the peaks existing at 2θ = 24.1 °, 28.2 °, and 48.1 ° were 1.11 °, 1.53 °, and 0.86 °, respectively. ..

Example 3
In the synthesis of sodium titanate hydrate of Example 1, 3.55 g of sodium sulfate was added and the synthesis was carried out to obtain Sample G.
As shown in FIG. 25 and Table 2, the sample G was subjected to powder X-ray diffraction using CuKα as a radiation source, and 2θ = 10.29 °, 15.63 °, 24.92 °, 29.66 °, 48. It has at least a peak at 41 °, and the peak half widths of the peaks existing at 2θ = 24.92 °, 29.66 °, and 48.41 ° are 0.17 °, 0.29 °, and 0. It was 23 °.

Example 4
Sample A'of Example 1 was calcined in air at 300 ° C. for 5 hours and then cooled in a furnace to obtain Sample A "-2.
Sample A "-2 shows a pattern as shown in FIG. 26 by powder X-ray diffraction using CuKα as a radiation source, and the peak half widths of 2θ = 24.6 ° and 48.3 ° are 1. It was 18 ° and 0.45 °.
A lithium secondary battery was prepared using Sample A "-2 in the same manner as in Example 1, and the electrochemical lithium insertion / removal was measured. As a result, the initial insertion amount, the initial removal amount, and the initial removal amount per the weight of the active material were measured. The initial charge / discharge efficiencies were 274 mAh / g, 248 mAh / g, and 91%, respectively.

Example 5
Sample A'of Example 1 was calcined in air at 400 ° C. for 5 hours and then cooled in a furnace to obtain Sample A "-3.
Sample A "-3 shows a pattern as shown in FIG. 27 by powder X-ray diffraction using CuKα as a radiation source, and the peak half widths of 2θ = 24.8 ° and 48.3 ° are 0. It was 9 ° and 0.5 °.
A lithium secondary battery was prepared using Sample A "-3 in the same manner as in Example 1, and the electrochemical lithium insertion / removal was measured. As a result, the initial insertion amount, the initial removal amount, and the initial removal amount per the weight of the active material were measured. The initial charge / discharge efficiencies were 262 mAh / g, 248 mAh / g, and 95%, respectively.

Example 6
In the synthesis of sodium titanate hydrate of Example 1, 50 ml (solid content content 21.5 mg) of graphene oxide suspension (manufactured by Graphene Supermarket) was used instead of distilled water to obtain sample H. It was.
As shown in FIG. 28 and Table 2, the sample H was subjected to powder X-ray diffraction using CuKα as a radiation source, and 2θ = 10.43 °, 15.68 °, 25.0 °, 29.76 °, 48. It has at least a peak at 53 °, and the peak half widths of the peaks existing at 2θ = 25.0 °, 29.81 °, and 48.53 ° are 0.19 °, 0.43 °, and 0. It was 29 °.
Sample H, which was ion-exchanged and fired in the same manner as in Example 1 (Sample H "), showed the same powder X-ray diffraction pattern as in Example 1 (FIG. 15) (FIG. 29), and 2θ = The peak half-value widths of 24.45 ° and 48.17 ° were 1.1 ° and 0.33 °, respectively.
A lithium secondary battery was prepared using Sample H ”in the same manner as in Example 1, and the electrochemical lithium insertion / desorption was measured. As a result, the initial insertion amount, initial desorption amount, and initial charge per active material weight were measured. The discharge efficiencies were 292 mAh / g, 249 mAh / g, and 85%, respectively.

Example 7
In the synthesis of sodium titanate hydrate of Example 1, synthesis was carried out using titania hydrate containing about 1 wt% of conductive carbon fine particles (Super C65 manufactured by TIMICAL, specific surface area 46 m ² / g) as a titanium source. This was performed to obtain sample I. The titania hydrate containing conductive carbon fine particles is prepared by suspending the conductive carbon fine particles in an aqueous solution in which titanyl sulfate and urea are dissolved and heating in a water bath to precipitate the titania hydrate while containing the conductive carbon fine particles. Obtained by generating.
As shown in FIG. 30 and Table 2, Sample I was subjected to powder X-ray diffraction using CuKα as a radiation source to obtain 2θ = 10.3 °, 15.73 °, 24.97 °, 29.7 °, 48. It has at least a peak at 48 °, and the peak half widths of the peaks existing at 2θ = 24.97 °, 29.7 °, and 48.48 ° are 0.14 °, 0.36 °, and 0. It was 24 °.
Sample I which was ion-exchanged and fired in the same manner as in Example 1 (Sample I ”) showed the same powder X-ray diffraction pattern as in Example 1 (FIG. 15) (FIG. 31), and 2θ = The peak half-value widths of 24.55 ° and 48.2 ° were 1.22 ° and 0.36 °, respectively.
A lithium secondary battery was prepared using Sample I ”in the same manner as in Example 1, and the electrochemical lithium insertion / desorption was measured. As a result, the initial insertion amount, initial desorption amount, and initial charge per active material weight were measured. The discharge efficiencies were 283 mAh / g, 249 mAh / g, and 88%, respectively.

According to the present invention, it is possible to produce a novel titanium oxide containing H having a characteristic local structure and having a characteristic vibration of the Ti-O-Ti skeleton. Since this method does not require special equipment and the raw materials used are low in price, it is possible to produce high value-added materials at low cost.
In particular, the novel titanium oxide obtained by the method of the present invention has an extremely high practical value as a lithium secondary battery electrode material having a high capacity and excellent initial charge / discharge efficiency and cycle characteristics. ..

In addition, a lithium secondary battery that uses this titanium oxide as an active material as an electrode material is expected to have a high capacity, is capable of reversible lithium insertion / desorption reactions, and is capable of supporting long-term charge / discharge cycles. Is.

1: Coin-type lithium secondary battery
2: Negative electrode terminal
3: Negative electrode
4: Separator + electrolyte
5.: Insulation packing
6: Positive electrode
7: Positive electrode can

Claims (8)

Contains H,
^{In 1} H solid-state NMR measurement, the peak tops of 9-11 ppm (peak 1) and 6.7-8 ppm (peak 1) when the spectrum obtained from a sample at room temperature rotated at 1000 to 12,500 rpm using an electromagnetic wave of 400 MHz were peak-separated. It exists in peak 2), and the peak intensity ratio (I _{peak 1} / I _{peak 2} ) of these _{two peaks} is 1.0 or less.
Titanium oxide. The titanium oxide has an absorption peak at 930 to 990 cm ^-1 in infrared absorption analysis.
The titanium oxide according to claim 1. In the powder X-ray diffraction pattern of the titanium oxide as a radiation source of CuKα, the peak half widths of the peaks existing at 2θ = 24.2 to 25.2 ° and 47.9 to 48.6 ° are 0, respectively. .5-2 ° and 0.25-1 °,
The titanium oxide according to claim 1 or 2. The method for producing a titanium oxide according to any one of claims 1 to 3.
A step of synthesizing sodium titanate hydrate by a hydrothermal synthesis method using a solution in which a titanium source and a sodium source are dissolved or suspended, and
The step of synthesizing the proton exchanger of the sodium titanate hydrate, and
A step of heat-treating the proton exchanger of the sodium titanate hydrate in an oxygen gas-containing atmosphere or an inert gas atmosphere, and
A method for producing a titanium oxide having. The sodium titanate hydrate has 2θ = 10.1 to 10.5 °, 15.4 to 15.8 °, and 24.7 to 25.1 ° in a powder X-ray diffraction pattern using CuKα as a radiation source. , 29.4 to 29.8 °, 48.2 to 48.6 °, with at least peaks at 2θ = 24.7 to 25.1 °, 29.4 to 29.8 °, 48. The peak half-value widths of the peaks existing at 2 to 48.6 ° are 0.8 ° or less, respectively.
The method for producing a titanium oxide according to claim 4. When the sodium titanate hydrate peak-separated the spectrum obtained from a room temperature sample rotated at 1000 to 12500 rpm using an electromagnetic wave of 400 MHz in ¹ H solid-state NMR measurement, the peak top was 11.4 to 11.4 to Present at 12.7 ppm and 6.4-7.6 ppm,
The method for producing a titanium oxide according to claim 4 or 5. An electrode active material containing the titanium oxide according to any one of claims 1 to 3. A power storage device using the electrode active material according to claim 7.