JP5196486B2 - Method for producing composite titanium oxide - Google Patents

Description

  The present invention relates to a method for producing a composite titanium oxide.

  Currently, in Japan, lithium primary batteries are used as power sources for cameras and watches, and lithium secondary batteries are used as portable electronic devices such as mobile phones and laptop computers. Lithium batteries are one of the important storage batteries. It has become. In addition, lithium secondary batteries are expected to be put into practical use as large batteries such as hybrid cars and power load leveling systems in the future, and their importance is increasing.

  This lithium battery has a positive electrode and a negative electrode each containing a material capable of inserting and extracting lithium, and a separator or a solid electrolyte containing a non-aqueous electrolyte as main components.

Among these constituent elements, manganese dioxide (MnO ₂ ), lithium cobalt oxide (LiCoO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium titanium oxide are considered as active materials for electrodes. Examples thereof include oxides such as products (Li ₄ Ti ₅ O ₁₂ ), metals such as lithium metal, lithium alloy and tin alloy, and carbon materials such as graphite and MCMB (mesocarbon microbeads).

  Regarding these materials, the voltage of the battery is determined by the difference in chemical potential in the lithium content in each active material, but it is a feature of the lithium battery that a large potential difference can be formed particularly by combination.

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

  In the future, chemical batteries such as lithium batteries and capacitors are expected to be large, long-life, such as automotive power supplies, large-capacity backup power supplies, and emergency power supplies. There has been a need for a higher performance (high capacity) electrode active material in combination with a material active material.

  Of these, titanium oxide active materials have a voltage of about 1 to 2 V when lithium metal is used for the counter electrode, so the possibility of materials having various crystal structures as electrode active materials is examined. Has been.

In particular, an electrode including a spinel-type lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ) active material has a potential flat portion of about 1.5 V with respect to lithium, and a high capacity of about 175 mAh / g is obtained. Therefore, it is attracting attention and is mainly used for lithium secondary batteries.

  In addition, since a theoretical capacity exceeding 300 mAh / g is expected, various composite titanium oxides mainly composed of titanium dioxide have been studied as electrode materials.

Among these, H ₂ Ti ₆ O ₁₃ has a Na ₂ Ti ₆ O ₁₃ type tunnel structure crystal structure, is capable of lithium insertion, and has a stable skeletal structure, so that high capacity is expected. It was.

The crystal structure of the Na ₂ Ti ₆ O ₁₃ type tunnel structure of this compound is characterized by having a tunnel space in which two hydrogens can be occupied by a unit in which three TiO ₆ octahedrons are connected. The skeleton structure is shown in FIG. In FIG. 1, an octahedron represents a TiO ₆ octahedron, and titanium is occupied in the center thereof.

As a method for producing this compound, a method for proton exchange of sodium of sodium titanium oxide Na ₂ Ti ₆ O ₁₃ has been known so far, but in this method, most of the sodium remains without being exchanged, The resulting chemical composition is reported to be Na _1.98 H _0.02 Ti ₆ O ₁₃ . (Non-Patent Document 1)

On the other hand, a layered structure sodium titanium oxide Na ₂ Ti ₃ O ₇ proton exchanger H ₂ Ti ₃ O ₇ having a similar chemical composition is used as a starting material, and a dehydration reaction described by the following formula is used to make H ₂ Ti. A method for producing ₆ O ₁₃ has been reported. (See Non-Patent Document 2 and Patent Document 1)

2H ₂ Ti ₃ O ₇ → H ₂ Ti ₆ O ₁₃ + H ₂ O

  However, it is difficult to strictly control the dehydration reaction, and in this method, an impurity phase is always observed in the product. (Non-Patent Document 2)

  A sample in which such an impurity phase is mixed is studied as an electrode material, and a high insertion capacity of about 283 mAh / g is reported in Patent Document 1.

From this, it was expected that a high capacity exceeding 300 mAh / g could be realized by using H ₂ Ti ₆ O ₁₃ containing almost no impurities as an electrode material.

However, it has been difficult to synthesize single-phase H ₂ Ti ₆ O ₁₃ by known production processes.
Japanese Patent Application No. 2008-039820 S. Papp, L.M. Korosl, V.M. Meyen, P.M. Cool, E .; F. Vansant, I.D. Decany, Journal of Solid State Chemistry, 178, 1614-1619 (2005) T.A. P. Feist, P.M. K. Davids, Journal of Solid State Chemistry, 101, 275-295 (1992)

The present invention solves the above-described problems and provides a production method capable of obtaining a single phase of composite titanium oxide H ₂ Ti ₆ O ₁₃ that is important as a lithium battery electrode material that can be expected to have a high capacity. There is to do.

As a result of diligent study, the present inventor has produced a lithium exchanger Li ₂ Ti ₆ O _{13 in} which sodium ₂ is first exchanged for lithium, using Na ₂ Ti ₆ O ₁₃ as a starting material, as a method for producing H ₂ Ti ₆ O _13. Furthermore, a manufacturing method for exchanging the lithium with protons is clarified, and the obtained product is a single phase of H ₂ Ti ₆ O ₁₃ , and a lithium battery including an electrode containing the active material as a constituent member The present invention was completed by producing and confirming a high insertion capacity as compared with known H ₂ Ti ₆ O ₁₃ .

That is, the present invention provides a method for producing a composite titanium oxide _H 2 _Ti 6 _{O 13} shown below.
(1) The chemical formula H ₂ Ti ₆ includes a step of proton exchange using Li ₂ Ti ₆ O ₁₃ synthesized by the step of ion exchange of sodium titanium oxide Na ₂ Ti ₆ O ₁₃ as a starting material. method for producing a composite titanium oxide represented by O _13.
(2) The method for producing a composite titanium oxide according to (1), wherein the crystal structure of the composite titanium oxide is a monoclinic Na ₂ Ti ₆ O ₁₃ type tunnel structure.
(3) The monoclinic lattice constant of the composite titanium oxide is determined by the amount of residual sodium and lithium, the a-axis length is 1.46 to 1.48 nm, and the b-axis length is 0.373 to 0.003. 375 nm, method of producing a composite titanium oxide according to the c-axis length 0.91~0.93nm, β corners, characterized in that in the range of 96~99 ° (1).
(4) The step of ion-exchanging the sodium titanium oxide Na ₂ Ti ₆ O ₁₃ applies a lithium ion exchange reaction using a lithium molten salt, The production of a composite titanium oxide according to (1) Method.
(5) The method for producing a composite titanium oxide according to (4), wherein the heat treatment temperature in the lithium ion exchange reaction using the lithium molten salt is in the range of 30 ° C. to 500 ° C.
(6) The method for producing a composite titanium oxide according to (1), wherein the proton exchange step uses a proton exchange reaction using an acidic aqueous solution.
(7) The method for producing a composite titanium oxide according to (6), wherein the heat treatment temperature in the proton exchange reaction using the acidic aqueous solution is in the range of 20 ° C to 100 ° C.

According to the present invention, a single phase of composite titanium oxide H ₂ Ti ₆ O ₁₃ can be produced, and a high-capacity lithium battery can be obtained by using this compound as an active material for an electrode material.

The production method of the present invention is a production process in which a single phase of composite titanium oxide H ₂ Ti ₆ O ₁₃ that can be used as a lithium battery electrode active material can be produced. Sodium titanium oxide Na ₂ Ti ₆ O ₁₃ is ionized. The method is characterized by a proton exchange step using Li ₂ Ti ₆ O ₁₃ synthesized in the exchange step as a starting material.
Further, in the production process of the present invention, a lithium ion exchange reaction using a lithium molten salt is applied as an ion exchange method.
Furthermore, in the production process of the present invention, a proton exchange reaction using an acidic aqueous solution is applied as a proton exchange method.

  The production method according to the present invention will be described in more detail.

(Method for producing starting material Na ₂ Ti ₆ O ₁₃ )
Of the present invention, the Na ₂ Ti ₆ O ₁₃ polycrystal as a starting material has a chemical composition of Na ₂ Ti ₆ O ₁₃ with at least one sodium compound and at least one titanium compound as raw materials. Thus, it can be manufactured by weighing and mixing, and heating in an atmosphere containing oxygen gas such as air.

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 NaNO ₃ , hydroxides such as NaOH, etc. Is mentioned. Among these, Na ₂ CO ₃ is particularly preferable.

As the titanium raw material, at least one of titanium (metallic titanium) and a titanium compound is used. The titanium compound is not particularly limited as long as it contains titanium, and examples thereof include oxides such as TiO, Ti ₂ O ₃ and TiO ₂ , salts such as TiCl _{4 and the} like. Among these, TiO ₂ is particularly preferable.

First, a mixture containing these is prepared. The mixing ratio of sodium raw material and titanium material _is preferably mixed such that the chemical composition of Na ₂ Ti _{6 O 13.} In addition, since sodium easily volatilizes during heating, the amount of sodium should be slightly more excessive than 2 in the above chemical formula, and preferably in the range of 2.0 to 2.1. Moreover, a mixing method is not specifically limited as long as these can be mixed uniformly, For example, what is necessary is just to mix by a wet type or a dry type using well-known mixers, such as a mixer.

  The mixture is then fired. The firing temperature can be appropriately set depending on the raw material, but is usually about 600 ° C to 1200 ° C, preferably 700 ° C to 1050 ° C. Also, the firing atmosphere is not particularly limited, and it is usually performed in an oxidizing atmosphere or air. The firing time can be appropriately changed according to the firing temperature and the like. The cooling method is not particularly limited, but may be natural cooling (cooling in the furnace) or slow cooling.

  After firing, the fired product may be pulverized by a known method as necessary, and the above firing step may be further performed. That is, in the method of the present invention, it is preferable that the mixture is repeatedly fired, cooled and pulverized twice or more. Note that the degree of pulverization may be adjusted as appropriate according to the firing temperature and the like.

(Method for producing lithium exchanger Li ₂ Ti ₆ O ₁₃ )
Next, using Na ₂ Ti ₆ O ₁₃ obtained as described above as a starting material, by applying a lithium ion exchange reaction in a molten salt containing a lithium compound, almost all of the sodium in the starting material compound was exchanged for lithium. A lithium ion exchanger active material Li ₂ Ti ₆ O ₁₃ is obtained.

In this case, it is preferable to perform the ion exchange treatment while dispersing the pulverized Na ₂ Ti ₆ O ₁₃ in the molten salt containing the lithium compound. As the molten salt, a molten salt containing any one or more of salts that melt at a relatively low temperature such as lithium nitrate, lithium chloride, lithium bromide, and lithium iodide can be used. As a preferred method, a lithium salt is melted in advance, and Na ₂ Ti ₆ O ₁₃ powder is added thereto. The mixing ratio is usually 3 to 100, preferably 10 to 30, as a ratio of the weight of the entire lithium salt to the weight of Na ₂ Ti ₆ O ₁₃ .

  The temperature of the ion exchange treatment is in the range of 30 ° C to 500 ° C, preferably 200 ° C to 400 ° C. The treatment time is usually 2 to 72 hours, preferably 5 to 50 hours.

Furthermore, as a method of the lithium ion exchange treatment, a method of treating in an organic solvent or an aqueous solution in which a lithium compound is melted is also suitable. In this case, the pulverized Na ₂ Ti ₆ O ₁₃ raw material is put into an organic solvent or water in which a lithium compound is dissolved at a constant concentration, and the mixture is treated at a temperature not higher than the boiling point of the organic solvent or water. In order to avoid evaporation of the solvent, it is preferable to perform ion exchange while refluxing the solvent. The treatment temperature is usually 30 ° C to 300 ° C, preferably 50 ° C to 180 ° C. The treatment time is not particularly limited, but is usually 5 to 50 hours, preferably 10 to 20 hours.

  As the lithium compound used in the present invention, hydroxide, carbonate, acetate, nitrate, oxalate, halide, butyllithium and the like are preferable, and these are used alone or in combination of two or more as required. . As the organic solvent used in the present invention, higher alcohols such as hexanol and ethoxyethanol, ethers such as diethyl glycol monoethyl ether, or organic solvents having a boiling point of 140 ° C. or more have good workability. This is preferable. These may be used alone or in combination of two or more as required.

The density | concentration of the lithium compound in an organic solvent or aqueous solution is 3-10 mol% normally, Preferably it is 5-8 mol%. Further, the dispersion concentration of the Na ₂ Ti ₆ O ₁₃ raw material in the organic solvent or the aqueous solution is not particularly limited, but is preferably about 1 to 20% by weight from the viewpoint of operability and economy.

After the ion exchange treatment, the obtained product is washed with ethanol or the like and then dried to obtain a target lithium ion exchanger represented by the chemical formula Li ₂ Ti ₆ O ₁₃ . The washing method and the drying method are not particularly limited, and a normal method may be used, or natural drying in a desiccator or the like may be used.

The Li ₂ Ti ₆ O ₁₃ obtained in this way is obtained by changing the conditions for the exchange treatment so that the amount of sodium remaining from the starting material is changed from the chemical composition leaving a significant amount by the wet method. It is possible to control the chemical composition below the detection limit of chemical analysis.

(Production method of proton exchanger H ₂ Ti ₆ O ₁₃ )
Then, as the starting material the Li ₂ Ti ₆ O ₁₃ obtained by the above, by applying the proton exchange reaction in an acidic aqueous solution, the proton exchange nearly all of the lithium in the starting material compound is replaced with hydrogen body H ₂ Ti ₆ O ₁₃ is obtained.

In this case, it is preferable to disperse the pulverized Li ₂ Ti ₃ O ₇ in an acidic solution, hold it for a certain time, and then dry it. As the acid to be used, an aqueous solution containing any one or more of hydrochloric acid, sulfuric acid, nitric acid and the like having any concentration is suitable. Of these, use of dilute hydrochloric acid having a concentration of 0.1 to 1.0 N is preferable. The treatment time is 10 hours to 10 days, preferably 1 day to 7 days. In order to shorten the processing time, it is preferable to replace the solution with a new one as appropriate. Furthermore, in order to facilitate the exchange reaction, the treatment temperature is preferably higher than room temperature and 30 ° C. to 100 ° C. A known drying method can be applied to the drying, but vacuum drying or the like is more preferable.

The H ₂ Ti ₆ O ₁₃ obtained in this way is optimized for the conditions of the exchange treatment, so that the amount of sodium and lithium remaining from the starting material can be detected by the detection limit of chemical analysis by a wet method. It is possible to reduce to the following.

  Hereinafter, examples will be shown to further clarify the features of the present invention. The present invention is not limited to these examples.

[Example 1]
(Method for producing starting material Na ₂ Ti ₆ O ₁₃ )
Sodium carbonate (Na ₂ CO ₃ ) powder with a purity of 99% or more and titanium dioxide (TiO ₂ ) powder with a purity of 99.99% or more were weighed so that the molar ratio was Na: Ti = 2.02: 6. After mixing these in a mortar, they were filled in a JIS standard platinum crucible and heated in an air at high temperature using an electric furnace. The firing temperature was 800 ° C. and the firing time was 20 hours. Then, after naturally cooling in an electric furnace, it was again pulverized and mixed in a mortar and refired at 800 ° C. for 20 hours to obtain a Na ₂ Ti ₆ O ₁₃ polycrystal as a starting material.

When the chemical composition of the obtained sample was analyzed by ICP emission analysis, Na: Ti = 2.0: 6 (analysis error of each element: within 0.04), and the chemical formula of Na ₂ Ti ₆ O ₁₃ It was reasonable. Furthermore, it was revealed by an X-ray powder diffractometer that the crystal has a monoclinic system and a single phase having a crystal structure of space group C2 / m having good crystallinity. The powder X-ray diffraction pattern of Na ₂ Ti ₆ O ₁₃ is shown in FIG. Further, when the lattice constant was determined by the least square method using each index and its surface spacing, the following values were obtained, which were in good agreement with the known Na ₂ Ti ₆ O ₁₃ value.
a = 1.5072 nm (error: within 0.0005 nm)
b = 0.3738 nm (error: within 0.0001 nm)
c = 0.9154 nm (error: within 0.0003 nm)
β = 99.00 ° (error: within 0.02 °)

When the particle shape of the Na ₂ Ti ₆ O ₁₃ polycrystal thus obtained was examined by a scanning electron microscope (SEM), the polycrystal was a primary having an isotropic shape of about 1 micron square. It was revealed that it was composed of particles.

(Method for producing ion exchanger Li ₂ Ti ₆ O ₁₃ )
Using the pulverized product of Na ₂ Ti ₆ O ₁₃ synthesized as described above as a starting material, anhydrous lithium nitrate (LiNO ₃ ) powder with a purity of 99% or more and Na ₂ Ti ₆ O ₁₃ : LiNO ₃ = by weight ratio = Weighed to be 1:20. These were mixed in a mortar, then filled in an alumina crucible, and held in air at 380 ° C. for 10 hours using an electric furnace to perform lithium ion exchange treatment. Thereafter, pure water, and it was washed well with ethanol, by air _drying, to obtain a Li ₂ Ti _{6 O 13.}

When the chemical composition of the obtained sample was analyzed by ICP emission spectrometry, Na: Li: Ti = 0.03: 1.97: 6 (analysis error of each element: within 0.04) It was clarified that the amount of sodium to be contained is less than the analysis error and has a composition that does not contain sodium. Furthermore, with an X-ray powder diffractometer, a single phase of Li ₂ Ti ₆ O ₁₃ having a monoclinic system, a space group C2 / m of a Na ₂ Ti ₆ O ₁₃ type tunnel structure having good crystallinity It became clear that there was. The powder X-ray diffraction pattern of Li ₂ Ti ₆ O ₁₃ is shown in FIG. Further, when the lattice constant was determined by the least square method using each index and its surface spacing, the following values were obtained, which were in good agreement with the values of known Li ₂ Ti ₆ O ₁₃ .
a = 1.5334 nm (error: within 0.0003 nm)
b = 0.3751 nm (error: within 0.0001 nm)
c = 0.9148 nm (error: within 0.0002 nm)
β = 99.44 ° (error: within 0.01 °)

When the particle shape of Li ₂ Ti ₆ O ₁₃ obtained in this way was examined with a scanning electron microscope (SEM), the polycrystalline body retained the shape of Na ₂ Ti ₆ O ₁₃ as a starting material, It was revealed that the particles were composed of primary particles having an isotropic shape of about 1 micron square.

(Production method of proton exchanger H ₂ Ti ₆ O ₁₃ )
The pulverized product of Li ₂ Ti ₆ O ₁₃ synthesized above was used as a starting material, immersed in a 0.5N hydrochloric acid solution, and kept at 70 ° C. for 5 days to perform proton exchange treatment. In order to increase the exchange processing speed, the solution was changed every 12 hours. Thereafter, it was washed with water and dried in air at 70 ° C. for 24 hours to obtain a target proton exchanger H ₂ Ti ₆ O ₁₃ .

When the chemical composition of the obtained sample was analyzed by ICP emission spectrometry, Na: Li: Ti = 0.03: 0.08: 6 (analysis error of each element: within 0.04), significant However, when the remaining amount of sodium and lithium is assumed to be protons, the chemical composition is H _1.89 Li _0.08 Na _0.03 Ti ₆ O ₁₃ , and almost H ₂ Ti. It was revealed that the composition can be synthesized with a composition close to ₆ O ₁₃ . Furthermore, with an X-ray powder diffractometer, a single phase of H ₂ Ti ₆ O ₁₃ having a monoclinic, space group C2 / m Na ₂ Ti ₆ O ₁₃ type tunnel structure with good crystallinity It became clear that there was. FIG. 4 shows a powder X-ray diffraction pattern of H ₂ Ti ₆ O ₁₃ . Further, when the lattice constant was determined by the least square method using each index and its surface spacing, the following values were obtained, which were in good agreement with the known values of H ₂ Ti ₆ O ₁₃ .
a = 1.4680 nm (error: within 0.0003 nm)
b = 0.3746 nm (error: within 0.0001 nm)
c = 0.9261 nm (error: within 0.0001 nm)
β = 96.97 ° (error: within 0.02 °)

When the particle shape of the H ₂ Ti ₆ O ₁₃ polycrystal obtained in this way was examined by a scanning electron microscope (SEM), the polycrystal was found to be Na ₂ Ti ₆ O ₁₃ as a starting material and its lithium. It was revealed that the shape of the ion exchanger Li ₂ Ti ₆ O ₁₃ was maintained and composed of primary particles having an isotropic shape of about 1 micron square.

Moreover, about the validity of a chemical composition, as a result of the thermal analysis (TGA), the weight reduction of 3.7 wt% was confirmed by the heating to 600 degreeC. This was explained by the following decomposition reaction (calculated value 3.6 wt%), and it was confirmed that the chemical composition of H ₂ Ti ₆ O ₁₃ was appropriate.
H ₂ Ti ₆ O ₁₃ → H ₂ O ↑ + 6TiO ₂

(Lithium battery)
The H ₂ Ti ₆ O ₁₃ thus obtained was used as an active material, acetylene black as a conductive agent, and tetrafluoroethylene as a binder were blended in a weight ratio of 10: 5: 1 to produce an electrode. Then, using lithium metal as a counter electrode, a 1M solution in which lithium hexafluorophosphate is dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1: 1) is used as an electrolytic solution. A button-type lithium battery having the structure shown in FIG. 5 was prepared, and its electrochemical lithium insertion / extraction behavior was measured. The battery was produced according to a known cell configuration / assembly method.

The fabricated lithium secondary battery was subjected to an electrochemical lithium insertion test at a current density of 10 mA / g and a cut-off potential of 1.0 V under a temperature condition of 25 ° C. It has been found that a high voltage capacity of 327 mAh / g is obtained with a voltage flat portion in the vicinity of 0.5 V. (FIG. 6) After that, when a lithium desorption / insertion test was performed at a cut-off potential of 3.0 to 1.0 V, a gentle voltage change was observed at a potential near 1.8 V after the second cycle. However, it has been found that reversible lithium insertion / extraction is possible at a capacity of about 150 to 155 mAh / g. From the above, the H ₂ Ti ₆ O ₁₃ produced by the production method of the present invention is synthesized in a single phase without impurities, so in the past, in lithium batteries using electrodes using this material as an active material, As compared with the report (283 mAh / g), it became clear that a higher capacity was obtained, and the characteristics of the production method of the present invention became clear.

[Example 2]
(Method for producing ion exchanger Li ₂ Ti ₆ O ₁₃ )
Using the pulverized Na ₂ Ti ₆ O ₁₃ polycrystal synthesized in Example 1 as a starting material, anhydrous lithium nitrate (LiNO ₃ ) powder having a purity of 99% or more and Na ₂ Ti ₆ O ₁₃ : LiNO in a weight ratio It measured so that it might become ₃ = 1: 20. These were mixed in a mortar, then filled in an alumina crucible, and held in air at 320 ° C. for 10 hours using an electric furnace to perform lithium ion exchange treatment. Thereafter, pure water, and it was washed well with ethanol, by air _drying, to obtain a Li ₂ Ti _{6 O 13} active material.

When the chemical composition of the obtained sample was analyzed by ICP emission analysis, it was Na: Li: Ti = 0.10: 1.90: 6 (analysis error of each element: within 0.04), significant The amount of residual sodium was confirmed, but when compared with Example 1, since the ion exchange treatment temperature was higher, the residual amount tended to decrease. Furthermore, with an X-ray powder diffractometer, a single phase of Li ₂ Ti ₆ O ₁₃ having a monoclinic system, a space group C2 / m of a Na ₂ Ti ₆ O ₁₃ type tunnel structure having good crystallinity It became clear that there was. FIG. 7 shows a powder X-ray diffraction pattern of Li ₂ Ti ₆ O ₁₃ . Further, when the lattice constant was determined by the least square method using each index and its surface spacing, the following values were obtained, which were in good agreement with the values of known Li ₂ Ti ₆ O ₁₃ .
a = 1.5324 nm (error: within 0.0004 nm)
b = 0.3750 nm (error: within 0.0001 nm)
c = 0.9146 nm (error: within 0.0002 nm)
β = 99.41 ° (error: within 0.01 °)

When the particle shape of Li ₂ Ti ₆ O ₁₃ obtained in this way was examined with a scanning electron microscope (SEM), the polycrystalline body retained the shape of Na ₂ Ti ₆ O ₁₃ as a starting material, It was revealed that the particles were composed of primary particles having an isotropic shape of about 1 micron square.

(Production method of proton exchanger H ₂ Ti ₆ O ₁₃ )
The pulverized product of Li ₂ Ti ₆ O ₁₃ synthesized above was used as a starting material, immersed in a 0.5N hydrochloric acid solution, and kept at 70 ° C. for 5 days to perform proton exchange treatment. In order to increase the exchange processing speed, the solution was changed every 12 hours. Thereafter, it was washed with water and dried in air at 70 ° C. for 24 hours to obtain a target proton exchanger H ₂ Ti ₆ O ₁₃ .

When the chemical composition of the obtained sample was analyzed by ICP emission spectrometry, Na: Li: Ti = 0.09: 0.11: 6 (analysis error of each element: within 0.04), significant Of residual sodium and lithium were identified. Compared to Example 1, it was revealed that the lower lithium ion exchange treatment temperature affects the increase in the amount of residual sodium. As a result, the chemical analysis formula was H _1.80 Li _0.11 Na _0.09 Ti ₆ O ₁₃ . On the other hand, with an X-ray powder diffractometer, a single phase of H ₂ Ti ₆ O ₁₃ having a monoclinic system and a space group C2 / m of Na ₂ Ti ₆ O ₁₃ type tunnel structure having a good crystallinity. It became clear that there was. The powder X-ray diffraction pattern is shown in FIG. Further, when the lattice constant was obtained by the least square method using each index and its surface spacing, the following values were obtained, and the a-axis length was slightly longer and the c-axis length was slightly shorter than in Example 1. From the above, it was clarified that the lattice constant was changed by the influence of residual sodium and lithium.
a = 1.4694 nm (error: within 0.0003 nm)
b = 0.3746 nm (error: within 0.0001 nm)
c = 0.9252 nm (error: within 0.0002 nm)
β = 97.05 ° (error: within 0.02 °)

(Lithium battery)
Using the thus obtained H ₂ Ti ₆ O ₁₃ as an active material, a lithium battery similar to that of Example 1 was produced, and the current density was 10 mA / g and the cutoff was 1.0 V under the temperature condition of 25 ° C. When an electrochemical lithium insertion test was conducted up to the potential, it was found that the initial insertion reaction had a voltage flat portion around a voltage of 1.5 V, and a high capacity of 315 mAh / g was obtained. (FIG. 9) After that, when a lithium desorption / insertion test was performed at a cutoff potential of 3.0 to 1.0 V, a gentle voltage change was observed at a potential near 1.8 V after the second cycle. However, it has been found that reversible lithium insertion / extraction is possible at a capacity of about 140-150 mAh / g. From the above, it has been clarified that when the treatment temperature for lithium ion exchange in the production process of the present invention is lower than 380 ° C., the amount of residual sodium and lithium increases, and the battery capacity also decreases.

[Comparative Example 1]
(Method for producing H ₂ Ti ₆ O ₁₃ )
Using the pulverized product of Na ₂ Ti ₆ O ₁₃ polycrystal synthesized in Example 1 as a starting material, it was immersed in a 0.5N hydrochloric acid solution as it was without being subjected to lithium ion exchange treatment. Proton exchange treatment was attempted by holding for one day. Direct proton exchange treatment was performed.

  When the chemical composition of the obtained sample was analyzed by ICP emission spectrometry, Na: Ti = 1.99: 6 (analysis error of each element: within 0.04), most of the sodium remained, It was revealed that the proton exchange reaction hardly progressed. This result is in good agreement with the report of Non-Patent Document 1.

In the manufacturing process from the present invention described above, the lithium ion exchange treatment, was found to be essential in order to obtain H ₂ Ti ₆ O ₁₃ as a final product.

[Comparative Example 2]
(Manufacturing method of _Na 2 _Ti 3 _{O 7)}
Sodium carbonate (Na ₂ CO ₃ ) powder with a purity of 99% or more and titanium dioxide (TiO ₂ ) powder with a purity of 99.99% or more were weighed so that the molar ratio was Na: Ti = 2: 3. After mixing these in a mortar, they were filled in a JIS standard platinum crucible and heated in an air at high temperature using an electric furnace. The firing temperature was 800 ° C. and the firing time was 20 hours. Then, after naturally cooling in an electric furnace, it was pulverized and mixed again in a mortar and refired at 800 ° C. for 20 hours to obtain Na ₂ Ti ₃ O ₇ as a starting material.

When the chemical composition of the obtained sample was analyzed by ICP emission analysis, Na: Ti = 2.01: 3.00 (analysis error of each element: within 0.04), and Na ₂ Ti ₃ O ₇ The chemical formula was reasonable. Further, it was revealed by an X-ray powder diffractometer that the crystal has a monoclinic system and a single phase having a crystal structure of the space group P2 ₁ / m having good crystallinity. Further, when the lattice constant was obtained by the least square method using each index and its surface spacing, the following value was obtained, which was in good agreement with the known Na ₂ Ti ₃ O ₇ value.
a = 0.9131 nm (error: within 0.0001 nm)
b = 0.3804 nm (error: within 0.0001 nm)
c = 0.8569 nm (error: within 0.0001 nm)
β = 101.60 ° (error: within 0.01 °)

(Method for producing H ₂ Ti ₃ O ₇ )
The pulverized product of Na ₂ Ti ₃ O ₇ synthesized as described above was used as a starting material, immersed in a 0.5N hydrochloric acid solution, and kept at 70 ° C. for 5 days to perform proton exchange treatment. . In order to increase the exchange processing speed, the solution was changed every 12 hours. Thereafter, it was washed with water and dried in air at 70 ° C. for 24 hours to obtain a proton exchanger H ₂ Ti ₃ O ₇ .

When the chemical composition of the obtained sample was analyzed by ICP emission spectrometry, sodium was not detected, and the chemical formula of H ₂ Ti ₃ O ₇ which was almost completely proton-exchanged was appropriate. Furthermore, it was revealed by an X-ray powder diffractometer that the crystal has a monoclinic system and a single phase of H ₂ Ti ₃ O ₇ having a crystal structure of the space group C2 / m having good crystallinity. Further, when the lattice constant was obtained by the least square method using each index and its surface spacing, the following value was obtained, which was in good agreement with the known value of H ₂ Ti ₃ O ₇ .
a = 1.61010 nm (error: within 0.0001 nm)
b = 0.3861 nm (error: within 0.0001 nm)
c = 0.9466 nm (error: within 0.0001 nm)
β = 101.45 ° (error: within 0.01 °)

When the particle shape of H ₂ Ti ₃ O ₇ obtained in this way was examined by a scanning electron microscope (SEM), the polycrystalline body retained the shape of Na ₂ Ti ₃ O ₇ as a starting material, It was revealed that the particles were composed of primary particles having an isotropic shape of about 1 micron square.

The obtained H ₂ Ti ₃ O ₇ was heat-treated at 140 ° C. for 48 hours in air to obtain H ₂ Ti ₆ O ₁₃ .

About the obtained sample, X-ray-diffraction data was measured with the X-ray powder diffractometer, and it was confirmed that the phase which can be explained by the monoclinic system and the structural model of the space group C2 / m is main. However, compared with H ₂ Ti ₆ O ₁₃ produced by the manufacturing method of the present invention produced in Examples 1 and 2, the peak width is wide, and there are peaks that cannot be identified including shoulder peaks around 2θ = 13 °. It became clear that there were many. The powder X-ray diffraction pattern at this time is shown in FIG. When the lattice constant was obtained by the least square method using each index of the identifiable peak and its surface spacing, the following values were obtained.
a = 1.4614 nm (error: within 0.0002 nm)
b = 0.3729 nm (error: within 0.0001 nm)
c = 0.9231 nm (error: within 0.0002 nm)
β = 97.04 ° (error: within 0.01 °)

(Lithium battery)
Using the thus obtained H ₂ Ti ₆ O ₁₃ as an active material, electrodes were produced in the same manner as in Examples 1 and 2, and lithium batteries similar to those in Examples 1 and 2 were produced. The lithium battery was subjected to an electrochemical lithium insertion test under the same conditions as in Example 1. As a result, the lithium battery had a flat voltage portion around 1.6 V and the lithium insertion capacity was 283 mAh / g. (FIG. 11) From this, in the manufacturing method using H ₂ Ti ₃ O ₇ as the starting material, it is clear that the amount of the composite titanium oxide contributing to the electrochemical reaction is small because the impurity phase exists. It was.

The manufacturing method of the composite titanium oxide H ₂ Ti ₆ O ₁₃ of the present invention is a manufacturing process capable of obtaining a high-quality single-phase sample, and lithium using an electrode containing the composite titanium oxide as an active material. Since the battery has a high capacity exceeding 300 mAh / g, it has a high practical value as a method for producing a lithium battery electrode material oxide.

  Also, the manufacturing method does not require a special apparatus, and the raw material to be used is low in price, so that a high value-added material can be manufactured at a low cost.

Is a schematic diagram showing an _Na 2 _Ti 6 _{O 13} type tunnel _{structure H} 2 _Ti 6 _{O 13} is produced having the production method of the present invention. ₂ is an X-ray powder diffraction pattern of Na ₂ Ti ₆ O ₁₃ which is the starting material of the present invention obtained in Example 1. FIG. _{2 is} an X-ray powder diffraction pattern of a lithium ion exchanger Li ₂ Ti ₆ O ₁₃ which is a starting material of the present invention obtained in Example 1 under the condition of an ion exchange treatment temperature of 380 ° C. FIG. _{2 is} an X-ray powder diffraction pattern of the proton exchanger H ₂ Ti ₆ O ₁₃ of the present invention obtained in Example 1. FIG. It is a schematic diagram which shows an example of a structure of a lithium battery. It is a diagram illustrating a voltage change due to the lithium insertion reaction cell using a proton exchange material H ₂ Ti ₆ O ₁₃ of the present invention obtained in Example 1 as an electrode. 2 is an X-ray powder diffraction pattern of a lithium ion exchanger Li ₂ Ti ₆ O ₁₃ which is a starting material of the present invention obtained in Example 2 under conditions of an ion exchange treatment temperature of 320 ° C. FIG. 3 is an X-ray powder diffraction pattern of the proton exchanger H ₂ Ti ₆ O ₁₃ of the present invention obtained in Example 2. FIG. It is a diagram illustrating a voltage change due to the lithium insertion reaction cell using a proton exchange material H ₂ Ti ₆ O ₁₃ of the present invention obtained in Example 2 as an electrode. 4 is an X-ray powder diffraction pattern of H ₂ Ti ₆ O ₁₃ produced using H ₂ Ti ₃ O ₇ as a starting material in Comparative Example 2. FIG. The _H 2 _Ti 3 _{O 7} in Comparative Example 2 is a diagram illustrating a voltage change due to the lithium insertion reaction of the battery using the _H 2 _Ti 6 _{O 13} which are produced as a starting material as an electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Button type lithium battery 2 Negative electrode terminal 3 Negative electrode 4 Separator + Electrolyte 5 Insulation packing 6 Positive electrode 7 Positive electrode can

Claims (7)

The chemical formula H ₂ Ti ₆ O ₁₃ includes a step of proton exchange using Li ₂ Ti ₆ O ₁₃ synthesized by the step of ion exchange of sodium titanium oxide Na ₂ Ti ₆ O ₁₃ as a starting material. The manufacturing method of the composite titanium oxide represented. The method for producing a composite titanium oxide according to claim 1, wherein the crystal structure of the composite titanium oxide is a monoclinic Na ₂ Ti ₆ O ₁₃ type tunnel structure. The monoclinic lattice constant of the composite titanium oxide is determined by the amount of residual sodium and lithium, the a-axis length is 1.46 to 1.48 nm, the b-axis length is 0.373 to 0.375 nm, c 2. The method for producing a composite titanium oxide according to claim 1, wherein the axial length is 0.91 to 0.93 nm and the β angle is in the range of 96 to 99 °. 2. The method for producing a composite titanium oxide according to claim 1, wherein the step of ion exchange of the sodium titanium oxide Na ₂ Ti ₆ O ₁₃ applies a lithium ion exchange reaction using a lithium molten salt. The method for producing a composite titanium oxide according to claim 4, wherein a heat treatment temperature in the lithium ion exchange reaction using the lithium molten salt is in a range of 30 ° C to 500 ° C. The method for producing a composite titanium oxide according to claim 1, wherein the proton exchange step uses a proton exchange reaction using an acidic aqueous solution. The method for producing a composite titanium oxide according to claim 6, wherein the heat treatment temperature in the proton exchange reaction using the acidic aqueous solution is in the range of 20 ° C to 100 ° C.