WO2004059763A2

WO2004059763A2 - Titanium (iv) oxide material used as electrode material in batteries

Info

Publication number: WO2004059763A2
Application number: PCT/EP2003/014608
Authority: WO
Inventors: Volker Lorenzen; Elmar Hecht; Jörg PESCHKE; Reinhard Nesper; Wolfgang LÖSSLEIN
Original assignee: Sustech Gmbh & Co. Kg
Priority date: 2002-12-27
Filing date: 2003-12-19
Publication date: 2004-07-15
Also published as: DE10261287A1; AU2003300534A1; WO2004059763A3; AU2003300534A8

Abstract

The invention relates to a method for producing a particle-shaped titanium (IV) oxide material, said titanium (IV) oxide material being obtained according to said method. The invention also relates to a sodium titanate with a fibrous morphology which can be used as an educt in said method, and to a method for the production thereof.

Description

Titanium (IV) oxide material as electrode material in batteries

The present invention relates to a process for the production of a particulate titanium (IV) oxide material, the titanium (IV) oxide material obtainable by this process, a sodium titanate with a fibrous morphology which can be used in the process as a starting material, and a process for the production thereof ,

Non-aqueous electrochemistry and photoelectrochemistry have recently produced a large number of products, some of which have found widespread use. These include in particular batteries (primary cells) and accumulators (secondary cells), such as Lithium-ion and magnesium-ion batteries and accumulators, which have a complex profile of requirements with regard to their electrical and mechanical properties. For example, the electronics industry is demanding new, small, lightweight rechargeable batteries (= accumulators) with high capacity and cycle stability. Such rechargeable batteries are of particular interest for the automotive sector and could be used in the future, for example, as starter batteries for conventional automobiles or as a power source in electrically operated vehicles.

It is known to use graphite as the electrode material in rechargeable Li-ion batteries. Due to its layered crystal lattice, graphite has anisotropic, electrical conductivity and is still able to form special forms of intercalation connections, so-called intermediate lattice or intercalation connections. A major disadvantage when using graphite in lithium-ion batteries is the slow speed of the lithium-ion exchange. As a result, briefly available high current densities, as are required, for example, in starter batteries for automobiles, are not achieved.

It is also known to use titanium dioxide in the form of the anatase modification for the production of electrode materials. It has been shown that the Li ion exchange rates achieved with electrodes based on TiO 2 and the consequent The achievable current densities depend crucially on the morphology of the titanium dioxide used.

S. Y. Huang et al. describe in Active and Passive Elec. Comp., 1996, 19, pp. 189-198 the influence of the particle size of the anatase used for electrode manufacture on the current densities of lithium-ion batteries. Thereafter, the storage capacity and the rate of ion exchange increase with decreasing particle size and increasing surface area of the particles.

L. Kavan et al. describe in J. Phys. Chem. B 2000, 104, p. 12012-12020 the electrochemical properties of special thin-film electrodes based on anatase. To produce the anatase used in these electrodes, TiCl ₄ is hydrolyzed in the presence of a polyalkylene oxide block copolymer, the resulting electrodes having high lithium ion exchange rates and thus high current densities being achieved. The cyclic voltamograms of these electrodes have two additional peaks compared to conventional lithium electrodes based on anatase, which are attributed to the presence of amorphous TiO ₂ . A disadvantage of these electrodes is that they lose their advantageous electrochemical properties when subjected to thermal or mechanical stress.

L. Kavan et al. describe in J. Elektrochem. Soc. 2000, 147 (8), pp. 2897-2902 the electrochemical properties of electrodes containing lithium ions on the basis of mesoscopic anatase, which is stabilized with zircon. These electrodes have improved thermal stability. Their Faraday capacity is reduced, however, by the presence of the zircon.

Recently, various reports have been made about magnesium-ion batteries and in particular about prototypes of magnesium-ion secondary cells (see Adv. Mater. 15, 2003, pp. 627-630 and the literature cited there). There as well as in US 6,316,141 and in Chem. Mater. 14, 2002, pp. 2767-2773 teach Chevrel phases M _x Mo ₆ S ₈ (M = metal, e.g. magnesium) as electrode materials. JP 2002100344 describes a mixed oxide containing titanium and its use as an electrode material in magnesium-ion batteries.

In electrical components, e.g. In lithium-ion batteries, magnesium-ion batteries and corresponding rechargeable batteries, multi-layer electrode materials with very small layer thicknesses are increasingly being used, which are also frequently wound up. Furthermore, batteries are often pressed together under high pressure during their manufacturing process. In addition, many electrode materials are exposed to higher temperatures due to their use. There is therefore a great need for electrode materials which have very good electrical application properties and which are not lost even under mechanical or thermal stress.

JP-A-53052737 describes a process for the production of anatase fibers by hydrothermal treatment of potassium titanate in acid solution at 100 to 600 ° C.

JP-A-53028099 describes the hydrothermal conversion of potassium titanate fibers into anatase fibers in acidic solution. The resulting fibers had a specific surface area of 12 m ² / g.

JP-A-10291922 describes the production of titanium dioxide particles in the form of spindles or needles with a diameter of 0.005 to 0.01 μm and a length of 0.01 to 0.5 μm by hydrolysis and tempering of titanyl sulfate. The titanium dioxide particles are used in sunscreens.

JP-A-54010300 describes the production of anatase fibers from titanium tetrachloride hydrolyzates with urea or ammonia.

T. Kasuga et al. describe in Langmuir 14, 3160 - 3163 (1998) TiO ₂ nanotubes with a specific surface area of about 400 m ² g ^"1. For their preparation, SiO ₂ -containing TiO ₂ powder obtained by a sol-gel process is treated with aqueous sodium hydroxide solution in order to remove the SiO ₂ .

CN-A-1151969 describes a process for the production of potassium titanate fibers by hydrothermal treatment of anatase with potassium hydroxide solution.

The object of the present invention is to provide an electrode material with good electrical and mechanical properties. In particular, the electrode materials should have high capacities and good electrokinetic properties, in particular with regard to the incorporation of lithium ions or magnesium ions, in order to ensure high current densities. Furthermore, these materials should have good cycle stability, i.e. maintain their properties even after many charging and discharging processes. Furthermore, these advantageous properties are to be retained even under mechanical and / or thermal loading.

This object was surprisingly achieved by a particulate titanium (IV) oxide material which has a BET surface area above 30 m ² / g and which can be obtained by a process in which i) a doped or undoped sodium titanate with a fibrous morphology provides ii) the doped or undoped sodium titanate into a doped or undoped

Transferred titanium oxide hydrate and iii) treated the product from step ii) under hydrothermal conditions with water or a dilute aqueous acid.

The present invention thus relates to such a titanium (IV) oxide material and to the process for its production described here.

The particulate titanium (IV) oxide material according to the invention can be used as an electrode material in batteries, in particular in lithium ion and magnesium ion batteries. It has been shown that, depending on the reaction time in step iii), materials with different crystallographic properties are obtained. Both materials have the electrochemical properties, in particular the high capacity, the cycle stability, the advantageous kinetic properties with regard to the lithium ion incorporation and the magnesium ion incorporation.

In the case of prolonged treatment in step iii), a material is obtained which comprises: a) crystalline regions A composed of optionally doped titanium dioxide with anatase structure and b) different regions B thereof, which consist of an oxidic, optionally doped titanium (IV) material which is different from titanium dioxide with anatase, brookite or rutile structure.

The proportion of crystalline regions with anatase structure is generally at least 1% by weight, preferably at least 5% by weight and in particular at least 10% by weight. In addition to regions A, such a material has up to 99% by weight, preferably up to 95% by weight and in particular up to 90% by weight, of regions of a further oxidic titanium (IV) phase B. The exact structure of this phase has not yet been determined. However, it can be excluded that phase B is a crystalline titanium dioxide phase with anatase structure or a crystalline titanium dioxide phase with brookite or rutile structure. Phases B may be amorphous titanium dioxide or unconverted titanium (IV) oxide hydrate. In addition to the anatase phases A and the phases B, crystalline phases different from A and B, such as rutile or brookite, can also be present in the titanium (IV) oxide material according to the invention. However, their proportion will generally be less than 40% by weight.

For suitability as electrode material in lithium-ion batteries, magnesium-ion batteries and corresponding accumulators, it has proven to be particularly advantageous if the proportion of areas in phase B is at least 20 % By weight and in particular at least 30% by weight of the titanium (IV) oxide material according to the invention. The proportion of areas A need not be very high and is generally at least 1% by weight, in particular at least 5% by weight and especially at least 10% by weight. Accordingly, a preferred embodiment of the invention relates to a particulate titanium (IV) oxide material which comprises 1 to 80% by weight, in particular 5 to 70% by weight and especially 10 to 70% by weight of crystalline regions A with anatase structure and 20 comprises up to 99% by weight, in particular 30 to 95% by weight and especially 30 to 90% by weight, of areas of phase B. In addition, the titanium (IV) oxide material according to the invention can comprise up to 40% by weight of phases different from phases A and B. However, this proportion will often be less than 20% by weight and in particular less than 5% by weight. The weight fractions of the various titanium (IV) oxide phases given here relate to the phase fractions which can be determined by means of X-ray powder diffractometry (XRD).

With a shorter treatment time, an essentially, i.e. Material consisting of more than 95% titanium (IV) oxide hydrate, which also has the advantageous electrochemical properties mentioned above.

In the titanium (IV) oxide phases and in the titanium (IV) oxide hydrate, some of the titanium atoms can be replaced by atoms of at least one doping metal. The proportion of doping metal will generally not be more than 25 mol%, based on the total amount of titanium and doping metal, and is generally in the range from 0.1 to 25 mol% for the doped titanium (IV) oxide materials according to the invention. % and in particular in the range of 1 to 10 mol%. Examples of suitable doping metals are hafnium, zirconium, tin, germanium, aluminum, gallium, vanadium, niobium and tantalum. With regard to the use of the material according to the invention as an electrode material in lithium-ion batteries, magnesium-ion batteries and accumulators, zirconium and tin are preferred as doping metals.

It has been shown that the titanium (IV) oxide material according to the invention is generally an agglomerate of primary particles. These primary particles generally have particle sizes in the range from 5 to 500 nm, often in the range from 10 to 200 nm and in particular in the range from 20 to 100 nm. The values given here relate to the values which have 90% of the particles (determined by means of TEM = transmission electron microscopy).

These agglomerates generally have a needle-like or fibrous morphology. The length of the fibers or needles is generally not more than 100 μm and in particular not more than 60 μm (values which are exceeded by less than 10% of the fiber particles, determined by means of TEM). The diameter, which at least 90% of the fiber particles have, is generally in the range from 10 to 1000 nm and in particular in the range from 20 to 600 nm. The mean (number average, determined by means of TEM) is frequently 50 to 500 nm and in particular 100 to 300 nm. The length / diameter ratio is generally at least 10: 1 and in particular at least 20: 1 (value that at least 90% of the particles meet). When the titanium (IV) oxide material according to the invention is comminuted (for example by mortar), the advantageous properties, in particular the high capacity, the cycle stability, the advantageous charge kinetics and the stability of the electrochemical properties under mechanical and / or thermal loading, are not lost.

The material according to the invention is further characterized by a high specific surface area (BET surface area, determined in the usual way by means of a Quantachrom Autosorb 3B device or an ASAP 2010 device from Micretrics: determination of the nitrogen adsorption isotherm at 77 K) of preferably at least 40 m ² / g and in particular at least 50 m ² / g. The BET surface area can be up to 250 m ² / g and is in particular in the range from 50 to 200 m ² / g.

To produce the titanium (IV) oxide material according to the invention, a doped or undoped sodium titanate (IV) with a fibrous morphology is first provided. Sodium titanate (IV) is understood to mean the sodium salts of titanium (IV) acids. These can usually be determined using the general formula Na ₂ O- (TiO ₂ ) _n . wherein n has values in the range from 0.5 to 10 and in particular in the range from 0.5 to 3. In principle, any sodium titanate with a fibrous morphology can be used to produce the titanium (IV) oxide material according to the invention. The individual fibers of the fibrous sodium titanate can have lengths of less than 1 μm to several mm, for example in the range from 1 μm to 1 mm.

Basically, a fibrous sodium titanate is obtained by treating a titanium (IV) precursor with sodium hydroxide solution under hydrothermal conditions. The expert understands hydrothermal conditions to be reactions in water, aqueous acids or aqueous bases at temperatures above 100 ° C. in closed vessels, that is to say at pressures above 1 bar (see Römpp, Chemielexikon, 10th edition, Georg-Thieme-Verlag, Stuttgart, 1998 p. 1842).

To produce an undoped sodium titanate, the titanium (IV) precursor alone, in the case of a doped sodium titanate the titanium (IV) precursor together with the desired amount of at least one compound of the doping metal, is subjected to the hydrothermal treatment with sodium hydroxide solution. Such methods are known in principle from the prior art described at the outset and can be used in an analogous manner for the production of doped and undoped sodium titanate.

Suitable titanium (IV) precursors include hydrolyzable titanium (IV) compounds. These include covalent hydrolyzable titanium (IV) compounds, such as titanium (IV) halides, for example titanium tetrachloride, titanium (IV) alcoholates, for example tetrakis-Ci-Cβ-alkyl orthotitanates such as tetraethyl orthotitanate, tetraisopropyl orthotitanate, tetra-n-butyl orthotitanate and the like , hydrolyzable titanium (IV) salts, such as titanyl sulfate and titanium (IV) sulfate (= Ti (S0 ₄ ) ₂ ). Suitable titanium (IV) precursors also include titanium (IV) oxides such as rutile, anatase and brookite.

Sodium titanate with a fibrous morphology has been variously described in the prior art. For example, JP-A-09208398 describes fibrous sodium titanate with a length of at least 150 μm which passes through Treating anatase with aqueous sodium hydroxide solution at temperatures in the range of 250 to 350 ° C is obtained. This fibrous sodium titanate can in principle be used to produce the titanium (IV) oxide material according to the invention.

It has proven to be advantageous to use a fibrous doped or undoped sodium titanate in which less than 10% of the fiber particles have lengths above 100 μm. The length / diameter ratio of the fiber particles of the sodium titanate is generally at least 10: 1 and in particular at least 20: 1 (value which at least 90% of the sodium titanate particles have). The diameter, which at least 90% of the fiber particles have, is generally not more than 2 μm and is in particular in the range from 10 to 1000 nm and especially in the range from 20 to 600 nm. Such a fibrous sodium titanate, doped or undoped, is new and also the subject of the present invention.

This novel sodium titanate is produced by treating a hydrolyzable titanium (IV) compound, in the case of a doped material by treating a mixture of a hydrolyzable titanium (IV) compound with at least one hydrolyzable compound of the desired doping metal, with aqueous sodium hydroxide solution under hydrothermal conditions.

The reaction temperature will generally not exceed 600 ° C. and is preferably at least 150 ° C. and is in particular in the range from 150 ° C. to 350 ° C.

The concentration of the sodium hydroxide solution used is generally at least 1 mol / l and will generally not exceed 15 mol / l. The concentration is in particular in the range from 2 mol / l to 13 mol / l and particularly preferably in the range from 4 mol / l to 11 mol / l. It goes without saying that the manufacture of the fibrous sodium titanate is carried out in closed vessels. The reaction pressure is accordingly determined by the reaction temperature.

The reaction time in the production of the sodium titanate fibers according to the invention is in the range from a few hours to several days, for example in the range from 2 hours to 5 days and in particular in the range from 4 hours to 24 hours.

The starting materials for the production of the sodium titanate fibers according to the invention are the above-mentioned hydrolyzable titanium (IV) compounds, comprising the above-mentioned hydrolyzable, covalent titanium (IV) compounds and hydrolyzable titanium (IV) salts, such as titanyl sulfate and titanium ( IV) sulfate.

Suitable hydrolyzable compounds of the dopant metal in particular the halides and sulfates of the doping metals, especially the chlorides of the doping metals, such as hafnium tetrachloride, zirconium tetrachloride, tin tetrachloride, Ger- maniumtetrachlorid, aluminum trichloride, niobium pentachloride, niobium tetrachloride, as well as the alkoxides, especially those alkoxides of Ci-Cio-alkanols , into consideration. In addition, salts and hydrates such as tin tetrachloride pentahydrate are also suitable for the production of doped sodium titanate fibers according to the invention.

In step ii) of the method according to the invention, the fibrous sodium titanate provided in step i), which can be doped or undoped, is converted into the titanium oxide hydrate. This is achieved in a manner known per se by treating the sodium titanate provided in step i) with aqueous acid. Here, the sodium ions of the sodium titanate are replaced by protons, which are provided by the acid. The sodium salt of the acid formed is washed out. The treatment is usually carried out by washing several times with the aqueous acid. The concentration of the acid is generally in the range from 0.01 mol / l to 12 mol / l and in particular in the range from 0.1 mol / l to 6 mol / l. In principle, aqueous solutions of mineral acids, such as hydrochloric acid, nitric acid and sulfuric acid, and aqueous solutions of organic, water-soluble acids such as acetic acid, formic acid and the like are suitable as aqueous acids. Aqueous mineral acids are preferably used.

As a rule, the sodium titanate is treated with acid at temperatures below 100 ° C. and in particular below 50 ° C.

Treatment usually involves washing several times with acid and / or suspending the sodium titanate in acid. The titanium (IV) oxide hydrate thus obtained is then separated from the acid, for example by filtration, and washed neutral with water.

The titanium (IV) oxide hydrate obtained in step ii) is new, insofar as less than 10% of the fiber particles have lengths above 100 μm, and is likewise a subject of the present invention as a preferred intermediate. The length / diameter ratio of the fiber particles of the titanium (IV) oxide hydrate is generally at least 10: 1 and in particular at least 20: 1 (value which at least 90% of the titanium (IV) oxide hydrate particles have). The diameter, which at least 90% of the fiber particles have, is generally not more than 2 μm and is in particular in the range from 10 to 1000 nm and especially in the range from 20 to 600 nm. It is produced by treating the sodium titanate according to the invention with conditions specified for step ii). The BET surface area of this titanium oxide hydrate according to the invention is generally 5 to 30 m ² / g.

The doped or undoped titanium oxide hydrate obtained in step ii) is then treated in step iii) under hydrothermal conditions with water or a dilute aqueous acid. In principle, the acids mentioned are the mineral acids and organic acids mentioned in step ii). Mineral acids are also preferred here. If an acid is used, its concentration is usually at least 0.01 mol / l and is preferred do not exceed a value of 1 mol / l. In particular, the concentration of the acid is in the range from 0.01 mol / l to 0.5 mol / l and especially in the range from 0.02 mol / l to 0.2 mol / l. Instead of the dilute aqueous acid, water can also be used.

Step iii) is usually carried out at temperatures of at least 100 ° C., preferably at least 120 ° C., in particular at least 150 ° C. and particularly preferably at least 180 ° C. The reaction temperature is generally at most 600 ° C, preferably at most 400 ° C and in particular at most 300 ° C.

By briefly treating the titanium (IV) oxide hydrate obtained in step ii) under the conditions specified for step iii), it is possible to produce a titanium (IV) oxide hydrate whose BET surface area is above 30 m ² / g and in particular in the range from 40 to 250 m ² / g. The duration of the treatment is generally less than 30 minutes and preferably in the range from 1 to 15 minutes. The reaction temperatures are in particular below 200 ° C. and particularly preferably in the range from 100 to 180 ° C. To produce such a titanium (IV) oxide hydrate, the product obtained in step ii) is preferably treated with water. The proportion of titanium (IV) oxide hydrate in the material thus obtained is at least 95% by weight. Surprisingly, it has been shown that such a titanium oxide hydrate also has advantageous electrochemical properties, in particular a high capacity, good cycle stability and advantageous electrokinetic properties.

If the duration of the implementation in step iii) is at least 15 min. is preferably at least 0.5 h and in particular at least 1 h, a material according to the invention is obtained which has the phase components A and B. As a rule, the treatment time in step iii) will not exceed 24 hours and preferably 12 hours. Longer reaction times as well as higher reaction temperatures result in an increase in the proportion of the anatase phase and a decrease in the phase proportion of B. At the same time, a longer reaction time or an increased reaction temperature generally leads to a decrease in the specific see surface along. Likewise, the reaction in a dilute aqueous acid leads to a faster decrease in the specific surface area and a faster decrease in the phase fractions of B compared to the reaction with water.

The titanium (IV) oxide material according to the invention is particularly suitable as an electrode material and especially as an anode material for lithium-ion batteries and accumulators and as an electrode material for magnesium-ion batteries and accumulators. The titanium (IV) oxide materials according to the invention have comparable electrochemical properties to those of Kavan et al. in J. Electrochem. Soc. 147 (2000) pp. 2897-2902 and J. Phys. Chem. B. 104 (2000) p. 12012-12020 described mesoscopic titanium (IV) oxide materials with anatase phase components. In cyclic voltametric investigations of the titanium (IV) oxide materials according to the invention in electrolyte solutions containing lithium ions, two peaks in the range from 1.45 to 1.65 V, in particular one peak each in the range from 1.50 to 1.54 V and in Range from 1, 57 to 1, 6 V. The potential values given here relate to the according to the by Kavan et al. (loc. cit.) method described values (cyclic voltametric investigations of the electrode material in a one-molar solution of LiN (CF ₃ SO ₂ ) ₂ in ethylene carbonate: dimethoxyethane (1: 1 v: v) at scan speeds in the range of 0.01 mV / s to 10 mV / s). In addition, for the material which has an anatase phase A, the peak of lithium insertion customary for anatase is also found in the range from 1.7 V to 2.2 V, especially in the range from 1.8 to 2.0 V (also against lithium as reference electrode). Unlike that of Kavan et al. Mesoscopic titanium (IV) oxide described and that of Kavan et al. The zirconium-stabilized titanium (IV) oxide described does not lose the titanium (IV) oxide materials according to the invention these advantageous properties even under thermal and / or mechanical stress, which makes them particularly suitable for use in lithium batteries and accumulators.

Furthermore, the materials according to the invention have a high capacity and better electrokinetic properties, in particular a faster charge exchange, which enables higher current densities. In addition, the inventive materials have a high cycle stability, in particular materials which contain doping metals. In addition, the titanium (IV) oxide materials according to the invention can be produced much more easily than those of Kavan et al. described materials.

Without being bound by any theory, it is assumed that phase B of the materials according to the invention and the titanium (IV) oxide material obtained in step iii) with short-term treatment are represented by the general formula H ₂ O-nTiO ₂ with n = 2 to 8 and that this phase is responsible for the advantageous electrochemical properties of the materials according to the invention.

The materials according to the invention are therefore particularly suitable for producing electrodes, in particular anodes, and especially electrodes for lithium-ion batteries, for magnesium-ion batteries and for corresponding rechargeable batteries.

The titanium (IV) oxide materials according to the invention can consequently be used as electrode material in batteries, in particular as anode material, and particularly preferably as anode material in lithium ion batteries, i.e. H. Batteries which comprise a non-aqueous, in particular solid, electrolyte which contains lithium ions are used. The titanium (IV) oxide materials according to the invention can also be used as electrode material, e.g. B. as anode material in magnesium ion batteries, that is, in batteries which comprise a non-aqueous, preferably solid electrolyte which contains magnesium ions.

Electrodes, in particular anodes for lithium-ion batteries, for magnesium-ion batteries and for corresponding rechargeable batteries, which comprise a titanium (IV) oxide material according to the invention, can be produced in a manner known per se, the production being essentially based on Shape of the desired electrode and the type of battery to be manufactured. Basically, you can follow the manufacturing instructions for electrodes made of anatase, carbon or carbon-containing materials. The- like methods are for example from Wakihara et al. (Editor) in "Lithiumion Batteries", 1st edition, Wiley VCH, Weinheim, 1998, known. As a rule, in addition to the titanium (IV) oxide material according to the invention, such electrodes comprise one or more electrical contacts, optionally a carrier and optionally a binder for solidifying the titanium (IV) oxide material according to the invention.

Examples of suitable binders are hydroxypropyl cellulose, carboxymethyl cellulose, polythiophene, hydroxyethyl cellulose, polyaniline, polyisothionaphthalene, polyacetylene and their derivatives. For the rest, reference is made to the relevant prior art.

Lithium-ion batteries and magnesium-ion batteries, in particular secondary cells, the anode of which comprises at least one particulate titanium (IV) oxide material according to the invention usually have, in addition to such an anode, at least one cathode and one non-aqueous electrolyte which contains lithium ions or magnesium ions, on. Concerning. the cathode materials, the electrolyte systems and the structure of the batteries are based on the relevant prior art, for example on Wakihara et al. (loc. cit.) and Adv. Mater. 15, 2003, p.627 ff., US 6,316,141 and literature cited therein.

The following figures serve to further explain the invention:

Figure 1: Cyclic voltammogram of material no. 21: Electrolyte solution: 1M LiN (CS ₃ SO ₂ ) ₂ in ethylene carbonate / dimethoxyethane (1: 1 v: v) at a scan speed of 0.1 mV / s. and a plot of the anodic peak current versus scan speed

FIG. 2: plot of the capacitive charge component of the S peaks, determined by integrating the S peaks of the anodic branch of a cyclic voltammogram, as shown in FIG. 1, as a function of the proportion of the phase regions B and based on the total capacity. Figure 3: Relative charge capacity (determined by integrating the anodic branch of a cyclic voltammogram, as shown in Figure 1 and normalized to the charge capacity at 0.1 mV / sec), plotted as a function of the scan speed, for materials No. 7 (circles ), Material No. 8 (squares), commercial nanocrystalline anatase C 240, manufactured according to JES 143 (1996) p. 395.

The following examples are intended to explain the invention, but are not to be understood as restrictive.

Example 1: Synthesis of sodium titanate fibers starting from TiCl ₄

8 ml (72.9 mmol) of TiCl ₄ were hydrolyzed in 20 ml of demineralized water and made up to 150 ml with 10 N sodium hydroxide solution. The reaction mixture was placed in a 250 ml Teflon vessel and heated to 250 ° C for 6 h. The product consisted of sodium titanate fibers with a length of <100 μm and a diameter of 30 to 1000 nm, on average about 300 nm.

Example 2: Synthesis of sodium titanate fibers starting from titanium alkoxide

21.6 g (72.9 mmol) of tetraisopropyl orthotitanate were added dropwise with stirring in 50 ml of 10 N sodium hydroxide solution, made up to 100 ml total volume with 10 N sodium hydroxide solution and heated in a 200 ml Teflon vessel in an autoclave at 250 ° C. for 12 hours. The product consisted of sodium titanate fibers with a length of <100 μm and a diameter of 30 to 1000 nm, on average about 300 nm.

Example 3: Synthesis of sodium titanate fibers starting from titanium oxide sulfate

20 g (125 mmol) of titanium oxide sulfate were suspended in 40 ml of water. The suspension was placed in a 200 ml Teflon vessel and made up to 150 ml with 10 N sodium hydroxide solution. The mixture was then heated to 250 ° C. in the autoclave for 12 h. The product consisted of sodium titanate fibers with a length of <100 μm and a diameter of 30 to 1000 nm, on average about 300 nm. Example 4: Synthesis of sodium titanate fibers starting from anatase

In a 200 ml Teflon vessel, 5 g (62.5 mmol) of anatase with 10 ml of 10 N sodium hydroxide solution were heated in an autoclave at 250 ° C. for 96 h. A continuous fleece of fibers with a length of> 1 mm and a diameter of 300 to 3000 nm had deposited on the wall of the vessel.

Example 5: Synthesis of Zr-doped sodium titanate fibers

8 ml (72.9 mmol) of TiCl ₄ were hydrolyzed in a solution of 1 g (4.35 mmol) of ZrCl ₄ in 20 ml of demineralized water and made up to 150 ml with 10 N sodium hydroxide solution. The reaction mixture was placed in a 250 ml Teflon vessel and heated to 250 ° C for 6 h. The product consisted of doped sodium titanate fibers with a length of <100 μm and a diameter of 30 to 1000 nm, on average about 300 nm.

Example 6: Synthesis of Sn-doped sodium titanate fibers

8 ml (72.9 mmol) of TiCl ₄ were hydrolyzed in a solution of 1.7 g (4.35 mmol) of SnCl ₄ * 5H ₂ O in 20 ml of demineralized water and made up to 150 ml with 10 N sodium hydroxide solution. The reaction mixture was placed in a 250 ml Teflon vessel and heated to 250 ° C for 6 h. The product consisted of doped sodium titanate fibers with a length of <100 μm and a diameter of 30 to 1000 nm, on average about 300 nm.

Example 7: Conversion of sodium titanate fibers to titanium oxide hydrate fibers

Sodium titanate fibers, produced according to Examples 1-6, are washed several times with aqueous hydrochloric acid (5 N). Here, the sodium ions are exchanged for protons. The titanium oxide hydrate fibers obtained in this way are then washed neutral with water. When using the sodium titanates of Examples 1 to 3, 5 and 6, titanium (IV) oxide hydrate fibers with a length of <100 μm and a diameter of 30 to 1000 nm were obtained, on average about 300 nm. The BET surface area the materials thus obtained were in the range of 5 to 25 m ² / g in all cases.

Examples 8 to 24:

Production of the titanium (IV) oxide material according to the invention

Sodium titanate fibers, produced according to Example 1 or according to Example 5, were converted into the oxide hydrate as described in Example 7. The hydrated oxide fibers were suspended in a liquid and heated in an autoclave. Details can be found in Table 1 below. The products consisted of fibers with a length of <60 μm and a diameter of 20 to 600 nm, on average 150 nm.

Table 1:

comparison

* The Zr-doped sodium titanate from Example 5 was used as the starting material.

1) The proportion of phase B different from anatase was determined by means of powder X-ray diffractometry in accordance with the method of Banfield et al. (H. Zang, M. Finegann and JF Banfield, Nanoletters, 1, 81 (2001)), using rutile as an internal standard with 3.7% by weight of anatase as an impurity (Bayer RUF). The powder X-ray diffractometric tests were carried out with a Siemens D-5000 diffractometer using CuK _α radiation. 2) The BET surface area of samples 12 to 24 was determined using an ASAP 2010 Micrometrics instrument (determination of the nitrogen adsorption isotherm at 77 K).

Comparative Example 1: Hydrothermal conversion of potassium octatitanate

5 g (6.8 mmol) of potassium octatitanate (Otsuka Chemicals, Lot 2A96I) were treated with hydrochloric acid as described in Example 7 and then heated in an autoclave with 100 ml of 0.1 N hydrochloric acid at 250 ° C. for 1 hour. No reflexes of anatase were observed in the X-ray powder diagram (XRD).

Comparative Example 2: Hydrothermal Reaction of Potassium Titanate (Produced According to CN 1151969)

1.53 g (19 mmol) of anatase (Acros, Lo A014127201), 26.93 g (480 mmol) of potassium hydroxide (Riedel de Haen, Lot 92990) and 16 ml of water were heated in an autoclave at 200 ° C. for 4 h. In addition to fibers, the product contained water-soluble crystalline components. The product was converted into the oxide hydrate as described in Example 7 and heated in an autoclave with 100 m 0.1 N hydrochloric acid at 200 ° C. for 1 h. After XRD, the product consisted of phase-pure anatase, but fibers were no longer observed in the TEM, instead the sample consisted of platelets with an average edge length of 60 nm.

Electrochemical investigations:

1. Manufacture of the electrodes

Powder samples were processed in aqueous medium to viscous pastes according to known methods (L. Kavan, B. O'Regan, A. Kay and M. Grätzel, J. Electroanal. Chem., 346, 291 (1993); MK Nazeeruddin, A. Kay, I. Rodicio, R. Humphry-Baker, E. Mueller, P. Liska, N. Vlachopolous and M. Grätzel, J. Am. Chem. Soc, 115, 6382 (1993)). For this purpose, 0.3 g of the powder was mixed with 0.8 ml of a 10% strength by weight aqueous solution of acetylacetone. 0.8 ml of a 4% strength by weight aqueous solution of hydroxypropyl cellulose (M _w 100000 Dalton) and then 0.4 ml of a 10% strength by weight aqueous solution of Triton-X100 (Fluka ). The resulting slurry was then carefully homogenized with stirring and, if necessary, diluted with a little water. Titanium mesh (5 x 15 mm, Goodfellow) served as the electrode carrier. The titanium nets were immersed in slurry of the titanium oxide material so that the coated area was approximately 5 x 5 mm in size. The electrodes thus obtained were dried in air and then calcined at 450 ° C. for 30 minutes while admitting air.

Electrodes were also made by placing the slurry on a layer of conductive glass (F-doped Sn0 ₂ : TEC 8 from Libbey-Owens-Ford, 8 Ω / cm ² ) using a doctor blade technique (SD Burnside, J. Moser , K. Brooks, M. Grätzel and D. Cahen, J. Phys. Chem. B, 103, 9328 (1999)) applied. The carrier made of conductive glass had a size of 3 x 5 x 0.3 cm ³ . An adhesive tape on both ends of the carrier (0.5 cm) on the one hand gave the coating thickness and left parts of the carrier uncovered for the purpose of electrical contact. The coating applied to this support was then calcined at 450 ° C. for 30 minutes. The support coated in this way was cut into 10 electrodes of size 1.5 × 1 cm ² . The area of the coating was approximately 1 x 1 cm ² .

2. Cyclic voltammetric studies

The electrochemical investigations were carried out in a cell with a compartment, using a potentiostat Autolab Pgstat-20 (ecochemistry) with GPES-4 software. Lithium metal served as reference and auxiliary electrodes, so that the potentials are related to Li / Li ⁺ (1 M) as reference electrode. The LiN (CF ₃ S0 ₂ ) _{2 used} (Fluorad HQ 115 from 3M) was dried at 130 ° C. and 1 mPa. ethylene Carbonate and 1,2-dimethoxyethane were dried over 4A molecular sieve (Union Carbide).

A 1 molar solution of LiN (CF ₃ S0 ₂ ) ₂ in ethylene carbonate / dimethoxyethane (1: 1 v: v), which contained 15 to 40 ppm water, was used as the electrolyte solution (determined by Karl Fischer titration). All investigations were carried out in a "glove box".

FIG. 1 shows the result of a cyclovoltametric examination of material no. 21. In contrast to voltammograms of normal anatase, the cyclic voltammogram shows 2 pairs of peaks (S1 and S2). The potentials of S1 and S2 are 1.52 and 1.59 vs. Li / Li ⁺ . The remaining pair of peaks at about 1.8 V is usually observed in anatase electrodes.

The materials 13 to 22 given in Table 2 show 2 peaks at approximately 1.52 and 1.59 V with different intensities. Such a peak is not observed for material 12. These peaks are observed in the zirconium-doped material 23 as well as in the titanium oxide hydrate material 24.

A plot of the size of the capacitive charge component of the S1 / S2 peaks, determined by integrating the S1 / S2 peaks of the anodic branch of a cyclic voltammogram (based on the total charge capacity) as a function of the proportion of components B in the respective material, shows that with increasing B component of the capacitive charge component of the S1 / S2 peaks increases (see FIG. 2).

In Figure 3, the total charge capacity (determined by integrating the anodic branch of a cyclic voltammogram as shown in Figure 1) of Materials Nos. 18, 19 and 21 is plotted against the scan speed. For comparison purposes, the same curve was also shown for nanocrystalline anatase (C 240, 89 m ² / g), produced by a sol-gel process. Since the absolute charge capacity of each test electrode varied (between 100 and 180 mC), the data shown in FIG. standardization of the respective electrode at the lowest scan speed (0.1 mV / S).

It can be seen from FIG. 3 that materials 18, 19 and 21 according to the invention ensure this charge even at high scanning speeds of 1 to 2 mV / S. In contrast, the material, which consists exclusively of anatase, shows a decreasing capacity with increasing scanning speed.

To investigate the cycle stability, cyclic voltammograms in the range from 1.2 V to 2.5 V were recorded several times in succession and the specific capacity of the S peaks was determined. In the case of the undoped material, the decrease in the specific capacity after 20 cycles was less than 10% and in the case of the zirconium-doped material 23 it was less than 5%. No significant decrease in capacity was observed for titanium (IV) oxide hydrate from Example 24 even after 35 cycles. For a material consisting only of anatase, such as material 12, the decrease after 20 cycles was more than 30%.

Claims

claims

1. Particulate titanium (IV) oxide material with a BET surface area above 30 m ² / g, obtainable by a process in which

i) providing a doped or undoped sodium titanate with a fibrous morphology, ii) converting the doped or undoped sodium titanate into a doped or undoped titanium oxide hydrate, and iii) treating the product from step ii) with water or a dilute aqueous acid under hydrothermal conditions.

2. A particulate titanium (IV) oxide material according to claim 1 comprising:

a) crystalline regions A of optionally doped titanium dioxide with anatase structure and b) different regions B thereof, which consist of an oxidic, optionally doped titanium (IV) material which is different from titanium dioxide with anatase, brookite or rutile structure,

3. Particulate titanium (IV) oxide material according to claim 2, comprising 1 to 80% by weight of crystalline regions A and 20 to 99% by weight of regions B.

4. Particulate titanium (IV) oxide material according to one of the preceding claims with a BET surface area of at least 40 m ² / g.

5. Titanium (IV) oxide material according to one of the preceding claims, containing, in addition to titanium, at least one doping metal which is selected from hafnium, zirconium, tin, germanium, aluminum and niobium.

6. Particulate titanium (IV) oxide material according to one of the preceding claims, wherein the particles of the titanium (IV) oxide material from agglomerates consist of primary particles in which 90% of the primary particles have a particle diameter in the range from 5 to 500 nm.

7. Particulate titanium (IV) oxide material according to one of the preceding claims, which has a fibrous morphology, wherein no more than 10% of the particles have fiber lengths above 100 microns and the ratio of length to diameter is at least 10: 1.

8. Titanium (IV) oxide material according to one of the preceding claims, wherein at least 70% of the fiber particles of the doped or undoped sodium titanate used in step i) have a length below 100 μm with a ratio of length to diameter of at least 10.

9. titanium (IV) oxide material according to claim 8, wherein in step i) a doped or undoped sodium titanate is provided by treating a hydrolyzable titanium (IV) compound comprising covalent titanium (IV) compounds and hydrolyzable titanium (IV) salts or a mixture of a hydrolyzable titanium (IV) compound with at least one hydrolyzable compound of a doping metal with aqueous sodium hydroxide solution under hydrothermal conditions.

10. A method for producing a titanium (IV) oxide material according to any one of the preceding claims, comprising:

i) providing a doped or undoped sodium titanate with a fibrous morphology, ii) converting the doped or undoped sodium titanate into a doped or undoped titanium oxide hydrate and iii) treating the product from step ii) under hydrothermal conditions with water or an aqueous acid.

11. The method according to claim 10, wherein in step iii) at temperatures in the range of 100 to 300 ° C.

12. The method according to claim 10 or 11, wherein step iii) water or an aqueous acid is used at a concentration of at least 0.01 mol / l.

13. The method according to any one of claims 10 to 12, wherein in step i) a doped or undoped sodium titanate is provided by treating a hydrolyzable titanium (IV) compound comprising covalent titanium (IV) compounds and hydrolyzable titanium (IV) salts or one Mixture of a hydrolyzable titanium (IV) compound with at least one hydrolyzable compound of a doping metal with aqueous sodium hydroxide solution under hydrothermal conditions.

14. The method according to claim 13, wherein the treatment with the aqueous sodium hydroxide solution is carried out at temperatures in the range from 150 to 350 ° C.

15. The method according to claim 13 or 14, wherein the sodium hydroxide solution has a concentration of 2 mol / l to 13 mol / l.

16. Sodium titanate with fibrous morphology, which is optionally doped, wherein at least 70% of the fiber particles have a length below 100 microns with a ratio of length to diameter of at least 10.

17. A process for producing a sodium titanate according to claim 16, characterized in that at least one hydrolyzable titanium (IV) compound comprising covalent titanium (IV) compounds and hydrolyzable titanium (IV) salts or a mixture of at least one hydrolyzable titanium (IV ) compound and at least one hydrolyzable compound of a doping metal treated with aqueous sodium hydroxide solution under hydrothermal conditions.

18. The method according to claim 17, characterized in that the hydrolyzable titanium (IV) compound is selected from titanium (IV) halides, titanium (IV) alcoholates, titanium (IV) sulfate and titanyl sulfate.

19. Titanium (IV) oxide hydrate with a fibrous morphology, which is optionally doped, wherein at least 70% of the fiber particles have a length below 100 μm with a ratio of length to diameter of at least 10.

20. Titanium (IV) oxide hydrate with a BET surface area of at least 40 m ² / g.

21. A method for producing a titanium (IV) oxide hydrate according to claim 19, comprising

i) providing a doped or undoped sodium titanate with a fibrous morphology, wherein at least 70% of the fiber particles have a length below 100 μm with a length to diameter ratio of at least 10 ii) converting the doped or undoped sodium titanate into a doped or undoped titanium oxide hydrate by treatment with acid.

22. The method according to claim 23, wherein to produce the sodium titanate in step i) at least one hydrolyzable titanium (IV) compound comprising covalent titanium (IV) compounds and hydrolyzable titanium (IV) salts or a mixture of at least one hydrolyzable titanium (IV) compound and at least one hydrolyzable compound of a dopant treated with aqueous sodium hydroxide solution under hydrothermal conditions.