DOMINKO ROBERT (SI)
BELE MARJAN (SI)
GABERSCEK MIRAN (SI)
JAMNIK JANKO (SI)
KUZMA MIRJANA (SI)
DOMINKO ROBERT (SI)
BELE MARJAN (SI)
GABERSCEK MIRAN (SI)
JAMNIK JANKO (SI)
| US6103419A | 2000-08-15 |
MARCILLY, C., COURTY, P., DELMON, B.: "preparation of highly dispersed mixed oxides and oxide solid solutions by pyrolysis of amorphous organic precursors", JOURNAL OF THE AMERICAN CERAMIC SOCIETY-DISCUSSIONS AND NOTES, vol. 53, no. 1, 1970, pages 56 - 57, XP002561987
PETRYKIN V ET AL: "Chemistry and Applications of Polymeric Gel Precursors", 1 January 2005, HANDBOOK OF SOL-GEL SCIENCE AND TECHNOLOGY; PROCESSING, CHARACTERISATION AND APPLICATIONS, KLUWER ACADEMIC PUBLISHERS, US, PAGE(S) 77 - 103, ISBN: 9781402079696, XP008119303
CLAIMS
1. Titanates of transition metals as materials for cathodes in lithium batteries, characterized by being made on the basis of titanates of transition metals with a general formula Li 2 MTiO 4 , where M = Mn, Fe, Co, by the sol-gel process, where the starting precursors are iron (III) acetyl acetonate, lithium methoxide, and titanium (IV) isopropoxide, and, as needed, additives that form carbon compounds upon pyrolysis, where 0.001 - 0.01 mole of iron (III) acetyl acetonate is dissolved in 4.5 - 45 niL N,iV-dimethylformamide, and in a second container 0.002 - 0.02 mole of lithium methoxide is separately dissolved in 1.2 - 12 mL 2-methoxyethanol, and in the third container 0.001 — 0.01 mole of titanium (IV) isopropoxide is separately dissolved in 0.6 — 6 mL iV,N-dimethylformamide, and that the solution with lithium ions is poured into the solution with iron (III) ions, the mixture is well stirred, and that the obtained mixture of the two solutions is poured into the solution of titanium (IV) ions, and the obtained solution or sol is left to complete the reaction by stirring for 3 hours, after which 0.004 — 0.04 mL of milliQ water is added to the obtained solution, and simultaneously 0.0014 - 0.014 mole of ethylene glycol is added, after which the obtained gel is placed in a drying oven at 6O 0 C 5 to allow the reaction to be completed, after which it is left standing for approximately 3 days, then it is dried at 6O 0 C in an open container, and the obtained powder is ground in an agate mortar for 10 minutes, after which it is placed in an oven, and is heated in a CO/CO 2 atmosphere (ratio CO : CO 2 = 1 : 1) or an inert atmosphere at a heating rate of 1 - 20°C/min to 800 0 C, after which the obtained product is cooled at a cooling rate of 1 - 20°C/min to room temperature, and is transferred into a drybox with a content of oxygen and moisture below 10 ppm, and is used for the preparation of a cathode.
2. Titanates according to claim 1, characterized by that the starting precursor instead of iron (III) acetyl acetonate is another suitable iron (III) salt.
3. Titanates according to claim I 3 characterized by that the starting precursor instead of iron (III) acetyl acetonate is iron (II) acetyl acetonate or another suitable iron (II) salt.
4. Titanates according to claim I 5 characterized by that the starting precursor instead of iron (III) acetyl acetonate is manganese (II) acetyl acetonate or another suitable manganese (II) salt.
5. Titanates according to claim I 5 characterized by that the starting precursor instead of iron (III) acetyl acetonate is cobalt (II) acetyl acetonate or another suitable cobalt (II) salt.
6. Titanates according to claim 1, characterized by that the baking lasts between 1 minute to 10 hours.
7. Titanates of transition metals as materials for cathodes in lithium batteries, characterized by being made on the basis of titanates of transition metals with a general formula Li 2 MTiO 4 , where M = Mn, Fe, Co, by the citrate process, where the starting precursors are titanium dioxide, lithium hydroxide, and iron (III) citrate, where 0.002 - 0.02 mole of titanium dioxide is dissolved in 9.7 - 97 mL of milliQ water and the colloid solution is dispersed in an ultrasonic bath for approximately 2 hours, after which 0.004 - 0.04 mole of lithium hydroxide is added and the solution is dispersed for another one hour, and that separately 0.002 - 0.02 mole of iron (III) citrate is dissolved in 9.5 - 95 mL of milliQ water at 60°C for approximately one hour. Both solutions, cooled to room temperature, are mixed and dried in a rotary evaporator at 6O 0 C until a viscous liquid is obtained, which is dried in a drying oven at 60 0 C overnight until a powder is obtained; the obtained powder is ground in an agate mortar for 10 minutes, then it is placed in an oven and is heated in a CO/CO 2 atmosphere (ratio CO : CO 2 = 1 : 1) or an inert atmosphere at a heating rate of 1 - 20°C/min to 800 0 C, after which the obtained product is cooled at a cooling rate of 1 - 20°C/min to room temperature, and is transferred into a drybox with a content of oxygen and moisture below 10 ppm, and is used for the preparation of a cathode.
8. Titanates according to claim 7, characterized by that the starting precursor instead of lithium hydroxide is lithium citrate or lithium acetate dihydrate.
9. Titanates according to claim 7, characterized by that the starting precursor instead of iron (III) citrate is cobalt (II) acetate or another suitable cobalt (II) salt.
10. Titanates according to claim 7, characterized by that the starting precursor instead of iron (III) citrate is manganese (II) acetate tetrahydrate or another suitable manganese (II) salt.
11. Material for cathodes in lithium batteries, obtained according to claims 1 to 10, characterized by its use with the addition of a binder and electronic conductor as an electrochemical active cathode material in lithium batteries.
12. Material with a formula Li 2 MTiO 4 (M = Mn, Fe, Co) characterized by that it shows between 20 and 100 % of the theoretical capacity upon electrochemical testing, where theoretical capacity signifies the electrochemical exchange of 2 moles of lithium per 1 mole of Li 2 MTiO 4 (M = Mn, Fe, Co).
13. Material according to claim 11, characterized by that the binder is polytetraflouroethylene, polyvinylidenefluoride, polyimide, ethylene-propylene-diene-terpolymer and similar polymers.
14. Material according to claim 11, characterized by that the electronic conductor is carbon black, graphite, metal particles, or an electrically conductive polymer.
15. The use of the material according to claims 11 and 12 for the preparation of the cathode in lithium batteries.
16. Cathode for lithium batteries, characterized by being made from the material according to claims 11 and 12. |
TITANATES OF TRANSITION METALS AS MATERIALS FOR THE CATHODE IN
LITHIUM BATTERIES
Field of the invention
The presented invention fits in the area of chemical technology, specifically: chemical sources of electrical energy. It relates to the preparation of novel active materials for batteries based on titanates of transition metals with the general formula Li 2 MTiO 4 , where M = Mn, Fe, Co meaning that M = Mn and/or Fe and/or Co, and the preparation of a cathode from the named materials for use in lithium ion batteries.
State of the art
Synthesis of materials Li 2 MTiO 4 , where M = Mn, Fe, Co, Ni
The synthesis of materials with the general formula Li 2 MTiO 4 , where M = Mn, Fe, Co, Ni is described in the paper L. Sebastian, J. Gopalakrishnan, Li 2 MTiO 4 (M = Mn, Fe, Co, Ni): New cation-disordered rocksalt oxides exhibiting oxidative deintercalation of lithium. Synthesis of an ordered Li 2 NiTiO 4 , JOURNAL OF SOLID STATE CHEMISTRY 172 (1): 171-177 APR 2003. The authors used a classical solid state synthesis at high temperatures from 800-900 0 C - high temperature materials. In addition, the analogue Li 2 NiTiO 4 was prepared by a modified procedure at a lower temperature 510 0 C — low temperature Li 2 NiTiO 4 . They were not successful in preparing other analogues by the low-temperature procedure. All high-temperature analogues had a rocksalt structure, whereas low-temperature Li 2 NiTiO 4 had a monoclinic structure.
Electrochemical properties OfLi 2 MTiO 4 materials, where M = Mn, Fe, Co, Ni From the Li 2 MTiO 4 (M = Mn, Fe, Co, Ni) family of materials only the analogue Li 2 NiTiO 4 has been tested electrochemically thus far. The testing is described in the paper by S. R. S. Prabaharan, M.S. Michael, H. Ikuta, Y. Uchimoto, M. Wakihara, Li 2 MTiO 4 - a new positive electrode for lithium batteries: soft chemistry synthesis and electrochemical characterization, Solid State Ionics 172 (2004) 39-45, which shows that the reversible capacity at normalized current in the range from 80-150 mA/g is approx. 80-100 mAh/g. Other analogues form Li 2 MTiO 4 (M = Mn, Fe, Co) have not yet been electrochemically tested. Indirect evidence of
potential electrochemical activity of Li 2 MTiO 4 (M = Mn, Fe, Co) has been indirectly shown by experiments in which these materials were electrochemically oxidized by atmospheric oxygen at 150 0 C, as described in the paper by L. Sebastian, J. Gopalakrishnan, Li 2 MTiO 4 (M = Mn, Fe, Co, Ni): New cation-disordered rocksalt oxides exhibiting oxidative deintercalation of lithium. Synthesis of an ordered Li 2 NiTiO 4 , JOURNAL OF SOLID STATE CHEMISTRY 172 (1): 171- 177 APR 2003. After oxidation the following compounds were formed: LiMnTiO 4 , LiFeTiO 4 , and Li L24 CoTiO 4 . The oxidation of the analogue Li 2 NiTiO 4 is not described in this paper.
Technical problem
One of the goals of preparing modern materials for lithium batteries is to achieve the highest possible energy density of the materials. This means that we wish to store as much electrical energy as possible in a given mass of material with a given volume. If the materials possess a similar standard electrochemical potential, the energy density approximately corresponds to the specific capacity of the material. Cathode materials currently used in lithium batteries have a theoretical specific capacity of up to 140 mAh/g. Materials prepared and tested in laboratory conditions have had theoretical capacities up to 170 mAh/g. The theoretical specific capacity of materials Li 2 MTiO 4 (M = Mn, Fe, Co) is up to 300 mAh/g if it is assumed that both lithium ions in the formula of these compounds can be used electrochemically. Although materials with the general chemical composition Li 2 MTiO 4 (M = Mn, Fe, Co) have already been synthesized as described in L. Sebastian, J. Gopalakrishnan, Li 2 MTiO 4 (M = Mn, Fe, Co, Ni): New cation- disordered rocksalt oxides exhibiting oxidative deintercalation of lithium. Synthesis of an ordered Li 2 NiTiO 4 JOURNAL OF SOLID STATE CHEMISTRY 172 (1): 171-177 APR 2003, it is not known whether these materials should possess any electrochemical activity or any electrochemical capacity.
The solution to the problem is to synthesize materials based on Li 2 MTiO 4 (M = Mn, Fe, Co) that will exhibit significant electrochemical activity. Significant electrochemical activity means that under laboratory testing in an electrochemical cell at least 20 % of the reversible theoretical capacity of the given material is reached. The theoretical and maximum practical capacity of such compounds will be up to 300 mAh/g, which is considerably more than compounds currently employed in Li batteries.
The object of this invention is the synthesis of a new family of materials with the general formula Li 2 MTiO 4 (M = Mn, Fe, Co) exhibiting a significant electrochemical capacity.
The invention solves the technical problem by presenting a family of materials with the formula Li 2 MTiO 4 (M = Mn, Fe, Co) that are prepared either through a modified sol-gel synthesis or through the citrate process according to independent claims. The advantage of both processes over the currently known synthesis in solid state is the homogenization of input compounds on a molecular level. Due to this advantage there is a higher probability that such materials will exhibit significant electrochemical activity and will be potentially useful as cathodes in lithium batteries.
Description of the solution to the problem
The invention will be described by a general description of the solution, with attached schemes, as well as by a description of procedures and execution examples.
General description of the solution
The material Li 2 MTiO 4 , where M = Mn, Fe, Co, meaning that M = Mn and/or Fe and/or Co, is such that it will possess significant reversible capacity, that it has a reversible capacity that is between 20 and 100 % of the theoretical capacity, that it is synthesized by a modified sol gel process or by the citrate process. The first process starts from a M(II) or M(III) salt (M = Mn, Fe, Co), lithium methoxide and titanium (IV) isopropoxide, and if needed, from additives that form carbon compounds upon pyrolysis. The second process starts from titanium dioxide, lithium hydroxide or, alternatively, lithium citrate or acetate and the citrate or acetate of the metal M (M = Mn, Fe, Co) in the oxidation state M(II) or M(III). In both processes the final product is formed through heating in an inert or reducing atmosphere.
The principal novelty in comparison to the previously known classical process with a reaction in solid state is that both new processes start from homogeneous mixtures at the molecular level, while the previous process starts from significantly less homogeneous mixtures. The consequence is that the new processes yield materials with significant reversible capacity, which is at least 20 % of the theoretical capacity. The capacity according to the previous process, described in (L. Sebastian, J. Gopalakrishnan, Li 2 MTiO 4 (M = Mn, Fe, Co, Ni): New cation- disordered rocksalt oxides exhibiting oxidative deintercalation of lithium. Synthesis of an
ordered Li 2 NiTiO 4 , JOURNAL OF SOLID STATE CHEMISTRY 172 (1): 171-177 APR 2003) was negligible.
Description and figures
Figure 1: Powder X-ray diffraction pattern of the material based on Li 2 FeTiO 4 , prepared according to Example D. The powder diffraction pattern shows that the material is predominantly the crystalline compound Li 2 FeTiO 4 .
Figure 2: Capacity of the material based on Li 2 FeTiO 4 , prepared according to Example A. It shows 9 charge/discharge cycles. The current density was 7.38 niA/g of active material. The material gave approximately 30 % of the theoretical capacity at 60 °C.
Figure 3: Capacity of the material based on Li 2 FeTiO 4 , prepared according to Example D. It shows 12 charge/discharge cycles. The current density was 7.38 mA/g of active material. The material gave approximately 80 % of the theoretical capacity at 60 0 C.
Description of novel processes
The process for preparing titanates as cathode materials by the sol-gel method is as follows: a) It starts from M(II) or M(III) salts (M = Mn, Fe, Co), lithium methoxide and titanium (IV) isopropoxide, and additives, as needed, that form carbon compounds upon pyrolysis. b) 0.001 - 0.01 mole of M(II) or M(III) salt (M = Mn, Fe, Co) is dissolved in 4.5 - 45 mL N,iV-dimethylformamide. In a separate container 0.002 - 0.02 mole of lithium methoxide is separately dissolved in 1.2 - 12 mL 2-methoxyethanol. In a third container 0.001 - 0.01 mole of titanium (IV) isopropoxide is separately dissolved in 0.6 - 6 mL N, N- dimethylformamide. The solution with lithium ions is poured into the solution with M(II) or M(III) ions (M = Mn, Fe, Co) and the mixture is thoroughly stirred. The mixture of these two solutions is then poured into the solution with titanium (FV) ions and the final mixture or sol is left to mix for 3 hours. To the final solution (sol) obtained under indent b) 0.004 - 0.04 mole of milliQ water is added, which is needed for the initiation of gelling or for the initiation of hydrolysis and condensation reactions. Simultaneously, 0.0014 - 0.014 mole of ethylene glycol is added, which serves as a
catalyst for gelation or as catalyst for hydrolysis, as well as condensation, and as a carbon source. c) The gel obtained under indent b) is stored in a closed container and is left overnight in a drying oven at 60°C to completely react. After that it is left standing for approximately 3 days (ageing of the gel). Then it is dried at 60°C in an open container or in vacuum or in an inert atmosphere. d) The obtained powder is ground in an agate mortar for 10 minutes. It is then put into an oven and is heated in a CO/CO 2 atmosphere (ratio COiCO 2 = 1 :1) or in an inert atmosphere according to the selected heating program: heating and cooling rate 1 — 20°C/min, maximum temperature 800°C. The heating period is between 1 min and 10 hours. After baking, the material is transferred to a drybox with a content of water and oxygen below 10 ppm. e) The obtained material is used for the preparation of a cathode suitable for electrochemical testing.
In the process described by the invention it is not necessary to use additives that yield carbon compounds upon pyrolysis. If the catalyst for gelation or the catalyst for hydrolysis and condensation does not contain carbon, a compound that gives carbon compounds upon pyrolysis can be used in addition to the catalyst. The mole ratio of ions Li : M : Ti (M = Mn, Fe, Co) in the final solution (sol) is 2±X : Id=X : l±X.
With the addition of a suitable binder (polytetrafluoroethylene, polyvinylidenefluoride, polyimide, ethylene-propylene-diene-terpolymer and similar polymers) and an electronic conductor (carbon black, graphite, metal particles, electronically conductive polymer), the obtained material can be used as an electrochemically active cathode material in lithium batteries.
The process for preparing titanates as cathode materials by the citrate method is as follows: a) it starts from titanium dioxide, lithium hydroxide (alternatively lithium citrate or acetate), and a citrate or acetate of a metal M (M = Mn, Fe, Co) in the oxidation state M(II) Or M(III). b) A colloid solution of 0.002 - 0.02 mole titanium dioxide is prepared in 9.7 - 97 mL milliQ water. It is dispersed in an ultrasonic bath for 2 hours. To the obtained colloid
solution of titanium dioxide 0.004 - 0.04 mole of lithium hydroxide is added and the dispersing is continued for one hour, so that the lithium hydroxide is dissolved. c) Separately, 0.002 - 0.02 mole of M (III) citrate or acetate is dissolved in 9.5 - 95 mL milliQ water at 60°C. d) The solutions obtained under indent b) and c), cooled to room temperature, are mixed. The mixture is dried in a rotary evaporator at 60°C until a viscous liquid is obtained, which is then further dried in a drying oven at 60°C overnight until a powder is obtained, or it is dried in vacuum. e) The obtained powder is ground in an agate mortar for 10 minutes. It is then put into an oven and is heated in a CCVCO 2 atmosphere (ratio CO : CO 2 — 1 : 1) or in an inert atmosphere according to the selected heating program: heating and cooling rate 1 - 20°C/min, maximum temperature 800°C. The heating period is between 1 min and 10 hours. After baking the material is transferred to a drybox with a content of water and oxygen below 10 ppm. f) The obtained material is used for the preparation of a cathode suitable for electrochemical testing.
The mole ratio of ions Li : M : Ti (M = Mn, Fe, Co) in the final solution (sol) is 2±X : l±X : l±X. With the addition of a suitable binder (polytetrafluoroethylene, polyvinylidenefluoride, polyimide, ethylene-propylene-diene-terpolymer and similar polymers) and an electronic conductor (carbon black, graphite, metal particles, electronically conductive polymer), the obtained material can be used as an electrochemically active cathode material in lithium batteries.
Examples
Example A
The first solution is prepared by dissolving 0.001 - 0.01 mole of iron (III) acetylacetonate (99.9+ %, Aldrich) in 4.5 - 45 mL JV,iV-dimethylformamide (anhydrous, 99.8 %, Sigma- Aldrich, 227056). Separately, a second solution is prepared of 0.002 - 0.02 mole lithium methoxide (98%, Aldrich, 344370) in 1.2 - 12 mL 2-methoxyethanol (ACS reagent, >99.3 %, Sigma-Aldrich, 360503). Separately, a third solution is prepared from 0.001 - 0.01 mole of titanium (IV) isopropoxide (purum, Fluka, 87560) in 0.6 - 6 mL iV,iV-dimethylformamide
(anhydrous, 99.8 %, Sigma- Aldrich, 227056). The second solution is poured into the first solution and the mixture is thoroughly stirred. The obtained mixture of the first two solutions is poured into the third solution with titanium (IV) ions and the final solution or sol is left to stir for 3 hours. To the obtained solution 0.004 - 0.04 mL of milliQ water purged with argon is added. Simultaneously, 0.0014 - 0.014 mole of ethylene glycol (anhydrous, 99.8 %, Aldrich, 324558) is added. The obtained gel is stored in a closed container and is left in a drying oven at 6O 0 C overnight to completely react, after which it is left standing for approximately 3 days. Then it is dried at 60°C in an open container. The obtained powder is ground in an agate mortar for 10 minutes. Then it is put into an oven and is heated under a CO/CO 2 atmosphere (ratio CO : CO 2 = 1 : 1) at a heating rate of 1 - 20°C/min to 800°C. The obtained product is cooled at a cooling rate 1 — 20°C/min to room temperature after which it is transferred into a drybox with an oxygen and humidity content below 10 ppm. The obtained material is used to prepare the cathode.
Example B
The first solution is prepared by dissolving 0.001 - 0.01 mole of manganese (II) acetylacetonate (99.9+ %, Aldrich, 245763) in 5 - 50 mL λζN-dimethylformamide (anhydrous, 99,8 %, Sigma- Aldrich, 227056). Separately, a second solution is prepared from 0.002 — 0.02 mole of lithium methoxide (98%, Aldrich, 344370) in 1.2 - 12 mL 2-methoxyethanol (ACS reagent, >99.3 %, Sigma-Aldrich, 360503). Separately, a third solution is prepared from 0.001 - 0.01 mole of titanium (IV) isopropoxide (purum, Fluka, 87560) in 0.6 - 6 mL iV,iV-dimethylformamide (anhydrous, 99.8 %, Sigma-Aldrich, 227056). The second solution is poured into the first solution and the mixture is thoroughly stirred. The obtained mixture of the first two solutions is poured into the third solution with titanium (IV) ions and the final solution or sol is left to stir for 3 hours. To the obtained solution 0.004 - 0.04 mL of milliQ water purged with argon is added. Simultaneously, 0.0014 - 0.014 mole of ethylene glycol (anhydrous, 99.8 %, Aldrich, 324558) is added. The obtained gel is stored in a closed container and is left in a drying oven at 60°C overnight to completely react after which it is left standing for approximately 3 days. Then it is dried at 60 0 C in an open container. The obtained powder is ground in an agate mortar for 10 minutes. The continuation is as in Example A, except that the entire process is carried out in an inert atmosphere.
Example C
The first solution is prepared by dissolving 0.001 - 0.01 mole of cobalt (II) acetylacetonate (99.9+ %, Aldrich, 227129) in 5 - 50 mL A^iV-dimethylformamide (anhydrous, 99.8 %, Sigma- Aldrich, 227056). Separately, a second solution is prepared from 0.002 - 0.02 mole of lithium methoxide (98%, Aldrich, 344370) in 1.2 - 12 mL 2-methoxyethanol (ACS reagent, >99.3 %, Sigma-Aldrich, 360503). Separately, a third solution is prepared from 0.001 - 0.01 mole of titanium (IV) isopropoxide (purum, Fluka, 87560) in 0.6 - 6 mL N,iV-dimethylformamide (anhydrous, 99.8 %, Sigma-Aldrich, 227056). The second solution is poured into the first solution and the mixture is thoroughly stirred. The obtained mixture of the first two solutions is poured into the third solution with titanium (IV) ions and the final solution or sol is left to stir for 3 hours. The continuation is as in Example B.
Example D
A solution of 0.002 - 0.02 mole titanium dioxide (titanium (IV) oxide, anatase, Aldrich, 637254) is prepared in 9.7 - 97 mL milliQ water and is dispersed in an ultrasonic bath for approximately 2 hours. To the obtained solution, 0.004 - 0.04 mole of lithium hydroxide is added (reagent grade, >98 %, Aldrich, 442410) and is dispersed for one additional hour. Separately, 0.002 - 0.02 mole of iron citrate (iron (III) citrate hydrate, 98 % Aldrich, 228974) is dissolved in 9.5 - 95 mL of milliQ water at 60 0 C in approximately 1 hour. Both solutions, cooled to room temperature, are mixed and the mixture is dried in a rotary evaporator at 60 0 C until a viscous liquid is obtained that is further dried in a drying oven at 6O 0 C overnight to obtain a powder. The obtained powder is ground in an agate mortar for 10 minutes. Then it is put into an oven and is heated under a CCVCO 2 atmosphere (ratio CO : CO 2 = 1 : 1) at a heating rate of 1 - 20°C/min to 800°C. The obtained product is cooled at a cooling rate of 1 - 20°C/min to room temperature after which it is transferred into a drybox with an oxygen and humidity content below 10 ppm. The obtained material is used to prepare the cathode.
Example E
A solution of 0.002 - 0.02 mole titanium dioxide (titanium (IV) oxide, anatase, Aldrich, 637254) is prepared in 9.7 - 97 mL of milliQ water and is dispersed in an ultrasonic bath for approximately 2 hours. To the obtained solution, 0.004 - 0.04 mole of lithium citrate (lithium citrate hydrate, 99 %, Aldrich, 213209) is added and is dispersed for one additional hour. Separately, 0.002 - 0.02 mole of iron citrate (iron (III) citrate hydrate, 98 % Aldrich, 228974) is
dissolved in 9.5 - 95 niL of milliQ water at 60°C for approximately 1 hour. Both solutions, cooled to room temperature, are mixed and the mixture is dried in a rotary evaporator at 6O 0 C until a viscous liquid is obtained that is further dried in a drying oven at 6O 0 C overnight to obtain a powder. The continuation is as in Example D.
Example F
A solution of 0.002 - 0.02 mole titanium dioxide (titanium (IV) oxide, anatase, Aldrich, 637254) is prepared in 9.7 - 97 mL of milliQ water and is dispersed in an ultrasonic bath for approximately 2 hours. To the obtained solution, 0.002 - 0.02 mole of citric acid (99 %, Aldrich, C83155) is added and is dispersed for one additional hour. To the obtained solution 0.004 - 0.04 mole of lithium acetate (lithium acetate dihydrate, 99 %, Fluka, 62393) is added and the dispersing is continued for 30 minutes. Separately, 0.002 - 0.02 mole of manganese (II) acetate tetrahydrate (purum p. a., Aldrich, 63537) is dissolved in 9.5 - 95 mL of milliQ. Both solutions, cooled to room temperature, are mixed and the mixture is dried in a rotary evaporator at 6O 0 C until a viscous liquid is obtained that is further dried in a drying oven at 8O 0 C under vacuum overnight to obtain a powder. The continuation is as in Example D, except that heating is done under an argon atmosphere.