WO1999000326A1

WO1999000326A1 - Method of preparing metal and mixed metal oxides

Info

Publication number: WO1999000326A1
Application number: PCT/US1998/013366
Authority: WO
Inventors: Sunity K. Sharma; Subhash C. Narang; Kuldip K. Bhasin; Susanna Ventura
Original assignee: SRI International Inc; Stanford Research Institute
Current assignee: SRI International Inc
Priority date: 1997-06-26
Filing date: 1998-06-25
Publication date: 1999-01-07
Anticipated expiration: 1999-12-26
Also published as: AU8172598A

Abstract

Metal and mixed metal oxides are prepared using a redox reaction among components mixed at an atomic level in solution, and irradiating the solution with an appropriate energy source. In one aspect of preferred embodiments, the redox reaction is initiated using microwave energy directed at the solution. In another aspect of preferred embodiments, the metal precursor salt provides an oxidizing ligand. In yet another aspect of preferred embodiments, the solution is aqueous.

Description

METHOD OF PREPARING METAL AND MIXED METAL OXIDES

Techical Field The field of the invention is metal oxides.

Background of the Invention

Metal oxides have physical, chemical, electrical, magnetic, optical and other characteristics providing utility in many different applications. Among other things, metal oxides have been found to be useful as protective coatings, pigments, catalysts, electrode materials, conductors, insulators, inclusion materials such as grits and non-slip agents, ceramics, and electrochromic applications.

Mixed metal oxides are defined herein to be a subset of metal oxides in which different metals are bound together with oxygen in the same molecule. The definition includes compounds having the general formula, M'_x! . . . Mⁿ _xnO_y, where M'_xι . . . Mⁿ _n represents n different metals, and the various metal and oxygen species are present in relative atomic ratios given by xl . . . xn and y, respectively. The definition also includes M'_xι . . . Mⁿ _xnO_y compounds that are "doped" by inclusion of other non-homogeneously distributed chemical species, such as metal, ceramic or other particulates, as well as the hydroxide and hydrated forms of such compounds. The definition of mixed metal oxides used herein does not, however, include compositions in which individual mono-metallic metal oxides are merely present as a solid-solid or other mixture, rather than being chemically bonded together. The definition also does not extend to compounds such as metal alkoxides and alkanolamines.

Mixed metal oxides are of particular interest in many of the applications listed above because the presence of different metals often imparts special properties to the compound. Barium Titanate (BaTiO₃), for example, is widely used in capacitors, transducers, thermistors and so forth, Yttrium Barium Copper Oxide (YBa₂Cu₃O_x) and other mixed valent spinels have been investigated as superconductors, and lithium niobium oxides (LiNbO₃) have been investigated as ferro-electric materials. Metal oxide electrodes are also particularly advantageous in the production of secondary battery electrodes, where the life and energy efficiency of secondary batteries depend to a great extent upon the morphology and composition of the electrodes, and one class of such metal oxides, the lithiated metal oxides, LiM^pιM^qn...O_x, (including, for example, LiAl₀₂Mnι_.8Ox, LiCo0₂, and LiMn₂O₄) are increasingly used in the so-called re-chargeable rocking chair batteries. In such devices the metal oxides act as cathode materials by reversibly intercalating and deintercalating lithium during repetitive discharging and charging.

Despite a significant interest in mixed metal oxides, the synthesis of metal oxides is often accompanied by operational difficulties. Mixed metal oxides are conventionally prepared by combining pre-formed mono-metallic oxides, such as in sol-gel¹, high temperature sintering^2"4, co-precipitation⁵ or Pechini⁶ processes. There are, however, significant problems with all of these conventional methods. In sol-gel and co-precipitation processes, for example, the constituting components of the mixed metal oxides tend to be inhomogeneously mixed during production. This results in the separation of microphase materials. Similarly, prolonged sintering at high temperatures is problematic because it is inefficient and the diffusion reactions may still not go to completion. Still further, where non-aqueous systems are used, as for example in Pechini process, the poor solubility of the metal salts drastically reduces the ceramic yield of the reaction mixture due to a very high concentration of organics.

It is also known to prepare mixed metal oxides using metal oxide precursors. For example, it is known to coat a substrate with a slurry containing a mixture of mono-metallic metal oxide precursors, dry the slurry, and then react the precursors with an oxidizing or reducing agent in gaseous form (O₂ or H₂). Such methods are time consuming, however, do not necessarily produce homogeneous mixed metal compositions, and are limited primarily to preparing surface coatings.

EP 0 366 313 Bl to Kourtakis (Sep. 1993) discloses a process in which mixed metal oxides are formed from an aqueous solution of monometallic metal precursor salts, in which at least one of the monometallic salts is a nitrate, and another of the salts carries a reducing ligand, such as a formate, acetate or proprionate. The mixture is spray dried, and heated to 400°C to initiate a redox reaction. Finaly, the product is heated to 900°C.

US Pat. No. 5,728,362 to Greunter et al., (March, 1998) teaches an improvement to the EP process in which either the oxidizing or reducing agent may be provided by a source other than one of the metal precursor salts. In a preferred example, the Greunter patent teaches a solution in which the oxidizing agent is provided by the nitrate of a metal nitrate, and the reducing agent is provided by an acid solvent. The process, however, still contemplates drying the solution to a powder, and then subsequently initiating the redox reaction within the dried powder.

Both the Kourtakis and Greunter processes are still undesirable in that they require spray drying apparatus, and in that they introduce inhomogeneities by initiating the redox reaction among components disposed in a solid phase.

Thus, there remains a need for new methods in the production of mixed metal oxides.

Summary of the Invention

The present invention is directed to methods and apparatus in which a mixed metal oxide is prepared using a redox reaction which takes place in solution, wherein at least one of the oxidizing and reducing agents of the redox couple is derived from a metal precursor salt.

In one aspect of preferred embodiments, the redox reaction is initiated using microwave energy directed at the solution. In another aspect of preferred embodiments, the metal precursor salt provides an oxidizing ligand. In yet another aspect of preferred embodiments, the solution is aqueous.

Brief Description of the Drawing

Figure 1 is a flowchart of steps in a process according to the present invention.

Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention.

Detailed Description

Figure 1 depicts steps in a process according to the present invention. In step 10, a plurality of metal salts is placed into a solution using an appropriate solvent. Each of the salts have a ligand which is either an oxidizing agent or a reducing agent, and which forms part of a redox system. In step 20, an oxiding or reducing agent is added to the solution, which agent forms another part of the redox system. In step 30, sufficient energy is imparted to the solution to initiate a reaction between or among the agents of the redox system, and thereby produce a mixed metal oxide. In step 40, the solvent is removed, and in step 50 the mixed metal oxide is ground or otherwise subjected to further processing.

Turning in further detail to step 10, almost any metal can be utilized as part of a contemplated salt. The chief requirements are that the salt can be solvated in an appropriate solvent, and further that the metal is capable of forming an oxide. Appropriate metals specifically include the alkali metals, alkaline earth metals and transition metals, and their presence or absence will largely be application dependent. For example, metals such as Lithium, Manganese, Cobalt, Nickel, are particularly well suited for battery applications, while Barium, Titanium, and Lead are particularly well suited for piezoelectric applications. It is further contemplated that the various salts may or may not be mono-metallic salts. Salts having two, three, four or even more different metals are specifically contemplated. Thus, salts employed in step 10 may include multi-metallic salts including LiAl₀₂Mnι ₈Ox, LiCo0₂, and LiMn₂O .

Taken altogether, the metals in the various salts will advantageously be present in stoichiometrically appropriate concentrations which result in the desired mixed metal oxide. Thus, it is contemplated that since mixed metal oxides according to the teachings herein may include metals in either equal or unequal atomic concentrations, and the concentrations of the respective salts may range anywhere from exact equivalence to merely doped quantities.

The metals in the various salts may be complexed with their respective ligands in many different ways. Thus, the metallic-ligand bonds may be more or less of an ionic nature, although complexes having bonds of relatively more ionic character are preferred because they generally result in increased solubility. Metal nitrates and nitrites, for example, are both contemplated, as are acetates, nitrates, formates, citrates, oxalates, etc. Of course, the ligand has a great deal to do with the solubility of the salt. Thus, while essentially all sodium and potassium salts are soluble in water, most silver salts are insoluble, and transition metal salts may or may not be soluble unless the ligand assists solubility. Acetates except silver, mercury and bismuth are generally soluble, nitrates are almost always soluble, while sulfates are only usually soluble. Carbonates, sulfides and nitrides are generally disfavored because they tend to be insoluble

It is also highly advantageous that the ligands forming part of the metal salts also form part of a redox system which produces a gaseous end product, thereby removing the ligands from the solution. From this perspective, the nitrates and nitrites are especially preferred.

Other components can be added to the solution as well, and such additional components may or may not chemically react with the other ingredients. Examples of contemplated additional components are suspended ceramic or metal particles. Such included materials may be advantageously added to modify characteristics of the mixed metal oxide. For example, carbon black can be added to enhance electrical conductivity, and iron powders can be added to enhance ferro-magnetic properties. In other examples, materials may be added which enhance brittleness, compression strength, or elasticity. A viscosity modifier such as PEO or PEG may also be added. Where such additional components are added to the solution and become integrated into the mixed metal oxide, the mixed metal oxide is still considered herein to have the nominal formula M'_xι . . . Mⁿ _xnO.

Sometimes it is desirable to have metal oxides as composites with carbon. This can be achieved by physically mixing a metal oxide with carbon which may be graphitic, soot or other allotropic form. The mixing operation may be performed by grinding, for example in a ball mill. However, a better mixing may be achieved by pyrolysing the metal salts of organic acids in absence of oxygen. A few organic compounds are known to generate specific allotropic forms of carbon, for example, 3,4,9,10 - perylenetetracarboxylic acid is a precursor to graphitic carbon. By reacting this tetra basic acid with metal ions in different proportions and pyrolysing the resulting metal compound in argon or nitrogen, metal oxide composites having different amounts of graphite to metal oxide may be obtained. Working Example 8 detailed below exemplifies the formation of TiO₂ as a composite with graphite.

The solvent employed in step 10 is contemplated to be any suitable solvent, provided that the solvent is capable of solvating the salts. Water is a presently preferred solvent, both because of its superior solvating ability, and because it is inexpensive and non-hazardous. Nitrates, for example, are almost always soluble in aqueous solutions. On the other hand, it is contemplated that non-aqueous solvent can be employed, such as various organic solvents. Preferred organic solvents include alcohols, dimethyl sulphoxide, ethyl acetate, and formamide. Such organic solvents may be particularly useful for solvating transition and non-transition metal ions. Still further, mixed solvents may be advantageously employed, such as mixtures of water with alcohols, dimethyl sulphoxide, ethyl acetate, and formamide. Mixed solvents may be particularly useful for solvating metal organics, including metal carboxylates and transition metal, and non-transition metal complexes having organic ligands.

In addition to stoichiometric concerns, it is contemplated that the absolute concentrations of the various components in the solvent will be appropriate for the intended reaction. For example, the metal salts may advantageously have an initial concentration of between about 1% w/w and 25% w/w, and separately added reducing or oxidizing agent may advantageously have an initial concentration falling between about 5% w/w and 90% w/w. Higher concentrations are problematic in that the redox reaction is disfavored where grossly non-equivalent amounts of reducing and oxidizing agents are present. Lower concentrations are also problematic in that the reaction tends to proceed too slowly, and unnecessary steps and energy may be required to remove excess of the non-equivalent amount.

Any suitable vessel may be employed to contain the salt solution. Considerations include suitable venting if it is desired to permit the solvent to volatilize, and sufficient radiative surface area, jacketing or other means for removing excess heat form the system. Obviously, the vessel must also be capable of handling the volumes contemplated to be processed. In this regard it is contemplated that both batch and continuous processes are contemplated. Suitable vessels for continuous processing, for example, may comprise a rotary furnace having an internal lining which is not easily corroded. It is still further contemplated that suitable vessels will be adapted to receive or permit passage of the activation energy to initiate the redox system. Thus, where microwaves are employed as the energy source, at least some portion of the vessel must be capable of passing the microwaves. In such cases, solvents capable of absorbing microwave energy, such as chlorobenzene, may also be used.

In step 20, it is contemplated that the oxiding or reducing agent will be selected to cooperate with the ligand(s) from the metal salts to form a suitable redox system. Preferred redox systems are those which have an appropriate activation energy, usually at about 220 °C to about 550 °C, and that react substantially to completion under the reaction conditions without reacting too violently. Thus, for example, some redox systems would be explosive under the expected conditions, and are therefore highly disfavored. Other disfavored redox systems may not be explosive, but are still so reactive that excess heat production is problematic. Preferred redox systems are also those which generate a gaseous or liquid product which is readily removed from the solution. To this end redox systems are preferred that produce a gas, such as NOx, SOx, COx, N₂ and N O, or that produce water, alcohol or other readily evaporated substance.

In many instances the redox system will comprise a simple redox couple, such as nitrate and acetate. While it is possible that one or more of the metal salts will have a reducing ligand, and the oxidizing agent will be provided separately, it is preferred that at least one of the metal salts will have an oxidizing ligand, and that the reducing agent will be separately added to the solution. Preferred reducing agents for this purpose are organic acids, including non-polymerizing carboxylic acids such as formic acid, citric acid, and ascorbic acids. Polymerizing organic acids such as methacrylic, acrylic, crotonic acid, etc. may also be used, although such acids may combine to produce a product which is difficult to separate from the mixed metal oxide product.

In an exemplary class of embodiments, mixed metal oxides of the form M^pιM^qnM^rπι ...0(p/2+q+3r/2) can be produced by heating an aqueous mixture of metal nitrates and carboxylic acids at low temperature. The formation of the metal oxide under these conditions is thought to be facilitated by spontaneous reaction between the oxidizing N0₃-/N0₂ and the organic ligands such as acrylate, methacrylate, formate, citrate, acetate, ascorbate, picolinate, salicylate, etc. A significant advantage of a nitrate-carboxylate system is the ability of these systems to undergo pyrolysis in an ordinary household microwave oven to give the ceramic, which may then be sintered to get the final product. Working Example 4 (detailed below) illustrates the use of a microwave oven to obtain a desired ceramic.

In more complex redox systems, there can be combinations of oxidizing and/or reducing agents. Combinations of acids, for example, can be used as reducing agents. Contemplated examples of complex redox systems include tartaric acid and ascorbic acid. It is also contemplated that the various salts themselves may provide both oxidizing and reducing agents. The EP 0 366 313 B1 application to Kourtakis discussed above, for example, discloses metallic precursor salts, in which at least one of the salts carries an oxidizing nitrate, and another of the salts carries a reducing ligand, such as a formate, acetate or proprionate.

Just as the metals in the metal salts are preferably included in stoichiometric proportions to produce the intended mixed metal oxide, the various ligands employed in the redox system are preferably included in stoichiometric proportions to react completely with each other.

In step 30, the activation energy required to initiate reaction in the redox system can be provided by any suitable energy source. In our experiments reacting small quantities of materials, we have been most successful using microwave energy for this purpose. In such experiments the solution has generally been contained within a glass petri dish, and the microwaves have been provided using a common household microwave having a rated capacity of 1100 watts. We have also had good results using radiative or convective heat, such as that produced by a hot plate. Still further, other energy sources such as ultraviolet light, CO₂ laser, diode laser, infra red lamp, solar energy, and electric current are contemplated.

The amount and intensity of the activating energy is preferably also a function of other reaction conditions. Under the concentrations discussed above, microwave energy for about 10 minutes is generally sufficient to initiate many redox systems, during and after which the reaction is self perpetuating due to the exothermic nature of the reaction.

Following initiation of the redox system, the temperature of the mixture during processing can fall anywhere between about 50 °C and about 500 °C, and may vary or remain constant during processing. It is further contemplated that the reaction time will fall within the several hours to several days range. Stirring or other mixing is clearly advantageous during the reaction to increase homogeneity of the final product, but there are wide limits on such mixing. In some cases, especially when polymerizing acids are used it may be advantageous to age the contents for a short period ranging from an hour to several hours. However, over-aging may be avoided to preclude the possibility of phase separation. In step 40, the solvent can be separated from the mixed metal oxide product in several different ways. In preferred embodiments the redox reaction is carried out until a substantial increase in viscosity is attained, during which time the solvent is largely evaporated from the reacting mixture. In other embodiments, the solvent can be removed by filtration. In some instances, removal of the remaining solvent may be augmented by addition of an azeotropic substance. It is also contemplated that solvent can be removed using microwave radiation.

Depending on reaction conditions, the methods disclosed herein can be used to prepare any combination of amorphous, crystalline pure and mixed metal oxide powders. For production of amorphous products it is advantageous that no sintering is carried out subsequent to microwaving. For production of crystalline pure products it is advantageous that prolonged sintering at 500°C to 900°C is carried out for one to several hours.

Among the many advantages of the present methodology is that one can achieve mixing of the various metal oxides on an atomic level. Moreover, atomic level mixing can be achieved relatively simply, and at relatively low temperature and moderate reaction conditions. It therefore will not generally be necessary, for example, to further process the mixed metal oxides by repeated grinding and calcination, or subjecting the oxides to temperatures above about 500 °C.

Nevertheless, in step 50 it is contemplated that mixed metal oxide products can be further processed into flakes, pellets, and other morphologies. In one contemplated method of producing flakes, the metal oxide is taken along with a polymer (such as polymethyl methacylate) in a solvent (such as chloroform) compatible with the polymer, and then sprayed onto a substrate using an air brush or an ultrasonic sprayer. Alternatively, the polymer/metal oxide may be coated onto a substrate using a doctor blade or dip coater. In any event, the substrate may advantageously be pretreated with a surfactant which does not leave a residue. This treatment of the substrate assists in dislodging the flaky ceramic from the substrate. It may also be advantageous to employ a highly flexible substrate to assist in dislodging the flakes. Plastic substrates such as Kapton™, Kevlar™, and Teflon™ may be used for this purpose. After application, the solvent may be removed by warming as necessary, and the flakes of the material may then be readily dislodged from the substrate and sintered. A specific example of this process is given in Working Example 3, (detailed below). In other embodiments it is contemplated to provide a surface treatment to the substrate which modifies adhesiveness of the metal oxide.

It is not absolutely necessary to always use a metal acrylate, especially due to the lower solubility of metal acrylates in water. In such circumstances a solution of metal nitrates and acrylic acid in aqueous or mixed aqueous solutions may be microwaved to get the metal oxide. The following example further illustrates this concept.

Mixed metal oxide products prepared as disclosed herein may also be further processed by extrusion, spun into fibers, or deposited as films. It is also contemplated that mixed metal oxide products can be further processed during the solvent removal stage, such as by various forms of atomizing, electro-spraying, and thermal spraying. In short, it is contemplated that mixed metal oxide products prepared as disclosed herein may be processed in any manner in which metal oxide products in general may be processed.

In many instances it will be helpful to sinter the mixed metal oxide during step 50. Working Example 5 (detailed below) illustrates this concept.

Experiments

In our experimental work, we have successfully achieved the syntheses of mixed metal oxides containing more than two metals by taking an aqueous mixture of the metal nitrates and acrylic acid followed by low temperature pyrolysis to yield the metal oxide free from organics. The relative amounts of the metal nitrates and the unsaturated carboxylic acids can be adjusted to effect a complete oxidation of the organics at low temperature. A short sintering session may be required to improve the crystallinity. The method has been successfully used to prepare doped and undoped metal oxides of the type, LiAl_0.2Mni.₈0_x, LiCoO₂, LiMn₂O₄, etc.

Example 1 In a particular experiment, 7.54 gm lithium nitrate, 54.95 gm manganese(II) nitrate tetrahydrate and 40 gm acrylic acid were combined in 80 ml of water and stirred overnight to let the viscosity of the solution increase due to partial polymerization. This solution is burnt at 300- 400 °C to yield a partially sintered material with reasonable crystallinity. A final sintering at 800 °C for 2 hours gives a highly crystalline material as seen by its x-ray diffractogram (not shown).

Example 2

As a particular example of a doped mixed metal oxide, we prepared the aluminum doped lithium manganese oxide, LiAl₀₂Mni_.g0_x by taking a mixture of the respective metal nitrates and acrylic acid in water, followed by low temperature pyrolysis and then short sintering at high temperature. Similar procedures can be used to dope a wide range of metal oxides, for example, LiMn₂O₄, with dopants from the metals of groups IB, IIB, IIIA&B, IVA&B, VA&B, VIA&B, VIIA and VIII and the lanthanides and the actinides.

Example 3

1.8 gm of polymethylmethacrylate PMMA) was taken along with 10.2 gm of lithium cobalt oxide in about 50 ml chloroform. The contents were stirred to allow PMMA to dissolve. 0.2gm of KD1 surfactant dissolved in about 25 ml chloroform was sprayed on one side of a 30cm x 40cm sheet of Kapton, 0.05 mm thick. Following this surface treatment, the slurry of LiCoO₂ prepared above was air sprayed on to it to get a coating of 0.08 - 0.1 mm thickness. This coated Kapton sheet was dried in an oven at HOC for about 1 hour. LiCoO₂ was removed as (green) flakes by a scraper. The green flakes were sintered in air at 920C for 16 hours to get the ceramic flakes.

Example 4 0.79 gm of lithium acrylate and 5.16 gm of Mn(NO )₂ 4.4 H₂O were taken in about 8 ml of water in a 50 ml beaker. The contents of the beaker were agitated and heated to 40 - 45C for 10 minutes. The resulting solution had minor suspension in it and was not removed. About one ml of the solution was placed in a pyrex petri dish and the dish was placed in a house hold microwave (Sharp, Carousel, 1100 watt, 1.3 cubic feet). The contents were microwaved at full power for 5 minutes. This lead to scintillations and "burning' of the contents and the formation of the metal oxide.

Example 5

0.82 gm of lithium acrylate and 5.25 gm of Mn(NO₃)₂ 4.4H₂O were taken in a 50 ml beaker along with about 10 ml of water. The contents of the beaker were agitated and warmed to about 40C for 10 minutes. A few drops of the resulting transluscent solution was placed on a 1" x 1" Kapton piece. This was then microwaved a full power for about 1 minute in a house hold microwave (Sharp, Carousel, 1100 watt, 1.3 cubic feet). The solution "burnt" leading to a fluffy mass. The fluffy mass was gently brushed by a soft camel hail brush leaving a film of the metal oxide on Kapton.

Example 6

In a 400 ml glass beaker 46.46 gm of Mn(NO₃)₂ 4.4H₂O was dissolved in about 90 ml of water. To this solution was added 21.60 gm of acrylic acid. The contents were agitated for about 1 hour. 6.89 gm of anhydrous lithium nitrate was added to this solution and agitated to dissolve. 7.50 gm of Al(NO )₃ were dissolved in the above mixture of metal nitrates and acrylic acid. The contents were stirred for 14 hours at room temperature to get a solution. About 7 ml of this solution was microwaved as exemplified in Example 2 above. Micro waving lead to burning and subsequent production of the metal oxide.

The formation of metal oxides by this method can be extended to other alkali metals, transition and non-transition metals as well. Another example of a transition metal oxide is that using cobalt(II) nitrate as described in Working Example 7 below.

Example 7

3.44 gm of powdered lithium nitrate 14.54 gm of cobalt(II) nitrate hexahydrate were taken with about 25 ml water in a 100 ml beaker. The contents of the beaker were stirred for about 1/2 hour and an additional about 5 ml water was added and stirring continued for another 1/2 hour. About 6 gm of acrylic acid were added to this solution followed by stirring for another about 15 minutes. 5 ml of this solution were microwaved as detailed in Example 2 above which lead to scintillations and burning of the reactants leading to the formation of metal oxides.

Example 8

In about 6 ml of acetonitrile was taken 0.85 gm of 3,4,9, 10-perylene tetracarboxylic acid and 0.28 gm of titanium(IV) isopropoxide in a 50 ml round flask fitted with a reflux condenser. The contents of the flask were refluxed for about 2 hours in an oil bath kept around 80 - lOOC. Heating was then discontinued and the reaction flask allowed to come to room temperature. Acetonitrile was removed by vacuum and the resulting solid was pyrolysed in argon at 800C for

Applications

The methods are applicable to production of a wide range of doped or undoped electrodes, and can also be used in the synthesis of super conductors, semiconductors, piezeoelectric materials, etc.

Thus, specific embodiments and applications of methods for preparing mixed metal oxides have been disclosed. It should be apparent, however, to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. For example, initiation energy of the redox reaction could take place using a diode laser for continuous production of films. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims.

References: 1. P. Barboux, J.M. Tarascon and F.K. Shokoohi, J. Solid State Chemistry, 94, 185 (1991)

2. Y. Gao and J.R. Dahn. 3 Electrochem Soc, 143, 1783 (1996)

3. M.M. Thackeray. J. Electrochemical Soc proceedings, 94, 233 (1994)

4. T Ohzuku, A. Ueda and N. Yamamoto, J. Electrchem. Soc. 142, 1431(1995) 5. J.A.Voigt, T.J.Boyle, D.H.Doughty, B.A.Jiernandez, B.J.Johnson, S.C.Levy,

C.J.Tafoya and M.Rosay, Mat. Res. Soc. Symp. Proceedings 393, 101(1995) 6. M.P Pechini, U.S. Patent 3,330,697 (1967)

Claims

CLAIMSWe claim:

1. A method of synthesizing a metal oxide comprising: providing a liquid solvent; introducing a plurality of metal salts into the solvent to form a solution, the solution comprising at least one oxidizing agent and at least one reducing agent, where at least one of the oxidizing and reducing agents is derived from at least one of the metal salts; initiating a redox reaction in the solution between the at least one oxidizing agent and the at least one reducing agent; and deriving the metal oxide from the solution.

2. The method of claim 1 wherein the at least one oxidizing agent is complexed with at least one of the metal salts.

3. The method of claim 2 wherein the at least one oxidizing agent is selected from the group consisting of a nitrate, a nitrite, and a perchlorate.

4. The method of claim 1 wherein the at least one reducing agent is complexed with at least one of the metal salts.

5. The method of claim 4 wherein the at least one reducing agent comprises an organic acid.

6. The method of claim 5 wherein the at least one reducing agent is selected from the group consisting of acrylate, methacrylate, formate, citrate, acetate, ascorbate, picolinate, and salicylate.

7. The method of claim 1 wherein the at least one oxidizing agent is complexed with at least one of the metal salts, and wherein the at least one reducing agent is complexed with at least another one of the metal salts.

8. The methods of any of claims 1 - 7 wherein the redox reaction is initiated using microwave energy.

9. The methods of any of claims 1 - 7 wherein the solution is aqueous.

10. The methods of any of claims 1 - 7 wherein the solution is non-aqueous.

11. The methods of any of claims 1 - 7 wherein the solution is mixed aqueous/non- aqueous.

12. The methods of any of claims 1 - 7 wherein the metal oxide has a nominal composition, M'_xι . . . M^Oy, where M'_xι . . . Mⁿ _n2 represents n different metals, and the various metal and oxygen species are present in relative atomic ratios given by xl . . . xn and y, respectively, and n > 2.

13. The method of claim 11 wherein n = 2.

14. The method of claim 11 wherein n = 3.

15. The method of claim 11 wherein n = 4.

16. The method of any of claims 1 -7 wherein the metal oxide comprises Lithium.

17. The method of any of claims 1 -7 wherein the metal oxide nominally comprises Lithium and a transition metal.

18. The method of any of claims 1 -7 wherein the metal oxide nominally comprises Lithium, a first transition metal, and a second transition metal.

19. The method of any of claims 1 -7 wherein the metal oxide nominally comprises and a transition metal and a non-transition metal.

20. The method of any of claims 1 -7 wherein the metal oxide nominally comprises a first non-transition metal and a second non-transition metal.

21. The method of any of claims 1 -7 further comprising forming the metal oxide as a carbon composite film on a plastic substrate using microwave energy.

22. The method of any of claims 1 -7 further comprising forming the metal oxide as a carbon composite film having multiple metal species on a plastic substrate using microwave energy.

AMENDED CLAIMS

[received by the International Bureau on 17 November 1998 (17.11.98); original claims 1 and 3 amended; remaining claims unchanged (1 page)

1. A method of synthesizing a metal oxide comprising: providing a liquid solvent; introducing a plurality of metal salts into the solvent to form a solution, the solution comprising a redox couple having at least one strong oxidizing agent and at least one strong reducing agent, wherein at least one of the oxidizing and reducing agents is derived from at least one of the metal salts: initiating a redox reaction in the solution between the at least one oxidizing agent and the at least one reducing agent, said initiating step occurring while the solution is supported by a non-gaseous substance: and deriving the metal oxide by establishing the redox couple.

3. The method of claim 2 wherein the at least one oxidizing agent is selected from the group consisting of a nitrate, a nitrite, perchlorate, and a persulphate.

9. The methods of any of claims 1 - 7 wherein the solution is aqueous.

10. The methods of any of claims 1 - 7 wherein the solution is non-aqueous.