EP0843648A1

EP0843648A1 - Synthesis of lithiated transition metal oxides

Info

Publication number: EP0843648A1
Application number: EP96946139A
Authority: EP
Inventors: Jack Wolstenholme; Wu Li; John C. Currie; Maurice Dubois
Original assignee: Nv Union Miniere Sa; Union Miniere NV SA
Current assignee: Nv Union Miniere Sa; Umicore NV SA
Priority date: 1995-08-02
Filing date: 1996-07-23
Publication date: 1998-05-27
Also published as: KR19990036085A; CN1192193A; WO1997005062A1; JPH11510467A; AU6410696A; CA2227534A1

Abstract

A synthesis for lithiated transition metal oxide powders is provided which comprises reacting one or more transition metal compounds with a lithium compound, wherein the lithium compound is in a molten phase. The reaction mixture may contain additives, which act primarily to extend the temperature range of the molten phase of the lithium compound.

Description

SYNTHESIS OF LITHIATED TRANSITION METAL OXIDES

Field of the Invention

The invention relates to a process for the synthesis of lithiated transition metal oxides, from lithium compounds and one or more transition metal oxides, or compounds which decompose to transition metal oxides, or react directly with the lithium compounds, under the reaction conditions. The produced lithiated transition metal oxides or lithiated mixed transition metal oxides are suitable for use as a cathodic material in lithium ion battery systems. Background of the Invention

Lithiated transition metal oxide powders, such as the most commercially used lithium cobalt dioxide, LiCoθ2, are utilized as cathode materials for the positive electrode in rechargeable lithium ion batteries. Lower cost materials, such as lithium nickel dioxide and lithium manganese dioxide, would be preferred, but have proven particularly laborious to make, because utilizing prior art processes for their preparation involves multiple grinding steps and calcination stages.

Specific chemical, morphological and physical characteristics are required to sustain the desired electrical properties of the lithiated transition metal oxide powder over the many hundreds of sequential charge and discharge cycles demanded during service. Current battery applications for powders demand high purity (>99%), homogeneity (of the lithiated structure), controlled particle sizes (usually within the range of 1 to 25 microns) and specific surface areas (usually within the range 0.1 to 5 m²/g). Lithium transition metal oxides are usually made by variations on a standard route, namely the solid state reaction of a preblended mixture of lithium oxide and the transition metal(II) oxide, in a current of air or oxygen, at temperatures ranging from about 400° to 900°C. The lithium oxide is generated in-situ during the calcination, by the decomposition of a lithium compound, usually the carbonate or hydroxide. It is also well known to use other lithium compounds, exemplary of which is the nitrate. The transition metal(II) oxide is also usually generated in-situ during the calcination, by the decomposition of a transition metal(II) compound. For the synthesis of lithium cobalt dioxide, the transition metal(II) compound is usually cobalt(II) carbonate, although the nitrate and hydroxide have also been utilized.

It is known that good mixing of the powders, prior to calcination, accelerates formation of the product as does increasing the calcination temperature. However, temperature also determines the structure of the product. For example, in the case of lithium cobalt dioxide synthesized at calcination temperatures as low as 400°C, lithium cobalt oxide having a spinel structure is formed, which exhibits somewhat different properties to the desired, layered, "rock salt" structure produced at 900°C.

Typically, in these prior art methods, as described for example in U.S. patent 4,302,518 to J.B Goodenough et al., the reaction mixture is preblended, usually by grinding with a mortar and pestle or in a ball mill, and the powder may be optionally compacted, before being introduced into the furnace. After a predetermined calcination time period, the product is removed from the furnace, reground and may be compacted again before being calcined for one or more additional time periods to ensure complete conversion to lithium cobaltic dioxide. The final grinding produces the desired grain sized powder for use in the battery cathode.

During recent years the emphasis of research work has shifted away from the preparation of the lithium cobalt dioxide powder per se and toward the production of lithiated transition metal compounds requiring less costly, but equally effective, transition metals.

The patent literature provides many examples of other novel lithium ion systems and variations on the methods for the preparation thereof. In U.S. patent 5,160,712 issued to M.M Thackeray et al., there are disclosed lithium transition metal oxides and methods for their preparation. The method comprises admixing the reactants, prior to heating the mixture to a temperature of 400°C, and for a period of time sufficient to form an essentially layered lithium transitions metal oxide structure (which includes certain spinel type structures), wherein at least part of the heating is conducted under a suitable oxygen containing atmosphere.

Similarly, U.S. Patent 4,980,080 to A. Lecerf et al describes a process for the preparation of a material suitable for use as a cathode in an electrochemical cell wherein the starting materials are a mixture of hydrated lithium hydroxide and nickel or cobalt oxide which are heated in air at temperatures ranging between 600° to 800°C. A two-stage reactant mixing and reheating operation is utilized to thereby accelerate the process.

As a further example, the hydrides of lithiated nickel dioxide and the secondary cells prepared therefrom are disclosed in U.S patent 5,180,574 issued to U. Von Sacken. The compounds are prepared using nickel oxides, nickel hydroxide, and mixtures thereof, which are reacted with about a twenty five percent excess of lithium hydroxide, at about 600°C in an atmosphere having a partial pressure of water vapour greater than two torr.

Despite the number and diversity of these prior art processes, nevertheless, there has not been developed a satisfactory method of controlling the physical characteristics, such as particle size and surface area, of lithium cobalt dioxide powder and other lithium transition metal powders. Further, commercially viable processes, deleteriously, require multiple calcination steps. It has also been found that the prior art processes do not scale up easily without significant adjustments to the procedures. Summary of the Invention

It is a primary objective of the present invention to provide a selection of lithium transition metal oxide powders having specific particle size and size distribution and controlled microstructure for use in lithium ion battery systems.

It is a further objective to provide a single stage synthetic route for the production of lithiated transition metal oxide powders.

In accordance with the present invention, there is provided a process for the synthesis of lithium transition metal oxide powders having predetermined particle size and controlled microstructure which comprises: reacting one or more transition metal compounds with a salt, oxide or hydroxide of lithium, said lithium compound being in a molten phase, and optionally, an additive which is functional to increase the effective molten phase temperature range of said lithium compound, in an atmosphere functional to control the thermal decomposition of said lithium compound and to maintain, or convert and maintain, the transition metal compound in an oxidation state which corresponds to the oxidation state of the transition metal in the product, at a temperature and for a time effective to thereby form the desired lithium transition metal oxide.

Suitable lithium compounds would be selected from the salts, oxides or hydroxides of lithium.

The transition metal compounds would be selected from the oxides of cobalt, nickel, manganese, vanadium, iron, titanium or chromium, or mixtures thereof. Preferably, the transition metal compounds would be selected from the oxides of cobalt, nickel or manganese or mixtures thereof. Alternatively, suitable transition metal compounds would be selected from the hydroxides, carbonates or salts of cobalt, nickel, manganese, vanadium or chromium or mixtures thereof.

The additives, which may be utilized optionally, are believed to promote formation of the liquid phase and extend the temperature range of the molten phase of the lithium compound. The most effective additives have been found to be alkali metal compounds, particularly potassium or sodium hydroxide or mixtures thereof, which have very wide ranging molten temperatures extending from 300 to above 1200°C. The preferred additive is potassium hydroxide.

The reaction must be undertaken in an atmosphere which is functional to either convert the transition metal compound to an oxide and/or to maintain the transition metal oxide in the correct oxidation state namely the same oxidation state as the transition metal in the final product. Thus, the reaction atmosphere may comprise an inert atmosphere, a reducing atmosphere or an oxidizing atmosphere depending upon the nature of the reactants.

As will be evident to one skilled in the art, it is possible to produce the lithium transition metal oxide powders of predetermined particle size and controlled microstructure by controlling reaction time and temperature during the heating stage. The temperature ranges would extend from 200°C to 1200°C and the residence times from lh to 72h. The elevated temperature controls the structure and is necessary for the reaction to take place, whereas the residence times determine the resultant particle size and surface area. The desired structure defines the reaction temperature and at this temperature the lithium compound and/or additive must be optimized whereby the lithium compound and molten medium provide the desired environment for growing the particles with the desired microstructure.

The reaction mechanism postulated for the synthesis of lithium transition metal oxides was extrapolated from the discovery, that in the synthesis of lithium cobaltic dioxide from cobalt (III) oxide and an excess of lithium carbonate, the lithium carbonate is retained in the molten state during the reaction. The reaction takes place above 720°C and in a static, neutral or non-oxidizing atmosphere, with the lithium carbonate undergoing partial decomposition to form carbon dioxide which is retained in the static atmosphere. The reaction thus occurs in the molten state, under optimum thermodynamic conditions. Without being bound by same, the molten phase is believed to exist, under the reaction conditions, as a coating on the solid transition metal oxide particles.

The composition of the atmosphere should also be adjusted to control the thermal decomposition of the lithium compound. For example, if lithium carbonate is used, sufficient carbon dioxide should be present in the atmosphere to retard its thermal decomposition at reaction temperature.

As a commercial process, the process of the invention has several advantages over the methods of the prior art. It has the advantage that the preparation of lithium transition metal oxides can be accomplished in a single high temperature heating step, in contrast to the prior art methods which require multiple firings under calcination conditions. Since the reaction occurs in a molten phase, instead of as a solid state reaction, it has faster kinetics, thereby producing a more uniform, homogeneous and reproducible powder product with controllable particle size and growth. Therefore, this improved process is more amenable to large scale commercial production.

Advantageously, the produced lithium transition metal oxide powders exhibit low surface area, a narrow particle size distribution, and high chemical purity. Description of the Drawings

The method of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a generalized process flowsheet for the production of lithiated transition metal dioxide powders by the process of the present invention;

Figure 2 is a photomicrograph illustrating lithium cobalt dioxide powder prepared by the process of the present invention;

Figure 3 is a photomicrograph illustrating lithium nickel dioxide powder prepared by the process of the present invention;

Figure 4 is a histogram illustrating size distribution ranges for lithium cobalt dioxide powder prepared from cobaltic oxide by the process of the present invention;

Figure 5 is a histogram illustrating size distribution ranges for lithium cobalt dioxide powder prepared from cobaltous carbonate by the process of the present invention;

Figure 6 shows the first charge and discharge of the electrochemical cell wherein the cathode was prepared of LiNiθ2 powder prepared by the process of the invention; and

Figure 7 depicts part of the life cycle of the cell of Figure 6, with voltages between 4.15 and 3.0 volts. Description of the Preferred Embodiment

A finely divided lithium compound and one or more transition metal compounds are well admixed in stoichiometric quantities, or in the case of the lithium compound in an amount slightly greater than stoichiometrically required. The mixing step is critical because a poorly mixed reactant powder could lead to a product having a particle size distribution range which is too broad because the rate of particle growth is dependent upon the dispersion of the lithium salt.

Suitable lithium compounds are those effective upon heating to exist in the molten phase with no, or only partial decomposition thereof, taking place under the reaction conditions. Such compounds would be selected from the salts, oxides or hydroxides of lithium. The preferred lithium compounds are lithium hydroxide for temperatures below and about 750°C and lithium carbonates for reaction temperatures above 750°C. If LiOH is used, thermal decomposition of the LiOH can be controlled without concomitant inhibition of the lithiation reaction, by doping the atmosphere with steam or water vapour.

The transition metal compounds would be selected from the oxides of cobalt, nickel, manganese, vanadium, iron, titanium, chromium, or mixtures thereof. Preferably, the transition metal compounds would be selected from cobalt, nickel or manganese or mixtures thereof. Alternatively, suitable transition metal compounds would be selected from the hydroxides, carbonates or salts of cobalt, nickel, manganese, vanadium or chromium or mixtures thereof. These latter transition metal compounds must be convertable to their respective oxides in-situ. It is most advantageous if the oxide added or produced in-situ is in the same oxidation state as the final product, so that the reaction can be carried out with the minimum of air or oxygen, and the stabilization of the molten lithium salt can then be effected by conducting the reaction in an enclosed atmosphere.

An additive comprising an alkali metal compound may be added to the reaction mixture. Preferably, the additive would be selected from NaOH or KOH. The amount of additive used would range from 0.1 to 50 molar % based on the transition metal content. In the case of the synthesis of lithium cobalt dioxide using the pathways described herein, it is not necessary to add an additive in order to obtain a satisfactory product. However, in the production of lithium nickel oxide or lithium manganese oxide the presence of an additive has been found to assist in optimizing the kinetics of the reaction and stabilizing the thermal decomposition of the lithium compound.

The mixture is introduced into a furnace where it is heated to temperatures ranging from 200 to 1200°C for periods of time ranging from lh to 72h. The reaction atmosphere, as stated earlier herein, must be functional to either convert the transition metal compound to its oxide and/or to maintain the transition metal oxide in the desired oxidation state, namely that of the transition metal in the final product. Thus the atmosphere may be either inert, oxidizing or reducing and is readily determined by one skilled in the art.

The product and process of the invention will now be described with reference to the following non- limitative examples.

EXAMPLE 1 •

The synthesis of lithium cobaltic dioxide to form powders suitable for use in lithium ion battery systems. Having reference to the flowsheet of Figure 1, finely divided lithium carbonate and cobal (III) oxide in stoichiometric, or slightly greater than stoichiometric amounts, are admixed in blending step 1. The cobalt (III) oxide may be synthesized by various routes as will be described hereinafter. The mixture is introduced into a furnace where it is heated in calcination step 2 to a temperature in the range of about 750 to 900°C in a static, neutral or non- oxidizing atmosphere, for a period of time of about 6 h to 72 h. Following calcination, the sintered lithium cobaltic dioxide product is pulverized to break up agglomerates using a hammermill or ball mill in milling step 3. An optional water wash follows, washing step 4, because advantageously it has been determined that water appears to remove most of the soluble impurities such as sulphur and sodium, as well as unreacted excess lithium carbonate.

It is believed that by using an essentially pure cobaltic oxide powder and lithium carbonate the process of the invention yields lithium cobaltic dioxide having a constant particle size and surface area. irrespective of the shape and size of the reaction vessel. The physical properties of the powder can be simply controlled by the furnace temperature and residence time. Additionally, if an excess of lithium carbonate is utilized (i.e. a 5 to 10% stoichiometric excess over cobalt), then a lithium to cobalt atomic ratio of 1:1 in the powder product is obtained.

The cobalt (III) oxide can be prepared by several routes, namely from cobaltic hexammine sulphate solution or cobaltic pentammine sulphate solution, by precipitation with sodium or potassium hydroxide, or from a soluble cobalt(II) salt by oxidation with a strong oxidizing agent, or from cobalt carbonate by high temperature oxidation in air, or can alternatively be obtained from commercial suppliers.

EXAMPLE 2 Preparation of Cobaltic Oxide from Cobaltic Hexammine Sulphate

72 g of sodium hydroxide (ex BDH Ltd), dissolved in one litre of water, was slowly added to a 3L solution which contained 180 g of cobaltic hexammine sulphate (ex Sherritt Inc), at 90°C. The mixture was stirred and heated to its boiling point, for 30 minutes, to drive off the coproduced ammonia. The slurry was cooled and the supernatant liquor decanted off. The black precipitate was washed twice with a similar quantity of pure water, before it was filtered and washed twice to remove soluble impurities. It was then dried in an oven at 120°C for about 24 hours. The product analyzed as hydrated cobaltic oxide with 61.1% w/w cobalt. The above procedure was repeated twice more and the product analyzed at 61.5 and 61.3% w/w cobalt. EXAMPLE 3 Preparation of Cobaltic Oxide from Cobaltous Sulphate

2.24 kg of ammonium sulphate was dissolved in 20 litres of aqueous cobaltous sulphate solution, with a cobalt concentration of 100 g/L at 50°C. 3.46 kg of ammonia (as 29% aqueous ammonia) was added slowly, until any of the intermediate precipitate had redissolved. The resultant cobaltous pentammine sulphate solution was oxidized to cobaltic pentammine sulphate by the addition of 1.28 kg of hydrogen peroxide (as a 30% solution in water).

The cobaltic pentammine sulphate solution was heated to 90°C and 4.2 L aqueous sodium hydroxide (240 g/L) added at a rate of 300 ml/min. The mixture was stirred during this addition and finally heated to its boiling point to drive off any remaining ammonia. The supernatant liquor was decanted from the settled slurry. Any soluble impurities were removed from the black precipitate by twice repulping it with pure water, followed by filtration and washing the filtrate twice more with pure water. After drying the black solid in an oven at 120°C for about 24 hours, it analyzed as hydrated cobaltic oxide with 61.1% w/w cobalt.

EXAMPLE 4 Conversion of Cobaltic Oxide into Lithium Cobaltic Dioxide over Different Time Periods

1.3 kg of dried cobaltic oxide, prepared as in Example 3 above, and 0.9 kg of lithium carbonate (ex Cyprus Foote) were mixed together in a V blender for 4 hours. 300 g aliquots of the mixture were loaded into one litre CN1000 alumina crucibles (ex Coors). Each crucible was heated in a MEY box furnace at 900°C. Individual crucibles were removed after seven different time periods (1, 3, 6, 12, 24, 36 and 48 hours). The resultant products were broken up into pieces, the size of a pea, in a mortar and pestle, and fed to a hammermill, for light deagglomeration, and the powder passed through a 400 mesh screen. The minus 400 mesh fraction was analyzed; the results are given in Table I. The particle size of the powder increases as the residence time of the reactant mixture in the furnace is increased, indicating that the particles grow in situ. The surface area of the product decreased to a constant value as the particle size increases.

TABLE I

Time (hrs) D 50% (urn) Surface Area m²/g

1 3.9 1.73

3 5.2 1.15

6 7.2 0.77

12 8.8 0.45

24 10.9 0.35

36 12.4 0.36

48 15.2 0.38 EXAMPLE 5

Conversion of Cobalt Oxide into Lithium Cobaltic Dioxide at Different Temperatures

A blend of dried cobaltic oxide and lithium carbonate was mixed as in Example 4. 300 g aliquots were loaded into one litre CN 1000 alumina crucibles and placed in the NEY furnace at different temperatures (800, 900 and 1000°C) for 36 hours. The resultant products were fed to a hammermill, for light deagglomeration, and segregated on a 400 mesh screen. The minus 400 mesh powder was analyzed and the results, given in Table II, show that the growth of the particles increases as the furnacing temperature increases. TABLιE II

Temp (°C) D 50% (urn) Surface Area ( ²/g)

800 3.6 0.98

900 12.4 0.36

1000 24.1 0.44

EXAMPLE 6

Comparison of the Synthesis of Lithium Cobaltic Dioxide from Cobaltic Oxide and Cobaltous Carbonate

Powders of either cobaltic oxide (prepared as in Example 2 above) or cobaltous carbonate (ex Aldrich Chemical) were blended with lithium carbonate, in a V blender, as in Example 4, and various amounts were charged to various sizes and shapes of alumina crucible. The mixtures were each reacted in a NEY furnace for 36 hours at 900°C, and then deagglomerated as in Example 4. The analytical results are displayed as histograms in Figures 4 and 5. From Figure 4, it can be seen that the furnaced product from cobaltic oxide has particles with a similar median and size range irrespective of the crucible size, shape or loading. Figure 5, however, shows that dioxide made from cobaltous carbonate is sensitive to crucible size, shape and loading. Two additional runs (52A and 66 in Figure 5) were carried out in which the cobaltous carbonate was first decomposed before it could react with lithium carbonate, i.e. the furnace temperature was first held at 400°C for 6 hours (to decompose the carbonate to cobalt oxide) and then the temperature was raised to 900°C to complete the reaction of the resultant oxide with lithium carbonate. The analytical results show that crucible shape and size do not now appear to affect the particle size of the lithium cobaltic dioxide. EXAMPLE 7

The effect of Excess Lithium Carbonate on the Preparation of Lithium Cobaltic Dioxide.

Mixtures of cobaltic oxide and lithium carbonate were made up as in Example 4, in which the lithium carbonate content was set at different stoichiometric excesses (-20%, 0%, 20%, 50% and 100%). Equal quantities of each mixture were treated in the furnace as before (900°C for 36 hours). The products were then analyzed, and the results are given in Table III. It can be seen that the largest particle sizes are achieved when an excess of lithium carbonate is present, indicating that particulate growth is assisted by the presence of molten lithium carbonate.

TABLE III Target (Excess %) D 50% (um) Surface Area ( ²/g)

-20 2.6 1.99

+5 12.4 0.36

+20 14.2 0.41

+50 14.2 0.46

+100 11.3 0.63

EXAMPLE 8

The Effect of Compaction on the Preparation of Lithium Cobaltic Dioxide

Cobaltic oxide and lithium carbonate were blended, as in Example 4, and the resultant powder was subjected to compaction by placing it in a 2 cm diameter mold and adding 5 tons of pressure to the piston. The 1" long compact had a density of 1.8 g/cc compared to 0.5 g/cc for the original powder blended. Several compacts were placed in a crucible and placed in a NEY furnace at 900°C for two different time periods (12 and 24 hours). The products were analyzed, and the results are given in Table IV. It can be seen that the rate of growth of the lithium cobaltic dioxide particles greatly increased when compared to the product from the original powder. In fact, the compacted product obtained after 12 hours is similar to that obtained from the uncompacted powder in 36 hours (Ref. Table 1).

TABLE IV Lithium Cobaltic Dioxide made from Compacted Powder

Time (hrs) D 50% -400 mesh

(um)

12 13.3

24 13.9

EXAMPLE 9 The synthesis of lithium nickel dioxide to form powders suitable for use in lithium ion battery systems

Having reference to the flowsheet of Figure 1, lithine, L10H.H20, nickel hydroxide, and potassium and/or sodium hydroxide are ground together and are well mixed in stoichiometric amounts in blending step 1. The mixture is introduced to a furnace where it is heated (step 2) in an oxygen containing atmosphere to a temperature in the range of 500 to 1000°C, for a period of time of about 10 to 50 hours. Following calcination, the sintered lithium nickel dioxide is optionally pulverized to break up agglomerates using a hammermill or ball mill (step 3). A water wash 4 is carried out followed by a final oven drying step 5, and classification 6 to recover the lithium nickel dioxide powder product.

EXAMPLE 10 Preparation of Lithiated Nickel Dioxide with and without Potassium Hydroxide

46g of lithine, Li0H.H₂0, 93 g of nickel hydroxide and 7.3 g of potassium hydroxide (85 % KOH) were ground and mixed together in a mortar and a pestle for about 20 minutes. The 1.1:1.0:0.1 (Li:Ni:K) mole ratio blend was heated in a furnace at 800°C for 20 hours in air, then was removed from the furnace, pulverized, washed with distilled water and dried in an oven at 150°C for 5 hours. The resultant product, which passed through a 400 mesh sieve, analyzed, by an average particle size of 11.5 microns, and BET (Brunauer-Emmett-Teller) surface area of 0.74m²/g. After reheating at 600°C for 1 hour, the surface area was reduced to 0.32 m /g. Chemical analysis indicated that the potassium content was 0.002 % by weight, that is that the potassium compounds can be washed out almost completely and that the KOH does not add impurity phases or compounds to the final iNiθ2 product.

For comparison, a second sample of L1N102 ^was prepared as described above, but without the inclusion of the potassium hydroxide. X-ray diffraction indicated that L1N102 ^{nad been} obtained, but an SEM micrograph showed that the average particle was about 3.0 microns which is significantly smaller than the particles obtained in the presence of KOH, under the same conditions.

For further comparison, a third sample of LiNiθ2 was prepared as above, but without the inclusion of the potassium hydroxide and with a larger excess of lithium hydroxide. The starting material corresponded to Li:Ni mole ratio of 1.2:1.0, that is a 20% excess lithium hydroxide, compared to 10% excess lithium hydroxide in the previous two samples. After heating the materials at 800°C for 20 hours, it was found that the particle size was also about 3.0 microns, clearly demonstrating that the presence of potassium hydroxide is necessary to increase the growth rate of LiNiθ2 particles. EXAMPLE 11 Preparation and Electrochemical Cell Performance of Lithiated Nickel Dioxide with Potassium hydroxide at a Lower Temperature

92g of lithium hydroxide, 185g of nickel hydroxide and 14.7 of potassium hydroxide (85% KOH) were ground together with a mortar and a pestle for about 20 minutes, the blend heated at 700°C for 20 hours in air, and the product pulverized then washed with water, and finally dried in an oven at 150°C. The product which passed through a 400 mesh sieve, analyzed as a single phase of LiNiθ2, with lattice constants a=2.880 A and b=14.206 A, which agree very well with the reference data (Journal of Power Sources 54 (1995) 109-114). The sample particle sizes, as viewed by SEM were between 1 and 3 microns, and an average particle size, as measured by Microtrac™ (light scattering method), of 2.5 microns. Chemical analysis gave lithium, nickel and potassium contents as 7.18% and 59.91% and 0.002% by weight respectively; the theoretical values for Ll and Ni for LiNi0 are 7.11% and 60.11%. When impurities due to the reactants are taken into account, the formula for the product was postulated to be Liι__xNiι_+x02 with- 0.02<x<0.02. The value of x in Li₁„_xNi_1+x0₂ made by other conventional methods is usually x>0.02. This indicates that a better quality product is obtained with potassium hydroxide in the reaction mixture, probably because the potassium promotes better distribution of the lithium within the melt at reaction temperature.

An electrochemical cell, with a cathode, separator, anode and an electrolyte was assembled in which the cathode was made of the LiNi0₂ powder from above, mixed to a paste, with 9% by weight of Super S carbon black and 1% by weight EPDM (ethylene propylene diene terpolymer), and spread on aluminium foil before being allowed to dry; the paste coverage was typically 20 mg/cm² and cathode area was 1.2 x 1.2 cm². The electrolyte was 1 M lithium perchlorate, L1C104 in propylene carbonate. Lithium metal was used for the anode and Isotactic Polypropylene (Celgard 2500™) as the separator. Cell hardware was stainless steel with an aluminium substrate, sealed with an O-ring and stack pressure provided by a spring. Lithium foil was attached to the stainless steel hardware and the cathode attached to the aluminum substrate. Charge current was adjusted to correspond to x-0.5 Li deintercalation in Li;_L-__χNiι_+χθ2 during a charge of 20 hours, and the discharge current adjusted to correspond to x*0.5 Li intercalation in 10 hours. The charge voltage was up to 4.15 V and the discharge voltage down to 3.0 V. Figure 6 shows the first charge and discharge curve of the cell using L1 102 as cathode materials. The first charge capacity is seen to be 200 mAh/g and the first discharge capacity 145 mAh/g. The cycle life is shown in Figure 7 with voltages between 4.15V and 3.0 V. The fade rates are very low, and significantly less than materials made by prior art at this working voltage range and at this capacity.

Example 12 Preparation of Lithiated Nickel Dioxide with Sodium Hydroxide

A sample of L1N102 was made in the same way as the first sample in Example 9, with sodium hydroxide in place of the potassium hydroxide: that is, 46g of lithine, LiOH.H₂0, 93 g of nickel hydroxide and 4.5 g sodium hydroxide (97% NaOH) were ground and mixed together in a mortar and a pestle for about 20 minutes. The 1.1:1.0:0.1 (Li:Ni:Na) mole ratio blend was heated in a furnace at 800°C for 20 hours in air, then was removed from the furnace, pulverized, washed with distilled water and dried in an oven at 150°C for 5 hours. The resultant product, which passed through a 400 mesh sieve, analyzed by X-ray diffraction as pure single phase of LiNiθ2 with a low sodium content (less than 5% of the original was left). The X-ray diffraction pattern of the LiNiθ2 product agreed with the standard data, and no impurity phase was observed. In conclusion, sodium hydroxide can be used instead of potassium hydroxide for this preparation.

Example 13 Preparation of Lithiated Cobalt Dioxide with and without Potassium Hydroxide

The effect of the potassium hydroxide on the growth rate of particles during the synthesis of lithium cobalt dioxide, LiCoθ2 was investigated. Firstly, LiCoθ2 was prepared by the same method as the first sample of L1N102 was prepared in Example 10, that is, 46g of lithine, LiOH.H₂0, 97g of cobalt oxide (containing 60% cobalt by weight) and 7.3 g potassium hydroxide (85 % KOH) were ground and mixed together in a mortar and pestle for about 20 minutes. The 1.1:1.0:0.1 (Li:Co:K) mole ratio blend was heated in a furnace at 800°C for 20 hours in air, then was removed from the furnace, pulverized, washed with distilled water and dried in an oven at 150°C for 5 hours. The resultant product, which passed through a 400 mesh sieve, analyzed by X-ray diffraction as a very pure single phase of LiCoθ2- The peak positions agree well with the standard materials, with lattice constants a-2.819+0.001 A and b»14.07+_0.01A. Microtrac™ analysis show an average particle size of 8.5 microns. Chemical analysis gave lithium and cobalt of 7.34% and 59.72% by weight, very close to 1:1 mole ratio, with a very low potassium content of 0.031%, showing that the potassium compounds can be easily washed away after the calcination reaction.

For comparison, a second sample of LiCoθ2 ^was made, as above, but without the addition of the potassium hydroxide, that is, 46g of lithine, Li0H.H₂0 and 97g of cobalt oxide (containing 60.5% cobalt by weight) were ground and mixed together in a mortar and a pestle for about 20 minutes. The 1.1:1.0 (Li:Co) mole ratio blend was heated in a furnace at 800°C for 20 hours in air, then was removed from the furnace, pulverized, washed with distilled water and dried in an oven at 150°C for 5 hours. The resultant product, which passed through a 400 mesh sieve, analyzed by X-ray diffraction as a very pure single phase of LiCoθ2 with lattice constants calculated as a=2.819+0.001 A and b«14.07+0.01A. Chemical analysis shows lithium and cobalt contents are 7.58% and 59.17%, respectively, that is the lithium ratio is slightly higher than stoichiometric requirement. However, the average particle size was only 4.9 microns, indicating that particles of LiCoθ2 prepared with the 10% potassium hydroxide in the blend grow to be almost twice as large as those obtained without potassium hydroxide, under the same conditions.

Example 14 Deagglomeration of the Product Particles by Washing or Milling

Two samples of lithium nickel dioxide were prepared by a similar method to that outlined in Example 11, except that larger crucibles were used, each containing 500 g of the reactant mixture. The calcination was carried out at two different temperatures, 750 and 800°C, with an atmosphere of oxygen present in the furnace at the lower temperature, and air instead of oxygen at the higher temperature. Two samples of the product from each calcination were treated as follows. One part was deagglomerated by lightly grinding in a ceramic ball mill, and the other part was deagglomerated by simply washing it with water. The median particle sizes of the resultant powders are given in Table V for a comparison of median particle size in um of calcined product after deagglomeration of a mill or with a simple water wash.

TABLE V Median Particle Size ( um)

750°C with 0 800°C with air Water Wash 9.7 8.0

Milling 7.4 6.3

Both treatments lead to approximately the same particle size in the final product, so there is a process choice in the post treatment of the calcined product to convert it to powder: deagglomeration in a mill, or washing with water. Figure 2 is a photograph of the particles made when lithium cobalt dioxide (as prepared in Example 4, with 36 h in the furnace) is milled to deagglomerate the product particles. Figure 3 is a photograph of the particles which result from a water wash treatment of lithium nickel dioxide, as made and treated by the procedure described in this example. Also, these results clearly demonstrate that the particles made by the process of this invention grow in a single step, and that their unique size and structure do not result from the comminution of a large calcined mass.

It will be understood, of course, that other embodiments and examples of the invention will be readily apparent to a person skilled in the art, the scope and purview of the invention being defined in the appended claims.

Claims

WE CLAIM

1. A process for the synthesis of lithium transition metal oxide powders having predetermined particle size and controlled microstructure which comprises: reacting one or more transition metal compounds with a salt, oxide or hydroxide of lithium, said lithium compound being in a molten phase, and optionally, an additive functional to increase the effective molten phase temperature range of said lithium compound, in an atmosphere functional to control the thermal decomposition of said lithium compound and to maintain, or convert and maintain, the transition metal compound in an oxidation state which corresponds to the oxidation state of the transition metal in the product, at a temperature and for a time effective to thereby form the desired lithium transition metal oxide.

2. A process as set forth in claim 1 wherein said lithium compound comprises lithium hydroxide or lithium carbonate.

3. A process as set forth in claim 2 wherein said transition metal compound is selected from a salt, oxide, or hydroxide of cobalt, nickel, manganese, vanadium, iron, titanium or chromium or mixtures thereof.

4. A process as set forth in claim 2 wherein said transition metal compound is selected from the oxides or hydroxides of cobalt, nickel, manganese or mixtures thereof.

5. A process as set forth in claim 1 wherein said additive comprises an alkali metal compound.

6. A process as set forth in claim 2 wherein said additive is selected from KOH or NaOH.

7. A process as set forth in claim 3 wherein said additive is selected from KOH or NaOH.

8. A process as set forth in claim 4 wherein said additive is selected from KOH or NaOH.

9. The process as set forth in claim 1 wherein said lithium compound comprises lithium hydroxide or carbonate, said transition metal compound comprises a salt, oxide or hydroxide of cobalt, nickel, manganese, iron, vanadium, titanium or chromium or a mixture thereof, and said additive is potassium hydroxide or sodium hydroxide.

10. The process as set forth in claim 1 wherein said lithium compound comprises lithium hydroxide or lithium carbonate, said transition metal compound comprises an oxide or hydroxide of cobalt, and said additive is potassium hydroxide.

11. The process as set forth in claim 1 wherein said lithium compound comprises lithium hydroxide or lithium carbonate, said transition metal compound comprises an oxide or hydroxide of nickel, and said additive is potassium hydroxide.

12. The process as set forth in claim 1 wherein said lithium compound comprises lithium hydroxide or lithium carbonate, said transition metal compound is an oxide or hydroxide of manganese, and said additive is selected from potassium or sodium hydroxide.

13. The process as set forth in claim 1 wherein the thermal decomposition of said molten lithium compound is controlled by the addition of gases to the atmosphere thereabove.

14. The process as set forth in claim 2 wherein the thermal decomposition of said molten lithium compound is controlled by the addition of gases to the atmosphere thereabove.

15. The process as set forth in claim 1 wherein said lithium compound comprises lithium hydroxide and water is added to the atmosphere thereabove, to thereby control the thermal decomposition of said molten lithium compound.

16. The process as set forth in claim 3 wherein said lithium compound comprises lithium hydroxide and water is added to the atmosphere thereabove, to thereby control the thermal decomposition of said molten lithium compound.

17. The process as set forth in claim 9 wherein said lithium compound comprises lithium hydroxide and water is added to the atmosphere thereabove, to thereby control the thermal decomposition of said molten lithium compound.

18. The process as set forth in claim 1 wherein said lithium compound comprises lithium carbonate and carbon dioxide is added to the atmosphere thereabove to thereby control thermal decomposition of the lithium compound.

19. The process as set forth in claim 3 wherein said lithium compound comprises lithium carbonate and carbon dioxide is added to the atmosphere thereabove to thereby control thermal decomposition of the lithium compound.

20. The process as set forth in claim 9 wherein said lithium compound comprises lithium carbonate and carbon dioxide is added to the atmosphere thereabove to thereby control thermal decomposition of the lithium compound.

21. A lithiated transition metal oxide powder prepared by the process of claim 1.

22. A lithiated transition metal oxide powder prepared by the process of claim 3.

23. A lithiated transition metal oxide powder prepared by the process of claim 9.

24. A lithium cobalt oxide powder prepared by the process of claim 4.

25. A lithium cobalt oxide powder prepared by the process of claim 12.

26. A lithium nickel oxide powder prepared by the process of claim 4.

27. A lithium nickel oxide powder prepared by the process of claim 13.

28. A lithium manganese oxide powder prepared by the process of claim 4.

29. A lithium manganese oxide powder prepared by the process of claim 15.

30. Lithium transition metal oxide powder forming discrete particles and having a particle size distribution ranging from about 0.5 to 25 microns and a surface area ranging from about 5 to 0.1m /g.

31. Lithium cobalt oxide powder forming discrete particles and having a particle size distribution ranging from about 0.5 to 25 microns and a surface area ranging from about 5 to 0.1m /g.

32. Lithium nickel oxide powder forming discrete particles and having a particle size distribution ranging from about 0.5 to 25 microns and a surface area ranging from about 5 to 0.1m /g.

33. Lithium manganese oxide powder forming discrete particles and having a particle size distribution ranging from about 0.5 to 25 microns and a surface area ranging from about 5 to 0.1m /g.