WO2014117394A1

WO2014117394A1 - Method of making active materials for use in secondary electrochemical cells

Info

Publication number: WO2014117394A1
Application number: PCT/CN2013/071281
Authority: WO
Inventors: Xueping GONG; Qifan ZOU; Li Wang
Original assignee: Valence Technology Inc
Current assignee: Valence Technology Inc
Priority date: 2013-02-01
Filing date: 2013-02-01
Publication date: 2014-08-07
Anticipated expiration: 2015-08-01

Abstract

A method for producing metal phosphates or mixed metal phosphates and in particular lithiated metal phosphates and mixed metal phosphates. It comprises a series of steps. In the first step, the weighted starting materials are dispersed and mixed in a solvent to form a slurry. Slurry is spray dried to produce a powder mixture. The powder mixture is milled to obtain a milled powder. The milled powder is pelletized and sintered for a time and at a temperature sufficient to form the electroactive material in its first form. The electroactive material in its first form is then milled to form the electroactive material in its second form. The milled electroactive material is then subjected to a mechanofusion process to produce the final electroactive material.

Description

METHOD OF MAKING ACTIVE MATERIALS FOR USE IN SECONDARY

ELECTROCHEMICAL CELLS

FIELD OF THE INVENTION

The present invention relates to the commercial synthesis of electroactive lithium metal phosphate materials for use in electrodes, more specifically for use as cathode active materials in lithium ion batteries.

BACKGROUND OF THE FNVENTION

A wide variety of electrochemical cells or batteries are known in the art. In general, batteries are devices that convert chemical energy into electrical energy, by means of an electrochemical oxidation-reduction reaction. Batteries are used in a wide variety of applications, particularly as a power source for devices that cannot practicably be powered by centralized power generation sources (e.g., by commercial power plants using utility transition lines).

Batteries can generally be described as comprising three components: an anode that contains a material that is oxidized (yields electrons) during discharge of the battery; a cathode that contains a material that is reduced (accepts electrons) during discharge of the battery; and an electrolyte that provides for transfer of ions between the cathode and anode. Batteries can be more specifically characterized by the specific materials that make up each of these three components. Selection of these components can yield batteries having specific voltage and discharge characteristics that can be optimized for particular applications.

The electrodes of such batteries generally include an electroactive material. Recently a class of transition metal phosphates and mixed metal phosphates have been developed for use as electroactive material. These transition metal phosphates and mixed metal phosphates are insertion based compounds and allow great flexibility in the design of lithium ion batteries. These phosphate compounds have a crystal lattice structure or framework from which ions, such as lithium ions, can be extracted and subsequently reinserted and/or from which ions such as lithium ions can be inserted or intercalated and subsequently extracted.

A class of such materials is disclosed in U.S. 6,528,033 Bl (Barker et al). The compounds therein are of the general formula LiaMIbMIIc(P04)d wherein MI and Mil are the same or different. MI is a metal selected from the group consisting of Fe, Co, Ni, Mn, Cu, V, Sn, Cr and mixtures thereof. Mil is optionally present, but when present is a metal selected from the group consisting of Mg, Ca, Zn, Sr, Pb, Cd, Sn, Ba, Be and mixtures thereof. U.S. 6,528,033 Bl (Barker et al.) further discloses useful electroactive materials of the formula LiFei__xMg_xP0₄.

In general, such an electroactive material must exhibit a low free energy of reaction with lithium, be able to intercalate a large quantity of lithium, maintain its lattice structure upon insertion and extraction of lithium, allow rapid diffusion of lithium, afford good electrical conductivity, not be significantly soluble in the electrolyte system of the battery, and be readily and economically produced. However, many of the electroactive materials known in the art lack one or more of these characteristics.

Transition metal phosphates are typically synthesized in a solid state reaction.

Starting materials in particle form are mixed to produce an intimate mixture of particles. When heat is applied to effect reaction, the solid particles react with one another through a variety of surface reactions accompanied by diffusion of reactive materials into and out of various particles in the mixture. For this reason, it is preferred to mix particle mixtures with as close a degree of contact as possible between the particles together with a desirable particle size. To accomplish this, the particle mixtures are typically prepared by using methods such as ball milling or physical mixing.

For instance a lithium metal phosphate made, for example, from L1H₂PO₄ and a metal oxide via high calcination requires that starting materials be fine size particles. Intensive mixing is needed to insure complete conversion of the starting materials to the desired end product. Thus, it would be desirable and beneficial to have a process for preparing such intercalation materials more efficiently, at reduced cost and with less consumption of production space and reduction of production time. The inventors of the present invention have now found a reproducible, efficient and economical method for producing high density, high purity electroactive materials for use in the production of electrodes and in particular in the production of cathodes.

SUMMARY OF THE INVENTION

The present invention provides a method for producing particles of metal phosphates or particles of mixed metal phosphates and in particular lithiated metal phosphates and mixed metal phosphates. It comprises a series of steps. In the first step the weighted starting materials are dispersed and mixed in a solvent to form a slurry. The mixed slurry is spray dried to produce a powder mixture. The spray dried powder mixture is milled to obtain a fine milled powder. The fine milled powder is compacted to form a compact pellet and then the pellet is sintered for a time and at a temperature sufficient to form the electroactive material in its first form. The electroactive material in its first form is then milled to form the electroactive material in its second form. The electroactive material in its second form is then subjected to a mechano fusion process to produce the final electroactive material.

This process improves the physical characteristics of as-synthesized electroactive materials. The powder resulting from this process has high tap density, uniform particle size and spherical particles with carbon enriched surfaces. Using a solvent for mixing the starting materials allows for a more homogenous mixing of the starting materials when compared to a solid state reaction. Milling the spray dried powder produces a fine powder which particles have a high surface area and makes it highly reactive in the subsequent sintering step. Compacting the milled powder makes the particles contact more tightly which improves the reaction in the sintering step thereby giving a more complete reaction. The mechanofusion step sphericalizes the particles and produces a product with high tap density. After the mechanofusion step, the tap density of product increases by 40-50% to 1.5g/mL.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a typical process flow chart of producing the electroactive material.

Figure 2 shows the SEM photo of the spray dried composition.

Figure 3 shows the SEM photo of the jet milled product.

Figure 4 shows the SEM photo of the pulverized product.

Figure 5 shows the SEM of the mechanofused powder.

DETAILED DESCRIPTION OF THE INVENTION

Specific benefits and embodiments of the present invention are apparent from the detailed description set forth herein below. It should be understood, however, that the detailed description and specific examples, while indicating embodiments among those preferred, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

A wide variety of commercially useful electroactive active materials are disclosed and can be made by the carbothermal processes described in U.S. 6,528,033; U.S. 6,716,372; U.S. 6,702,961; U.S. 6,913,855; U.S.6,730,281 and U.S. 7,060,206. Electroactive materials are materials which find use in the manufacture of electrodes, namely, cathodes and anodes. Such cathodes and anodes are then used in the production of electrochemical cells. In general, the useful electroactive materials are prepared by mixing a source of metal ion, a source of alkali metal ion, a source of phosphate, a source of carbon and optionally a source of a second metal ion. Such mixture is then heated in an inert atmosphere. For example, it has been disclosed that LiFei__xMg_xP0₄ (lithium iron magnesium phosphate) can be prepared by mixing the reactants L1H₂PO₄, Fe₂03, Mg(OH)₂ and carbon and heating said reaction mixture in an inert atmosphere.

Known methods for preparing lithium metal phosphates, on a commercial scale, involve measuring and mixing the precursor compounds, such as a lithium compound, a phosphate compound, at least a metal compound and carbon. The resulting mixture is then mulled and pelletized. The pellet is then fired to form the electroactive material in its first form. This product is then milled and sieved to give the electroactive materials in a more desirable form for producing electrodes. Such products produced on a small scale have not always provided an optimal electroactive material for producing electrodes at a commercial scale.

In the present invention, on a commercial scale, the precursor compounds, such as a lithium compound, a phosphate compound, a transition metal compound and carbon are measured, dispersed and mixed in a solvent such as water or an organic material to form a slurry. Organic materials include without limitation ethanol, propanol, isopropanol, acetone, butanol, isobutanol, low molecular weight alkanes, low molecular weight ketones, and the like. A preferred solvent is water. The slurry is then spray dried by commercially known spray drying methods to form a powder mixture. The spray dried powder mixture is then milled to form a milled powder. The milled powder is then compacted to form a compact pellet. The pellet is then sintered to form the electroactive material in its first form. This electroactive material in its first form is then milled to give the electroactive material in its second form. Finally, the electroactive material in its second form is subjected to a mechanofusion process to produce the electroactive material in its final form. The electroactive material in final form is used for making electrodes, and more specifically cathodes.

It has now been found that using a solvent for mixing the starting materials allows for a more homogenous mixing of the starting materials when compared to a solid state reaction. It has also been found that milling the spray dried powder produces a fine powder which particles have a high surface area and makes the fine powder highly reactive in the subsequent sintering step. Compaction makes the particles contact more tightly which benefits the sintering step with a complete reaction. Further, the mechanofusion step sphericalizes the particles and produces a product with high tap density. After the mechanofusion step, the tap density of product increases by 40-50% to 1.5g/mL.

It has now been found that processing the electroactive material in its second form in a mechanofusion system can produce the electroactive material in a more desirable form. By more desirable is meant better purity, higher tap density, uniform particle size and the like.

Hence, for example, on a commercial scale, the precursor compounds, such as a lithium compound, a phosphate compound, a transition metal compound, carbon and optionally a second metal compound are measured and wet ball mixed to form a slurry. The slurry is then spray dried by commercially known spray drying methods to produce a spray dried mixture. The spray dried mixture is then milled to form a milled powder. The milled powder is then compacted to form a compact pellet. The pellet is then fired (heated, sintered) to form the electroactive product in its first form. The electrode active material in its first form is then milled to give the electroactive material in its second form. The electroactive material in its second form is then milled at least one or more times and then subjected to the mechanofusion process to give a preferred and desirable electroactive material in its final form. Such electroactive materials in its final form are then useful for preparing electrode films for use in electrochemical cells.

The powdered precursor composition of the invention is conveniently prepared by spray drying a slurry. As used here, slurry refers to a composition having a liquid phase and a solid phase. The solid phase is dispersed or suspended in the liquid phase in such a way that the composition maintains a uniform structure or stable suspension for a time period sufficient for it to be subsequently used. In the present invention, the slurry is to remain stable for a time sufficient for it to be used in the spray drying process.

The slurry is a physical mixture, distinguishing it from a true solution. As a physical mixture, the slurry can be separated into its liquid and solid components by a variety of physical processes such as centrifugation and filtration. In some embodiments, it may be susceptible to separating upon standing by the working of gravity on the solid particles in the solid phase. The slurries are preferably characterized in that when separation occurs such as by any of the mechanisms above, they can be readily re-suspended or re-dispersed by agitation.

In practice, the slurry is preferably a stable, essentially uniform composition suitable for uses that take advantage of its uniform composition. An example of such a use, as described above, is spray drying. The stability of the slurry may be maintained by physical processes such as constant agitation, or alternatively it may be enhanced by the addition of other compounds or compositions which act as a dispersing agent or suspending agent. Such optional dispersing agents are discussed below.

Slurries of the invention are prepared by combining a number of starting materials with a solvent. The solvent is preferably any liquid such as an organic liquid or water that will disperse or suspend the starting materials so that they may be used in a subsequent spray draying process. Examples of useful organic materials include without limitation ethanol, propanol, isopropanol, acetone, butanol, isobutanol, low molecular weight alkanes, low molecular weight ketones, and the like. A preferred solvent is water.

An advantage of the slurry method, of the present invention, is that starting materials may be used that are not limited to those available as particles. In particular, for the phosphate active materials, phosphoric acid H₃PO₄ may be used as a starting material. This has an added advantage in that it is considerably cheaper than the phosphate salts generally used in such solid state reactions. Although the slurries are not limited to those containing water, the slurry of the invention will be described below with respect to using water as a solvent.

The slurry of the invention is spray dried by conventional means to yield a powder precursor composition (powder mixture). The slurry is spray dried by atomizing the slurry to form droplets and contacting the droplets with a stream of gas at a temperature sufficient to evaporate at least a major portion by weight of the solvent used in the slurry. Air can be used to dry the slurry of the invention. It may be preferable to use a less oxidizing or perhaps an inert gas or gas mixture. For example, an inert gas is preferred when the slurry being dried contains organic solvents. On the other hand, hot air is suitable for drying aqueous slurries.

The spray dried mixture can be ground in any jet mill, which are commonly known in the art such as those discussed in Robert H. Perry and Don W. Green, Perry's Chemical Engineer's Handbook, 7th Ed. McGraw Hill, NY, pp. 20-47 to 20-48, 1997. Without being bound by theory, the particles become entrained in a fluid and collide with each other and are intimately dispersed and ground through colliding interactions with each constituent in the mixture. The mill produces a particularly fine particulate product where the particles that are being entrained in the fluid-flow flow smoothly, and do not have a strong interaction with each other so as to "stick" together. The particles in the jet mill are preferably able to freely interact with one another without becoming intermeshed with one another in the final milled product. Most of the milling process in a jet mill comes about by the interaction of the material being milled. If the material being milled is not free to interact with the other particles in the mill then the milling process is not as effective. The spray dried mixture is placed into the hopper, and then fed into the milling area, of the jet-mill. One such feed mechanism includes a screw type feeder that continually places a relatively constant amount of material into the jet mill. Once the material is fed into the milling area it becomes entrained in a fluid stream. One example is a pressurized stream of clean dry air. Such a stream of hot dry air at about 80 psi is preferred in the present invention. The product is collected on a filter which is later cleared by pulsing air on the side opposite of the filter from the collection side.

A mechanofusion process involves subjecting one or more powders (for example lithium iron magnesium phosphate and carbon) to intense shearing and compression forces which generate sufficient heat energy to fuse the powder particles together. This process may be used to fuse particles of one material onto other particles of the same material, or to fuse particles of one material onto a different material for example, to combine a carbonaceous material with a base material such as lithium iron magnesium phosphate. The final electroactive powder has high tap density and uniform particle size and may be used to form high quality electrodes.

Without being limited thereby, it is believed that when a compressive force and a shearing force are applied to combine the carbonaceous material and a metal phosphate or mixed metal phosphate (base materials) that the base material and the carbonaceous material are brought into intimate contact with each other. It is believed that they are physically bonded to each other and to themselves by van der Waals forces, thereby forming the final electroactive materials in a desirable powder form.

Thus, in a preferred method the metal phosphates or mixed metal phosphates are first prepared by weighing, dispersing and mixing the precursor materials in water to form a slurry. The slurry is then spray dried to form a powdered mixture and then the powdered mixture is then milled to form a milled powder. The milled powder is then compacted to form a compact pellet. The pellet is then sintered to produce the electroacive material in its first form. The resulting electroactive material in its first form is then milled, at least once to form the electroactive material in its second form. The electroactive material in its second form is then processed in a mechanofusion type mixer capable of applying shear and compression forces to the particles (such as commercially available products of Hosokawa Micron Corporation).

The operational conditions of such mechanofusion mixers are not specifically limited but usually the rotation speed is from about 800 rpm to about 3000 rpm and more preferably from about 900 rpm to about 2650 rpm. The mixing time likewise is not specifically limited but typically is about 5 minutes to about 90 minutes and more preferably is from about 20 minutes to about 30 minutes. A more detailed description of a mechanofusion process and process parameters can be found in U.S. 5,081,072 (Hosokawa et al.), hereby incorporated by reference.

It is believed that such process would be beneficial for producing, on a commercial scale, electroactive materials ("electrode active materials") comprising at least lithium or other alkali metals, at least one transition metal and a phosphate or similar moiety. Such electrode active materials include those of the nominal general formula A_aM_b(XY₄)_cZ_d, wherein a, b and c are greater than zero and d is greater than or equal to zero. (As used herein, the term "include," and its variants, is intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that may also be useful in the materials, compositions, devices and methods of this invention).

A is selected from the group consisting of Li (lithium), Na (sodium), K (potassium), and mixtures thereof. In a preferred embodiment, A is Li, or a mixture of Li with Na, a mixture of Li with K, or a mixture of Li, Na and K. In another preferred embodiment, A is Na, or a mixture of Na with K. Preferably "a" is from about 0.1 to about 6, more preferably from about 0.2 to about 6. Where c = 1, a is preferably from about 0.1 to about 3, preferably from about 0.2 to about 2. In a preferred embodiment, where c = 1, a is less than about 1. In another preferred embodiment, where c = 1, a is about 2. Where c = 2, a is preferably from about 0.1 to about 6, preferably from about 1 to about 6. Where c = 3, a is preferably from about 0.1 to about 6, preferably from about 2 to about 6, preferably from about 3 to about 6.

M comprises one or more metals, comprising at least one transition metal capable of undergoing oxidation to a higher valence state. In a preferred embodiment, removal of alkali metal from the electrode active material is accompanied by a change in oxidation state of at least one of the metals comprising M. The amount of said metal that is available for oxidation in the electrode active material determines the amount of alkali metal that may be removed. Such concepts are, in general application, well known in the art, e.g., as disclosed in U.S. Patent 4,477,541, Fraioli, issued October 16, 1984; and U.S. Patent 6,136,472, Barker, et al, issued October 24, 2000, both of which are hereby incorporated by reference.

M may be, in general, a metal or other element, selected from the group consisting of elements from Groups 2 - 14 of the Periodic Table. As referred to herein, "Group" refers to the Group numbers (i.e., columns) of the Periodic Table as defined in the current IUPAC Periodic Table. See, e.g., U.S. Patent 6,136,472, Barker et al, issued October 24, 2000, hereby incorporated by reference. Also as referred to herein, "transition metal" will refer to elements of Groups 4-11 of the Periodic Table, while "non-transition metal" will refer to elements from Groups 2, 3, 12, 13, or 14 of the Periodic Table, excluding C and Si, and to Sb, Bi, Te, and Po from Groups 15 and 16.

In a preferred embodiment, M comprises one or more transition metals from

Groups 4 to 11. In another embodiment, M further comprises one or more non-transition metals. In preferred embodiments, the non-transition metals include those that have a +2 or a +3 oxidation state. Thus, M may be represented by MI_X MIIi__x, where MI comprises at least a transition metal and Mil a non-transition metal, and x is greater than zero. Preferably, x is greater than or equal to about 0.5, more preferably greater than or equal to about 0.8, and more preferably greater than or equal to about 0.9. Preferred transition metals include the first row transition series (the 4th Period of the Periodic Table), selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and mixtures thereof. Particularly preferred transition metals include Fe, Co, Mn, Cu, V, Cr, and mixtures thereof. Mixtures of transition metals may also be used. Although, a variety of oxidation states for such transition metals are available, in some embodiments it is preferred that the transition metals have a +2 oxidation state. In other embodiments, the transition metals have a +3 oxidation state. In a preferred embodiment, the transition metal includes at least Fe.

M may also comprise non-transition metals and metalloids. Among such elements are those selected from the group consisting of Group 2 elements, particularly Be (Beryllium), Mg (Magnesium), Ca (Calcium), Sr (Strontium), Ba (Barium); Group 3 elements, particularly Sc (Scandium), Y (Yttrium), and the lanthanides, particularly La (Lanthanum), Ce (Cerium), Pr (Praseodymium), Nd (Neodymium), Sm (Samarium); Group 12 elements, particularly Zn (zinc) and Cd (cadmium); Group 13 elements, particularly B (Boron), Al (Aluminum), Ga (Gallium), In (Indium), Tl (Thallium); Group 14 elements, particularly Si (Silicon), Ge (Germanium), Sn (Tin), and Pb (Lead); Group 15 elements, particularly As (Arsenic), Sb (Antimony), and Bi (Bismuth); Group 16 elements, particularly Te (Tellurium); and mixtures thereof. Preferred non-transition metals include the Group 2 elements, Group 12 elements, Group 13 elements, and Group 14 elements. Particularly preferred non-transition metals include those selected from the group consisting of Mg, Ca, Zn, Sr, Pb, Cd, Sn, Ba, Be, Al, and mixtures thereof. Particularly preferred non-transition metals are selected from the group consisting of Mg, Ca, Zn, Ba, Al, and mixtures thereof. More preferably, the non-transition metal is Mg. As further discussed herein, "b" is selected so as to maintain electroneutrality of the electrode active material. Preferably, b may range from about 0.8 to about 3, more preferably from about 0.8 to 2. In a preferred embodiment, where c = 1, b is from about 1 to about 2, preferably about 1. In another preferred embodiment, where c = 2, b is from about 2 to about 3, preferably about 2.

XY₄ is selected from the group consisting of X'0₄__xY'_x, XO₄__yY'2_y, X"S₄, and mixtures thereof, where X' is P (phosphorus), As (arsenic), Sb (antimony), Si (silicon), Ge (germanium), V (vanadium), S (sulfur), or mixtures thereof; X" is P, As, Sb, Si, V, Ge or mixtures thereof. In a preferred embodiment, X' and X" are, respectively, selected from the group consisting of P, Si, and mixtures thereof. In a particularly preferred embodiment, X' and X" are P. Y' is halogen (preferably fluorine), N, or S. Representative examples of moieties XY₄ include, without limitation, phosphate, silicate, sulfate, and arsenate. Other non-limiting examples include germanate, antimonate, and vanadate, as well as sulfur containing analogs of any of the foregoing.

In a preferred embodiment 0 < x < 3; and 0 < y < 4, such that a portion of the oxygen (O) in the XY₄ moiety is substituted with halogen, S, or N. In another preferred embodiment, x and y are 0. In a particularly preferred embodiment XY₄ is X'0₄, where X' is preferably P or Si, more preferably P.

Z is OH, halogen, or mixtures thereof. In a preferred embodiment, Z is selected from the group consisting of OH (hydroxyl), F (fluorine), CI (chlorine), Br (bromine) and mixtures thereof. In a preferred embodiment, Z is OH. In another preferred embodiment, Z is F, or mixtures of F with OH, CI, or Br. In a preferred embodiment, d = 0. In another preferred embodiment, d is > 0, preferably from about 0.1 to about 6, more preferably from about 0.2 to about 6. In such embodiments where d is > 0, where c = 1, d is preferably from about 0.1 to about 3, preferably from about 0.2 to about 2. In a preferred embodiment, where c=l, d is about 1. Where c = 2, d is preferably from about 0.1 to about 6, preferably from about 1 to about 6. Where c = 3, d is preferably from about 0.1 to about 6, preferably from about 2 to about 6, preferably from about 3 to about 6.

The composition of M, X, Y, and Z, and the values of a, b, c, d, x and y, are selected so as to maintain electroneutrality of the electrode active material. As referred to herein "electroneutrality" is the state of the electrode active material wherein the sum of the positively charged species (e.g., M and X) in the material is equal to the sum of the negatively charged species (e.g., Y and Z) in the material. Preferably, the XY₄ moieties are comprised to be, as a unit moiety, an anion having a charge of -2, -3, or -4, depending on the selection of X. When XY₄ represents a combination of groups, the negative charge contributed by the XY₄ groups may take on non-integer values.

In one aspect, the electroactive materials are lithium metal phosphates of general formula

Li_a M_b P0₄

with M as defined above. In a preferred embodiment, a is from about 0.3 to about 1.2, preferably from about 0.8 to 1.2, and b is about 0.8 to about 1.2. In one embodiment, a and b are both about 1. When b is about 1, the active materials may be written as Lia MI_X MIIi__x P0₄, where x is greater than zero. MI comprises at least a transition metal, preferably V, Cr, Mn, Fe, Co, Ni, Mo or combinations thereof, and more preferably Fe or mixture of Fe and V. Mil comprises a non-transition metal, preferably Be, Mg, Ca, Sr, Ba, Zn, or combinations thereof, and more preferably Mg. In one preferred embodiment, MI is Fe, Mil is Mg, and x is greater than 0.5. In another embodiment, x is greater than or equal about 0.8; in yet another embodiment, x is greater than or equal about 0.9. Preferably, x is less than or equal to about 0.95.

Other preferred embodiments of phosphate materials that can be processed by the present mechanofusion method can be represented by the formula

A_aM_b(P0₄)_cZ_d

wherein A is an alkali metal or mixture of alkali metals, M comprises at least one transition metal capable of undergoing oxidation to a higher oxidation state than in the general formula, Z is selected from the group consisting of halogen, hydroxide, and combinations thereof, a, b, and c are greater than zero and d is zero or greater.

In one embodiment, the electroactive material comprises a compound of the formula

Li_aM_b(P0₄)Z_d,

wherein

(a) 0.1 < a < 4;

(b) M is M'i__mM"_m, where M' is at least one transition metal from Groups 4 to 11 of the Periodic Table; M" is at least one element which is from Group 2, 12, 13, or 14 of the Periodic Table, 0 < m < 1, and 1 < b < 3; and

(c) Z comprises halogen, and 0 < d < 4, preferably 0.1 < d < 4;

wherein M, Z, a, b, and d are selected so as to maintain electroneutrality of said compound. Preferably, M' is selected from the group consisting of Fe, Co, Ni, Mn, Cu, V, Zr, Ti, Cr, and mixtures thereof; more preferably M' is selected from the group consisting of Fe, Co, Mn, Cu, V, Cr, and mixtures thereof. Preferably, M" is selected from the group consisting of Mg, Ca, Zn, Sr, Pb, Cd, Sn, Ba, Be, Al, and mixtures thereof; more preferably M" is selected from the group consisting of Mg, Ca, Zn, Ba, Al, and mixtures thereof. Preferably Z comprises F.

Another preferred phosphate compound comprises a compound of the formula

A₂M(P0₄)Z_d,

wherein

(a) A is selected from the group consisting of Li, Na, K, and mixtures thereof;

(b) M is M'i__bM"_b, where M' is at least one transition metal from Groups 4 to 11 of the Periodic Table; and M" is at least one element which is from Group 2, 3, 12, 13, or 14 of the Periodic Table, and 0 < b < 1; and

(c) Z comprises halogen, and 0 < d < 2, preferably 0.1 < d < 2; and

wherein M, Z, b, and d are selected so as to maintain electroneutrality of said compound.

Preferably A is Li, or mixtures of Li with Na, K, or mixtures of Na and K. Preferably, M' is selected from the group consisting of Fe, Co, Mn, Cu, V, Zr, Ti, Cr, and mixtures thereof; more preferably M' is selected from the group consisting of Fe, Co, Mn, Cu, V, Cr, and mixtures thereof. Preferably, M" is selected from the group consisting of Mg, Ca, Zn, Sr, Pb, Cd, Sn, Ba, Be, Al, and mixtures thereof; more preferably, M" is selected from the group consisting of Mg, Ca, Zn, Ba, Al, and mixtures thereof. Preferably, Z comprises F. In a preferred embodiment M' comprises Fe and M" is Mg. In another preferred embodiment M' comprises Fe and V, M" is Mg. A particularly preferred embodiment is LiFei__xMg_xP0₄, LiFei__xV_xP0₄, LiFei__x__yV_xMg_yP0₄ and Li₂Fei__xMg_xP0₄F. Preferred electrode active materials include for example LiFeo.95Mgo.osP0₄, LiFeo.95Vo.osP0₄, LiFeo. sVo.o₂Mgo.o3P0₄.

Materials such as those above and others can be made by a process comprising the step of wet ball milling a particulate precursor composition in a solvent. The particulate precursor composition is provided in the form of particles, wherein the particles have an average size of less than 100 micrometers, and wherein at least a major fraction of the particles contain at least one compound that is a source of alkali metal and at least one compound that is a source of transition metal. The precursor composition particles further comprise a carbonaceous material. In a preferred embodiment, the average particle diameter is less than 50 micrometers. Preferred transition metal compounds include those of vanadium, chromium, manganese, iron, cobalt, nickel, molybdenum, titanium, and combinations thereof, while preferred alkali metal compounds include those of lithium. In a preferred embodiment, the particles further comprise at least one compound that is a source of an anion selected from the group consisting of phosphate, hydrogen phosphate, dihydrogen phosphate, and mixtures thereof. Alternatively, the anion can be in liquid form such as phosphoric acid.

As discussed above, electroactive materials are prepared by milling and mixing precursor materials in water, spray drying the slurry so formed to form a powder, milling the spray dried powder composition and then sintering for a time and at a temperature sufficient to form an electroactive reaction product in a first form. The electroactive material is then milled and subjected to mechano fusion to produce the electroactive material in its final form.

As used herein, slurry refers to a composition having a liquid phase and a solid phase. The liquid phase may contain one or more dissolved solids. The solid phase is dispersed or suspended in the liquid phase in such a way that the composition maintains a uniform structure or stable suspension for a time period sufficient for it to be subsequently used. Formation of the slurry is beneficial over solid state mixing in that it provides a more homogenous mixture. In the present process, the slurry is to remain stable for a time sufficient for it to be used in the spray drying process.

The slurry is a physical mixture of dissolved and non-dissolved solids, distinguishing it from a true solution. As a physical mixture, the slurry can be separated into its liquid and solid components by a variety of physical processes such as centrifugation and filtration. In some embodiments, it may be susceptible to separating upon standing by the working of gravity on the solid particles in the solid phase. The slurries are preferably characterized in that when separation occurs such as by any of the mechanisms above, they can be readily re-suspended or re-dispersed by agitation.

In practice, the slurry is preferably a stable, essentially uniform composition suitable for uses that take advantage of its uniform composition. An example of such a use, as described above, is spray drying. The stability of the slurry may be maintained by physical processes such as constant agitation, or alternatively it may be enhanced by the addition of other compounds or compositions which act as a dispersing agent or suspending agent as known in the art.

Slurries are prepared by combining a number of starting materials with a solvent. The solvent is preferably any liquid such as an organic liquid or water that will disperse or suspend the starting materials so that they may be used in a subsequent spray draying process. Examples of useful organic materials include without limitation ethanol, propanol, isopropanol, butanol, isobutanol, low molecular weight alkanes, low molecular weight ketones, and the like. A preferred solvent is water. Slurries for preparing electroactive materials of general formulae given above are readily prepared according previously disclosed methods. According to the desired values of a, b, c, and d in the product, starting materials are chosen that contain "a" moles of alkali metal A from all sources, "b" moles of metals M from all sources, "c" moles of phosphate (or other XY₄ species) from all sources, and "d" moles of halide or hydroxide Z, again taking into account all sources. As discussed below, a particular starting material may be the source of more than one of the components A, M, XY₄, or Z. Alternatively, it is possible to run the reaction with an excess of one or more of the starting materials. In such a case, the stoichiometry of the product will be determined by the limiting reagent among the components A, M, XY₄, and Z. Because in such a case at least some of the starting materials will be present in the reaction product mixture, it is usually desirable to provide the starting materials in molar equivalent amounts.

Sources of alkali metal include any of a number of salts or ionic compounds of lithium, sodium or potassium. Lithium compounds are preferred. Preferably, the alkali metal source is provided in powder or particulate form. A wide range of such materials are well known in the field of inorganic chemistry. Non-limiting examples include the lithium, sodium, and/or potassium fluorides, chlorides, bromides, iodides, nitrates, nitrites, sulfates, hydrogen sulfates, sulfites, bisulfites, carbonates, bicarbonates, borates, phosphates, hydrogen ammonium phosphates, dihydrogen ammonium phosphates, silicates, antimonates, arsenates, germinates, oxides, acetates, oxalates, and the like. Hydrates of the above compounds may also be used, as well as mixtures. In particular, the mixtures may contain more than one alkali metal so that a mixed alkali metal active material will be produced in the reaction.

Sources of metals M include salts or compounds of any of the transition metals, alkaline earth metals, or lanthanide metals, as well as of non-transition metals such as aluminum, gallium, indium, thallium, tin, lead, and bismuth. The metal compounds include, without limitation, fluorides, chlorides, bromides, iodides, nitrates, nitrites, sulfates, hydrogen sulfates, sulfites, bisulfites, carbonates, bicarbonates, borates, phosphates, hydrogen ammonium phosphates, dihydrogen ammonium phosphates, silicates, antimonates, arsenates, germanates, oxides, hydroxides, acetates, oxalates, and the like. Hydrates may also be used, as well as mixtures of metals, as with the alkali metals, so that alkali metal mixed metal active materials are produced. The metal M in the starting material may have any oxidation state, depending on the oxidation state required in the desired product and the oxidizing or reducing conditions contemplated in the process. The metal sources are chosen so that at least one metal in the final reaction product is capable of being in an oxidation state higher than it is in the reaction product.

Sources of the desired starting material anions such as the phosphates (and similar moieties), halides, and hydroxides include a number of salts or compounds containing positively charged cations in addition to the source of phosphate (or other XY₄ species), halide, or hydroxide. Such cations include, without limitation, metal ions such as the alkali metals, alkaline metals, transition metals, or other non-transition metals, as well as complex cations such as ammonium or quaternary ammonium. The phosphate anion in such compounds may be phosphate, hydrogen ammonium phosphate, or dihydrogen ammonium phosphate. Hydrates of any of the above may be used, as can mixtures of the above.

Other sources of phosphate, silicate, sulfate, and other similar moieties include the acids, which are usually available in a liquid form as either the pure compound or a concentrated aqueous solution. A preferred phosphate source, for example, is concentrated orthophosphoric acid, available as approximately an 85% by weight solution in water.

A starting material may provide more than one of the components A, M, XY₄, and

Z, as is evident in the list above. In various embodiments of the invention, starting materials are provided that combine, for example, the alkali metal and halide together, or the metal and the phosphate. Thus for example, lithium, sodium, or potassium fluoride may be combined with a metal phosphate such as vanadium phosphate or chromium phosphate, or with a mixture of metal compounds such as a metal phosphate and a metal hydroxide. In one embodiment, a starting material is provided that contains alkali metal, metal, and phosphate. There is complete flexibility to select starting materials containing any of the components of alkali metal A, metal M, phosphate (or other XY₄ moiety), and halide/hydroxide Z, depending on availability. Combinations of starting materials providing each of the components may also be used.

In general, any anion may be combined with the alkali metal cation to provide the alkali metal source starting material, or with the metal M cation to provide the metal M starting material. Likewise, any cation may be combined with the halide or hydroxide anion to provide the source of Z component starting material, and any cation may be used as counter ion to the phosphate or similar XY₄ component. It is preferred, however, to select starting materials with counter ions that give rise to volatile by-products. Thus, it is desirable to choose ammonium salts, carbonates, oxides, hydroxides, and the like where possible. Starting materials with these counter ions tend to form volatile by-products such as water, ammonia, and carbon dioxide, which can be readily removed from the reaction mixture. In a preferred embodiment, lithium carbonate, ferric oxide, phosphoric acid, magnesium hydroxide and a conductive carbon are dispersed and mixed in water to prepare a slurry. The slurry is subsequently spray dried to form a powder mixture (precursor composition).

As noted above, the slurries of the invention also contain a carbonaceous compound. It is possible to use soluble carbonaceous compounds such as without limitation glycerol, starch, and a variety of sugars. Many useful carbonaceous compounds, however, are not soluble in water or other solvents. These insoluble carbonaceous materials include amorphous carbon, graphite, cokes, hydrocarbons, and the organic polymers noted above. In an alternative embodiment, effective dispersants are used along with insoluble carbonaceous material to form slurries of the invention.

Generally, dispersants are used in the invention to maintain in suspension the solid phase, which generally contains an insoluble metal compound (usually at least one insoluble transition metal compound), an insoluble carbonaceous material, or both. Suitable dispersants include those that are capable of interacting both with the liquid phase and the solid phase of the slurry to maintain a relatively stable dispersion or suspension. In general, dispersants will be those compounds or compositions having both a hydrophilic part and a hydrophobic part. Dispersants useful in industry and in forming the slurries of the invention are well known in the art and are selected from the group consisting of nonionic dispersants, anionic dispersants and cationic dispersants. Such materials are commercially available from a variety of sources.

Dispersants used in the invention are generally organic materials that can carbonize and form reducing carbon material when heated in a powdered precursor composition as discussed above. As such, they can supplement or substitute for other added sources of reducing carbon such as other organic precursor materials

The slurries of the invention are spray dried by conventional means to yield a powder precursor composition. The slurry is spray dried by atomizing the slurry to form droplets and contacting the droplets with a stream of gas at a temperature sufficient to evaporate at least a major portion by weight of the solvent used in the slurry. In one embodiment, air can be used to dry the slurries of the invention. In other embodiments, it may be preferable to use a less oxidizing or perhaps an inert gas or gas mixture. For example, an inert gas is preferred when the slurry being dried contains organic solvents. On the other hand, hot air may be suitable for drying aqueous slurries. In a preferred embodiment of the present invention, when a water based slurry is utilized hot air is used to dry the droplets. Spray drying is preferably conducted using a variety of methods that cause atomization by forcing the slurry under pressure at a high degree of spin through a small orifice, including rotary atomizers, pressure nozzles, and air (or two-fluid) atomizers. The slurry is thereby dispersed into fine droplets. It is dried by a relatively large volume of hot gases sufficient to evaporate the volatile solvent, thereby providing very fine particles of a powdered precursor composition. The particles contain the precursor starting materials intimately and essentially homogeneously mixed. The spray-dried particles appear to have the same uniform composition regardless of their size. In general, each of the particles contains all of the starting materials in the same proportion. Desirably the volatile constituent in the slurry is water. The spray drying may take place preferably in air or preferably in an inert hot gas stream. A preferred hot drying gas is argon, though other inert gases may be used. The inlet gas stream is at an elevated temperature sufficient to remove a major portion of the water with a reasonable drier volume, for a desired rate of dry powder production and particle size. Air inlet temperature, atomize droplet size, and gas flow are factors which may be varied and affect the particle size of the spray dry product and the degree of drying. There may be typically be some water or solvent left in the spray dried material. For example, there may be up to 2 - 15% by weight water. It is preferred that the drying step reduce the moisture content of the material to less than 5% by weight. The amount of solvent removed depends on the flow rate, residence time of the solvent water particles, and contact with the heated air, and also depends on the temperature of the heated air.

Techniques for spray drying are well known in the art. In a non-limiting example, spray drying is carried out in a commercially available spray dryer such as an APV-Invensys PSD52 Pilot Spray Dryer. Typical operating conditions are in the following ranges: inlet temperature 250 - 350°C; outlet temperature: 100 - 120°C; feed rate: 4 - 8 liters (slurry) per hour.

The spray dried composition is milled and compacted to form a pellet and then such pellet is sintered (heated) to effect the reaction. Thus, in a preferred embodiment, electroactive materials are prepared by heating the pellet for a time and at a temperature sufficient to form a reaction product. The reaction mixture is heated in an oven, generally at a temperature from about 400°C to about 800°C for a sufficient time and more preferably from about 550°C to about 750°C for a time from about 2 hours to about 8 hours until a reaction product forms.

The reaction is carried out with reduction in the case where the transition metal staring material is in higher oxidation state then it is in the final product. When a reduction reaction is desired the powdered precursor composition contains a carbonaceous material as discussed above. The powdered precursor composition contains a reductant that will participate in the reaction to reduce a transition metal, but that will produce by-products that will not interfere with the active material when used later in an electrode or an electrochemical cell. When the powdered precursor composition contains a reducing carbon, it is preferred to carry out the reaction in an inert atmosphere such as argon, nitrogen or carbon dioxide.

The reducing agent is generally used in excess. Any excess reducing agent does not present a problem in the active materials. The excess carbon in the reaction product does not harm the properties of the active material, because carbon is generally added to the active material to form an electrode material for use in the electrochemical cells and batteries of the invention.

The carbothermal reduction method of synthesis of mixed metal phosphates has been described in PCT Publication WO/01/53198, Barker et al., incorporated by reference herein. The carbothermal method may be used to react starting materials in the presence of reducing carbon to form a variety of products. The carbon functions to reduce a metal ion in the starting material metal M source. The reducing carbon, for example in the form of elemental carbon powder, is mixed with the other starting materials in the preparation of slurries of the invention, as discussed above. For best results, the temperature should be about 400°C or greater, and up to about 950°C. Higher temperatures may be used, but are usually not required.

The present invention also provides electrodes comprising an electrode active material made by the process of the present invention. In a preferred embodiment, the electrodes of the present invention comprise an electrode active material made by the process of this invention, a binder; and an electrically conductive carbonaceous material.

In a preferred embodiment, the electrodes of this invention comprise:

(a) from about 25% to about 95%, more preferably from about 50%> to about 90%>, electroactive material;

(b) from about 2% to about 95% electrically conductive material (e.g., carbon black); and

(c) from about 3% to about 20% binder chosen to hold all particulate materials in contact with one another without degrading ionic conductivity.

(Unless stated otherwise, all percentages herein are by weight.) Cathodes of this invention preferably comprise from about 50% to about 90% of electroactive material, about 5% to about 30% of the electrically conductive material, and the balance comprising binder. Anodes of this invention preferably comprise from about 50% to about 98% by weight of the electrically conductive material (e.g., a preferred graphite), with the balance comprising binder.

Electrically conductive materials among those useful herein include carbon black, graphite, powdered nickel, metal particles, conductive polymers (e.g., characterized by a conjugated network of double bonds like polypyrrole and polyacetylene), and mixtures thereof. Binders useful herein preferably comprise a polymeric material and extractable plasticizer suitable for forming a bound porous composite.

In a preferred process for making an electrode, the electrode active material is mixed into a slurry with a polymeric binder compound, a solvent, a plasticizer, and optionally the electroconductive material. The active material slurry is appropriately agitated, and then thinly applied to a substrate via a doctor blade. The substrate can be a removable substrate or a functional substrate, such as a current collector (for example, a metallic grid or mesh layer) attached to one side of the electrode film. In one embodiment, heat or radiation is applied to evaporate the solvent from the electrode film, leaving a solid residue. The electrode film is further consolidated, where heat and pressure are applied to the film to sinter and calendar it. In another embodiment, the film may be air-dried at moderate temperature to yield self- supporting films of copolymer composition. If the substrate is of a removable type it is removed from the electrode film, and further laminated to a current collector. With either type of substrate it may be necessary to extract the remaining plasticizer prior to incorporation into the battery cell.

Batteries:

The batteries of the present invention comprise:

(a) a first electrode comprising an electroactive material of the present invention;

(b) a second electrode which is a counter-electrode to said first electrode; and

(c) an electrolyte between said electrodes.

The electrode active material of this invention may comprise the anode, the cathode, or both. Preferably, the electrode active material comprises the cathode.

The active material of the second, counter-electrode is any material compatible with the electrode active material of this invention. In embodiments where the electrode active material comprises the cathode, the anode may comprise any of a variety of compatible anodic materials well known in the art, including lithium, lithium alloys, such as alloys of lithium with aluminum, mercury, manganese, iron, zinc, and intercalation based anodes such as those employing carbon, tungsten oxides, and mixtures thereof. In a non-limiting preferred embodiment, the anode comprises:

(a) from about 0% to about 95%, preferably from about 25% to about 95%, more preferably from about 50% to about 90%, of an insertion material;

The batteries of this invention also comprise a suitable electrolyte that provides a physical separation but allows transfer of ions between the cathode and anode. The electrolyte is preferably a material that exhibits high ionic conductivity, as well as having insular properties to prevent self-discharging during storage. The electrolyte can be either a liquid or a solid. A liquid electrolyte contains comprises a solvent and an alkali metal salt that together form an ionically conducting liquid. So called "solid electrolytes" contain in addition a matrix material that is used to separate the electrodes.

The following non-limiting examples illustrate the compositions and methods of the present invention.

EXAMPLE 1

Preparation of LiFeo. 5Mgo.osP04

(1) L1₂CO₃, Mg(OH)₂, Fe₂03, phosphoric acid and Carbon Super P milled were mixed in water to form a slurry.

1 mol L1₂CO₃ is equivalent to 73.89 g

0.95 mol Fe₂0₃ is equivalent to 151.70 g

2 mol H₃PO₄ is equivalent to 195.99 g (Phosphoric acid 85wt% is 230.58 g) O. lmol Mg(OH)₂ is equivalent to 5.83 g

0.475 mol Carbon Super P is equivalent to 5.71 g

An excess of carbon—typically 0-500%) mass excess may be used.

DI (deionized) water is 770 g

The above materials were milled and mixed in water to form a slurry.

(2) The slurry was then spray dried. Figure 2 shows the SEM photo of spray dried composition. (3) The spray dried composition was the subjected to jet milling. Figure 3 shows the SEM photo of the jet milled product.

(4) The milled product was then pelletized.

(5) The pellet was subjected to heating at 750°C for 4 hours.

(6) The pellet was then jaw crushed and pulverized or jet milled. Figure 4 shows the SEM photo of the pulverized product.

(7) The material obtained was gathered to 40 kg. The 40 kg powder was subjected to mechanofusion using an AMS-60 mixer commercially available from Hosokawa Micron Corporation. The press head was set at SS/5mm. Scraper WC/lmm. Water cooling at 80 (1/min). Purge gas - none. The revolution speed was set at 1091 rpm and mechanofusion processing continued for 30 minutes. 38 kg of mechano fused powder was recovered. Figure 5 shows the SEM photo of mechanofused powder.

The finished product had a bulk density of 0.86g/ml. and a tap density ofhe finished product had an average particle size (D50) of 4.869 microns.

EXAMPLE 2

Preparation of LiFeo. 5Mgo.osP04

(1) L1₂CO₃, Mg(OH)₂, Fe₂0₃, phosphoric acid and Carbon Super P were milled and mixed in water to form a slurry.

200 mol L1₂CO₃ is equivalent to 14.78 kg

190 mol Fe₂03 is equivalent to 30.34 kg

400 mol H₃PO₄ is equivalent to 39.20 kg (Phosphoric acid 85wt% is 46.12 kg)

20 mol Mg(OH)₂ is equivalent to 1.17 kg

95 mol Carbon Super P is equivalent to 1.14 kg

An excess of carbon—typically 0-500% mass excess may be used.

DI water is 154kg

The above materials were milled and mixed in water to form a slurry.

(2) The slurry was then spray dried.

(3) The spray dried composition was the subjected to jet milling.

(4) The milled product was then pelletized.

(5) The pellet was subjected to heating at 750°C for 4 hours.

(6) The pellet was then jaw crushed and pulverized or jet milled. (7) The material obtained was gathered and then 40 kg powder was subjected to mechanofusion using an AMS-60 mixer commercially available from Hosokawa Micron Corporation. The press head was set at SS/5mm. Scraper WC/lmm. Water cooling at 80 (1/min). Purge gas - none. The revolution speed was set at 1091 rpm and mechanofusion processing continued for 30 minutes. 38 kg of mechano fused powder was recovered.

EXAMPLE 3

Preparation of LiFeo.95Mgo.o₃Vo.o₂P0₄

(1) Li₂C0₃, Mg(OH)₂, Fe₂0₃, NH₄V0₃, phosphoric acid and Carbon Super P were milled and mixed in water to form a slurry.

200 mol Li₂C0₃ is equivalent to 14.78 kg

190 mol Fe₂0₃ is equivalent to 30.34 kg

400 mol H₃P0₄ is equivalent to 39.20 kg (Phosphoric acid 85wt% is 46.12 kg)

12 mol Mg(OH)₂ is equivalent to 0.70 kg

8 mol NH₄V0₃ is equivalent to 0.94 kg

101 mol Carbon Super P is equivalent to 1.21 kg

An excess of carbon—typically 0-500% mass excess may be used.

DI water is 154 kg

The above materials were milled and mixed in water to form a slurry.

(2) The slurry was then spray dried.

(3) The spray dried composition was subjected to jet milling.

(4) The milled product was then pelletized.

(5) The pellet was subjected to heating at 750°C for 4 hours.

(6) The pellet was then jaw crushed and pulverized or jet milled.

(7) The material obtained was gathered to 40 kg. The 40 kg powder was subjected to mechanofusion using an AMS-60 mixer commercially available from Hosokawa Micron Corporation. The press head was set at SS/5mm. Scraper WC/lmm. Water cooling at 80 (1/min). Purge gas - none. The revolution speed was set at 1091 rpm and mechanofusion processing continued for 30 minutes. 38 kg of mechano fused powder was recovered.

EXAMPLE 4

Preparation of LiFeo.95Vo.osP0₄ (1) L12CO3, Fe₂03, NH4VO3, phosphoric acid and Carbon Super P were milled and mixed in water to form a slurry.

200 mol L1₂CO₃ is equivalent to 14.78 kg

190 mol Fe₂0₃ is equivalent to 30.34 kg

400 mol H₃PO₄ is equivalent to 39.20 kg (Phosphoric acid 85wt% is 46.12 kg)

20 mol NH₄VO₃ is equivalent to 2.34 kg

110 mol Carbon Super P is equivalent to 1.32 kg

An excess of carbon—typically 0-500% mass excess may be used.

DI water is 154 kg

The above materials were milled and mixed in water to form a slurry.

(2) The slurry was then spray dried.

(3) The spray dried composition was subjected to jet milling.

(4) The milled product was then pelletized.

(5) The pellet was subjected to heating at 750°C for 4 hours.

(6) The pellet was then jaw crushed and pulverized or jet milled.

Claims

1. A method for making a lithium metal phosphate electroactive material comprising the steps of

measuring, dispersing and mixing a lithium compound, a phosphate compound, at least one transition metal compound and carbon and optionally a second metal compound in a solvent to form a slurry;

spray drying the slurry to form a powder mixture;

milling the spray dried powder mixture to form a milled powder; compacting the milled powder to form a compact pellet;

sintering the pellet at a temperature and for a time sufficient to form the electroactive material in its first form;

milling the electroactive material in its first form to give the electroactive material in its second form;

subjecting the electroactive material in its second form to a mechano fusion process to produce the electroactive material in its final form.

2. The method according to claim 1 wherein the lithium metal phosphate is of the nominal general formula

A_aM_b(P0₄)_cZ_d

3. The method according to claim 1 wherein the lithium metal phosphate is of the nominal general formula

Li_aM_b(P0₄)Z_d,

wherein

(a) 0.1 < a < 4;

(b) M is M']._mM"_m, where M' is at least one transition metal from Groups 4 to 11 of the Periodic Table; M" is at least one element which is from Group 2, 12, 13, or 14 of the Periodic Table, 0 < m < 1, and 1 < b < 3; and

(c) Z comprises halogen, and 0 < d < 4;

wherein M, Z, a, b, and d are selected so as to maintain electroneutrality of said compound.

4. The method according to claim 1 wherein the lithium metal phosphate is of the nominal general formula LiFe^MxPC^ wherein x is less than or equal to about 0.15 and greater than or equal to about 0.01.

5. The method according to claim 4 wherein the lithium metal phosphate is of the formula LiFe₀.95Mg₀.05PO₄, LiFe₀.9₅Vo.o5P0₄ or

6. The method according to claim one wherein the lithium compound is lithium carbonate, the phosphate compound is phosphoric acid, the transition metal compound is selected form the group consisting of ferric oxide, ammonium metavanadate or mixtures thereof and the second metal compound is magnesium hydroxide.

7. The method according to claim 1 wherein the solvent is water.

8. The method according to claim 1 wherein the milling steps are performed with a jet mill.

9. The method according to claim wherein the sintering step is performed at a temperature from about 550°C to about 750°C and for a time from about 2 hours to about 8 hours.