Two-melt chemical synthesis steps process for the preparation of phosphate-based cathode materials

Abstract

There is provided a two-melt chemical synthesis steps process for the preparation of a lithium metal phosphate (LiMPO4) cathode material, wherein the metal (M) is iron and / or manganese. The process comprises: a first step of mixing a lithium source and a phosphorus source in a first melt reactive pool at a temperature of about 650°C or more to form liquid LiPO3 (LiPO3(l)); and a second step of contacting the LiPO3(l) with a 'metal-oxygen' source ('M-O' source) to form LiMPO4 in a second melt reactive pool held at a temperature above the melting point of LiMPO4. Metallic iron and / or metallic manganese may be used as sole metal sources and heat from the Joule effect produced may constitute a further heating means for the pool.

Description

TITLE OF THE INVENTION TWO-MELT CHEMICAL SYNTHESIS STEPS PROCESS FOR THE PREPARATION OF PHOSPHATE-BASED CATHODE MATERIALS FIELD OF THE INVENTION

[0001] The present invention relates generally to melt processes for the preparation of lithium metal phosphate (LiMPO4) cathode materials, wherein M is iron and / or manganese. More specifically, the invention relates to such a process which comprises two melt chemical synthesis steps. Metallic iron and / or metallic manganese may be used as sole metal sources and heat from the Joule effect produced may constitute a further heating means for the pool. A cathode material according to the invention may be lithium iron phosphate (LFP; LiFePO4), lithium manganese phosphate (LiMnPO4), or lithium manganese iron phosphate (LMFP; LiMnFePO4). BACKGROUND OF THE INVENTION

[0002] Phosphate-based cathodes are currently the main type of cathodes used in lithium batteries for large-scale accumulators such as in Electric Vehicles (EVs) and grid storage. Mostly, LiFePO4(LFP) is used, but also more recently LiMnxFe(1-x)PO4(LMFP), richer in manganese.

[0003] Despite a somewhat lower energy density at the cell level, the technology around phosphate-based cathodes technology had prevailed due to the chemical stability of the P-O bond. This results in improved security making it possible to build larger cells and battery packs which are more compact and safer, and which overall achieve similar performances as batteries with cathodes having oxide cathode active material (CAM). The availability of iron and its non-toxicity vs. nickel and cobalt in industrial environment are well established. Moreover, the lower, but less aggressive voltage of the Fe+2 / Fe+3couple in the olivine structure, leads to exceptional unequalled cycle and useful life.

[0004] The challenge associated with making LFP a new energy vector capable of replacing fossil fuels, is to further reduce its precursors and processing cost to produce an electrochemically active cathode powder. Indeed, this remains the major cost contributor to the overall battery system.

[0005] Today, the worldwide production capacity of LFP exceeds 2 Mt / y, almost exclusively made in China, where solid-state synthesis process and their specific reactantshave been optimized due to the economy of scale. Such synthesis initially described in WO 2002 / 27823 A1 relies on specific high purity and fine precursors, typically Li2CO3and FePO4produced in several steps that generate important by-products with environmental impact. The use of FePO4in China is facilitated given the abundance of FeSO4waste from the country’s titanium industry. However, for most countries in the world, this is not as a viable option.

[0006] For economic and strategic considerations such as the required volumes, transportation costs, and supply security, many countries aim at developing their own production facilities. The challenge is to do so at a competitive price and within rigorous environmental regulations. There is a need for an alternative technology that can efficiently produce LFP, and that is amenable to large-scale production from low-cost reactants obtained with reasonable transformation steps in order to climb up the mineral supply chain, from the mines as well as from battery recycling.

[0007] A melt process described in WO 2005 / 062404 A1 offers this potential of simplicity and cost. It is to LFP what the blast furnace has been to iron and steel making when it replaced the solid-state reduction of iron oxide of the old bloomery furnace. This process was not optimized and scaled-up at the time since the lithium-ion battery (LIB) market was small and essentially servicing the portable electronics field which was dominated by the high-performance lithium cobalt oxide (LCO) cathodes.

[0008] When the phosphate cathode advantages started to be recognized around 2019 with the introduction of LFP specific cell and pack designs (e.g. blade cells), interest in the melt process was renewed. Such optimized processes are described is WO 2013 / 177671 A1 and WO 2015 / 179972 A1 and further optimized processed are described in WO 2024 / 148421 A1 and WO 2024 / 148427 A1. These processes address cost and productivity issues for high quality LFP / LMFP. More recently, further improvements to introduce low-cost reactants were developed by some inventors of the present application and described in WO 2024 / 1484117 A1.

[0009] There is still a need for optimized melt processes for the preparation phosphate- based cathodes. There is a need for processes that are efficient and allow for better productivity, reactants preparation and treatment, and that simplify the overall operation for low-cost high-volume production of phosphate CAM-based batteries.SUMMARY OF THE INVENTION

[0010] The inventors have designed, developed and performed a melt process for the preparation of lithium metal phosphate (LiMPO4) cathodes, wherein M is iron and / or manganese. The process comprises two melt chemical synthesis steps. Accordingly, the invention relates to a two-melt chemical synthesis steps process for the preparation of lithium iron phosphate (LFP; LiFePO4), lithium manganese phosphate (LiMnPO4), and lithium manganese iron phosphate (LMFP; LiMnFePO4). Metallic iron and / or metallic manganese may be used as sole metal sources and heat produced from the Joule effect may constitute a further heating means for the pool. Also, heat from an exothermic reaction between metallic iron and / or metallic manganese and an oxygen-containing gas used in the process may constitute yet a further heating means for the pool. The process of the invention allows for an efficient and cost-effective production of batteries comprising a phosphate cathode active material.

[0011] In embodiments of the invention, a first step of the process (Step-One) comprises forming liquid LiPO3from a lithium source and a phosphorus source, at a temperature of about 650°C or more; and a second step of the process (Step-Two) comprises contacting the liquid LiPO3with an ‘M-O’ source to form a melt composition comprising LiMPO4. The first step could also be used to prepare LiPO3 efficiently as a chemical reactant for other applications than its use in the second step. Although both chemical steps can be merged in one unique step and temperature in some modes of realization, it is more convenient to separate the two melt chemical steps to avoid interference between the precursors used and also because the conditions for first step are less demanding temperature-wise and more flexible as to melt containment and atmosphere control. Both steps can be consecutive using molten LiPO3directly for the second step or the LiPO3product solidified and stored until used for the second step.

[0012] In embodiments of the invention, the ‘M-O’ source is MnO or FeO wüstite such as that obtained according to WO 2025 / 035216 A1 and used as such in in the second step. Alternatively, an equivalent chemical composition can be obtained in-situ to form ‘M-O’ in which M is at the oxidation level of +2 by using a mixture of M0and M>+2in the proper proportions or also by using metallic M0in the melt to which an oxygen containing gas is bubbled in quantity sufficient to exothermally form the equivalent of ‘M-O’ in the melt. Combination of the ways to make the ‘M-O’ sources is also encompassed by the invention.

[0013] In embodiments of the invention, the temperature at the first step is generally and preferably between about 650°C to about 950°C; and the temperature at the second step is between about 900°C and about 1400°C, preferably between about 950°C and about 1200°C, preferably also the liquid melt is used as a reaction media for fast kinetic and heat transfer with the reactants. In some embodiments when metallic M and an oxygen containing gas are used, the temperature at first step can be the same as the temperature at the second step. It was found that when metallic sources of M are used, they could also be used in different forms (rods, plates, ingots) as electrode to generate heat using the resistivity of the liquid melt pool to contribute to the heating means by Joule effect. This variant in which the reactive pool conductivity is used with electrodes to generate heat internally can be used at either Step-One or Step-Two.

[0014] In embodiments of the invention, the process further comprises one or more of the following: bubbling buffered gas composition in the melt at the second step; in-situ analyzing the melt composition, optionally followed by a melt composition correction step; casting or atomizing from the melt composition; micronization and / or sub-micronization of LiMPO4to obtain a powder; and powder coating including by pyrolytic carbon in order to obtain an electrochemically active cathode powder.

[0015] In embodiments of the invention, the lithium source is Li2CO3, LiOH, LiNO3, Liacetate, Li3PO4, Li2SO4or a mixture thereof; and the phosphorus source is P4or its allotropes, P2O5, MAP, DAP, H3PO4, HPO3, or a mixture thereof. In other embodiments, the lithium source such as Li2SO4, Li3PO4, LiH2PO4or a mixture thereof is capable of forming the liquid LiPO3(l) with the required Li and P proportions.

[0016] In embodiments of the invention, there is provided a process of forming LiPO3(l), comprising reacting a lithium source and a phosphorus source at a temperature of about 650°C or more so that the LiPO3is liquid, preferably at a temperature between about 650°C to about 950°C. It is particularly efficient to use molten LiPO3(l) as the reaction pool to react Li and P precursors with a good kinetic and heat transfer.

[0017] In embodiments of the invention, there is provided LiPO3(l) designating LiPO3obtained efficiently by the melt process of the invention as described herein in relation to the first step. The LiPO3(l) may be in melt form, in solid form crystalline or glass to be stored, used later in the second step or as a chemical reactant for other applications.

[0018] In embodiments of the invention, there is provided a cathode material C-LiMPO4or its precursors LiPO3(l) or uncoated LiMPO4obtained by the process according to theinvention. Also, there is provided a battery comprising a cathode having the cathode material obtained by the process according to the invention. Moreover, there is provided a battery manufacturing plant embodying the process according to the invention.

[0019] The invention thus provides the following in accordance with aspects thereof: (1) A two-melt chemical synthesis steps process for the preparation of a lithium metal phosphate (LiMPO4) cathode material, wherein the metal (M) is iron and / or manganese, the process comprising: a first step of mixing a lithium source and a phosphorus source in a first melt reactive pool at a temperature of about 650°C or more to form liquid LiPO3(LiPO3(l)); and a second step of contacting the LiPO3(l) with a ‘metal-oxygen’ source (‘M- O’ source) to form LiMPO4in a second melt reactive pool held at a temperature above the melting point of LiMPO4. (2) The process according to (1) above, wherein the lithium source and the phosphorus source at the first step are mixed at desired proportions and the LiPO3(l) with the ‘M-O’ source at the second step are mixed at desired proportions, independently. (3) The process according to (1) or (2) above, wherein the temperature at the first step is between about 650°C to about 950°C; and wherein the temperature at the second step is between about 900°C and about 1400°C, preferably between about 950°C and about 1200°C. (4) The process according to any one of (1) to (3) above, wherein the temperature at the first step is the same as the temperature at the second step. (5) The process according to any one of (1) to (4) above, wherein the first melt reactive pool and the second melt reactive pool are the same or a single melt reactive pool is used at the first and second steps. (6) The process according to any one of (1) to (5) above, wherein the ‘M-O’ source is selected from the group consisting of: the ‘M-O’ source is an M+2oxide, preferably stoichiometric; the ‘M-O’ source is formed in-situ from a mixture of M0and M>+2oxide in desired proportions; the ‘M-O’ source is formed in-situ from a source of metal (M0) and an oxygen-containing gas injected in the pool; the ‘M-O’ source is MnO or FeO wüstite formedin-situ and present in the pool as a solid or as an equivalent chemical composition; and combinations thereof. (7) The process according to (6) above, wherein the source of M0is iron powder, plate, rod, or ingot; optionally the source of M0is Fe0in a melt form including an Fe-C or FexP composition and constitutes a further liquid layer in the pool. (8) The process according to (6) or (7) above, wherein the oxygen-containing gas includes pure O2, O2-enriched air, air, mixture of CO / CO2and H2 / H2O buffered gas, or a combination thereof; optionally the oxygen-containing gas is injected into the second melt reactive pool and heat from exothermic oxidation of M0contributes to heating the pool. (9) The process according to any one of (6) to (8) above, wherein at least one Fe0and / or Mn0electrode is immersed in the second melt reactive pool or the single melt reactive pool and heat generated from the Joule effect contributes to heating the pool; optionally the electrode acts as M0reactant to form the ‘M-O’ source in the presence of the oxygen- containing gas; optionally the Fe0and / or Mn0electrode is in a form which is a rod, a plate, a solid ingot, or a liquid ingot. (10) The process according to any one of (1) to (9) above, wherein heating means at the second step comprises: resistive, inductive, direct, or indirect arc heating; heat from Joule effect; heat from exothermic oxidation; or a combination thereof. (11) The process according to any one of (1) to (10) above, further comprising one or more of the following: bubbling buffered gas composition in the second melt reactive pool to control an oxygen pressure (pO2) at equilibrium thereby fixing the M+2oxidation state; in- situ analyzing a melt composition, optionally followed by a melt composition correction step; and adding a single or combined minority substitution element of M and / or PO4in the second melt reactive pool. (12) The process according to any one of (1) to (11) above, further comprising: micronization and / or sub-micronization of the LiMPO4prepared to obtain a LiMPO4in powder form; and subjecting the LiMPO4in powder form to powder coating to obtain an electrochemically active cathode powder, optionally the powder coating process comprises a pyrolytic carbon process.(13) The process according to any one of (1) to (12) above, wherein metallic iron is used as a sole source of iron and heat produced from the associated Joule effect contributes to heating the pool. (14) A two-melt chemical synthesis steps process for the preparation of a lithium metal phosphate (LiMPO4) cathode material, wherein the metal (M) is iron and / or manganese, the process comprising: a first step of mixing a lithium source and a phosphorus source in a first melt reactive pool at a temperature of about 650°C or more to form liquid LiPO3(LiPO3(l)); and a second step of contacting the LiPO3(l) with a ‘metal-oxygen’ source (‘M- O’ source) to form LiMPO4in a second melt reactive pool held at a temperature above the melting point of LiMPO4; wherein metallic iron and / or metallic manganese is used as a single source of iron and / or manganese in the process, an oxygen-containing gas is used at the second step to produce the ‘M-O’ source, and in-situ heat generation occurs which contributes to heating the pool. (15) A two-melt chemical synthesis steps process for the preparation of a lithium metal phosphate (LiMPO4) cathode material, wherein the metal (M) is iron and / or manganese, the process comprising: a first step of mixing a lithium source and a phosphorus source in a first melt reactive pool at a temperature of about 650°C or more to form liquid LiPO3(LiPO3(l)); and a second step of contacting the LiPO3(l) with a ‘metal-oxygen’ source (‘M- O’ source) to form LiMPO4in a second melt reactive pool held at a temperature above the melting point of LiMPO4; wherein at least one metallic iron and / or metallic manganese electrode is immersed in the second melt reactive pool and heat from the Joule effect contributes to heating the pool; and wherein an oxygen-containing gas is injected into the second melt reactive pool and the at least one metallic iron and / or metallic manganese electrode acting as metallic iron and / or metallic manganese reactant undergoes an exothermic oxidation to form the ‘M-O’ source, and heat from the exothermic oxidation contributes to heating the pool. (16) The process according to (14) or (15) above, wherein the lithium metal phosphate (LiMPO4) cathode material is LiFePO4or LiMnxFe(1-x)PO4with x varying between 0 and 1, preferably LiMn0.75Fe0.25PO4, and the at least one metallic electrode is a metallic iron electrode. (17) A two-melt chemical synthesis steps process for the preparation of lithium iron phosphate (LiFePO4) cathode material, the process comprising: a first step of mixing alithium source and a phosphorus source in a first melt reactive pool at a temperature of about 650°C or more to form liquid LiPO3(LiPO3(l)); and a second step of contacting the LiPO3(l) with an ‘iron-oxygen’ source (‘Fe-O’ source) to form LiFePO4in a second melt reactive pool held at a temperature above the melting point of LiFePO4; wherein at least one metallic iron electrode is immersed in the second melt reactive pool and heat from the Joule effect contributes to heating the pool; and wherein an oxygen-containing gas is injected into the second melt reactive pool and the at least one iron electrode acting as metallic iron reactant undergoes an exothermic oxidation to form the ‘Fe-O’ source, and heat from the exothermic oxidation contributes to heating the pool. (18) A two-melt chemical synthesis steps process for the preparation of lithium iron phosphate cathode material of general formula LiMnxFe(1-x)PO4with x varying between 0 and 1, the process comprising: a first step of mixing a lithium source and a phosphorus source in a first melt reactive pool at a temperature of about 650°C or more to form liquid LiPO3(LiPO3(l)); and a second step of contacting the LiPO3(l) with an ‘iron-oxygen’ source (‘Fe-O’ source) and a manganese-oxygen source (‘Mn-O’ source) to form LiMnxFe(1-x)PO4in a second melt reactive pool held at a temperature above the melting point of LiMnxFe(1-x)PO4; wherein at least one metallic iron electrode is immersed in the second melt reactive pool and heat from the Joule effect contributes to heating the pool; and wherein an oxygen- containing gas is injected into the second melt reactive pool and the at least one iron electrode acting as metallic iron reactant undergoes an exothermic oxidation to form the ‘Fe-O’ source, and heat from the exothermic oxidation contributes to heating the pool. (19) The process according to any one of (14) to (18) above, wherein the oxygen- containing gas includes pure O2, O2-enriched air, air, mixture of CO / CO2and H2 / H2O buffered gas, or a combination thereof, and wherein the oxygen-containing gas is injected into the second melt reactive pool. (20) The process according to any one of (14) to (19) above, wherein a single melt reactive pool is used and the metallic iron electrode is immersed in the single melt reactive pool. (21) The process according to any one of (14) to (20) above, wherein the metallic iron electrode is in a form which is a rod, a plate, a solid ingot, or a liquid ingot. (22) The process according to any one of (1) to (21) above, wherein: the lithium source is Li2CO3, LiOH, LiNO3, Li acetate, Li3PO4, Li2SO4, or a mixture thereof; preferably the lithiumsource is Li2SO4; and the phosphorus source is P4or its allotropes, P2O5, NH4H2PO4(MAP), (NH4)2HPO4(DAP), LiH2PO4, H3PO4, HPO3, or a mixture thereof; preferably the phosphorus source is NH4H2PO4; optionally a mixture including Li2SO4and Li3PO4and / or LiH2PO4is used to form the LiPO3(l); optionally a single compound constitutes the lithium source and the phosphorus source. (23) A process of forming LiPO3(l), comprising reacting a lithium source and a phosphorus source in the LiPO3-containing melt reactive pool at a temperature of about 650°C or more, preferably at a temperature between about 650°C to about 950°C; optionally the process further comprises subjecting the LiPO3(l) to a solidification process to obtain LiPO3(s) and storing the LiPO3(s). (24) LiPO3(l) obtained by the process as defined in (23) above, wherein the LiPO3is in a melt form LiPO3(l) or in a solid form LiPO3(s) suitable for temporary storage; optionally the LiPO3(l) or LiPO3(s) is subsequently used in the second step of the process as defined in any one of (1) to (20) above or in any other chemical synthesis including LiPF6electrolyte synthesis. (25) The process according to any one of (1) to (23) above, wherein, when the lithium source is Li2SO4and the phosphorus source is NH4H2PO4(MAP) or (NH4)2HPO4(DAP), by-products obtained from the first step include (NH4)2SO4and H2SO4; optionally (NH4)2SO4is used as fertilizer in the agricultural industry and H2SO4is used for mineral leaching / extraction in the mining industry. (26) A cathode material obtained by the process as defined in any one of (1) to (22) above, which is LiFePO4, LiMnPO4, or LiMnxFe(1-x)PO4with x varying between 0 and 1, preferably LiMn0.75Fe0.25PO4. (27) A cathode material obtained by the process as defined in any one of (1) to (22) above, optionally the cathode material comprises carbon coating, preferably pyrolytic carbon coating. (28) A battery having a cathode comprising the cathode material as defined in (27) above. (29) A battery manufacturing plant which embodies the process as defined in any one of (1) to (23) above.

[0020] Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of specific embodiments thereof, given by way of example only with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0022] In the appended drawings:

[0023] Figure 1: a. XRD pattern of LiPO3(l) material obtained from Example 1. The index lines corresponding to JCDPS file of LiPO3are shown; b. XRD pattern of dried solution of exhaust gas. Index lines corresponding to (NH4)2SO4and (NH4)3(SO4)(SO3OH) are displayed.

[0024] Figure 2: XRD pattern of the powder from Example 2 with indexation line corresponding to Li3PO4.

[0025] Figure 3: Obtained from Example 3. a. Picture of the glassy material obtained from Example 3; b. XRD pattern of the glassy material obtained after casting; c. Comparison of the same material after crystallization.

[0026] Figure 4: a. XRD patterns of the glassy LiPO3obtained according to Example 4 with comparison with that of unreacted Li3PO4added to LiPO3glassy powder. The index lines of Li3PO4are clearly visible with unreacted Li3PO4; b. Conversion to LiPO3as a function of the reaction time in the molten pool; c. Glassy LiPO3chips produced according to the conditions of Example 4.

[0027] Figure 5: a. XRD pattern of the material obtained in Example 5 with index lines corresponding to LiMnPO4material; b. XRD pattern of LiMn0.75Fe0.25PO4material obtained in Example 5.

[0028] Figure 6: Reaction kinetic as a function of time according to different SMD of iron oxide sources.

[0029] Figure 7: a. Mass evolution after gas switch in different atmospheres for carbonyl iron powder (unless mentioned otherwise); b. Sample temperature evolution for mixtures from Example 7.

[0030] Figure 8: a. Picture of the Al2O3crucible after the experiment described in example 8, the presence of residual material is clearly visible; b. XRD pattern of the material recovered from the crucible with indexation lines of Li3Fe2(PO4)3, Fe2O3, and LiFePO4.

[0031] Figure 9: XRD pattern of the material obtained in Example 9 with index lines corresponding to LiFePO4material and AlPO4.

[0032] Figure 10: a. Temperature profile upon addition of iron powder together with air and with addition of three Fe rods later on; b. Corresponding XRD pattern of the material cast using the conditions of Example 10.

[0033] Figure 11: a. Picture of the cast ingot after the experiment from Example 11; b. Corresponding XRD pattern of the ingot from Figure 11a together with Rietveld refinement; c. Picture comparing the iron rod before and after the experiment and showing consumption by the bath.

[0034] Figure 12: XRD pattern of the material obtained in Example 12 with indexation of LiFePO4material.

[0035] Figure 13: a. Temperature profile with and without AC current according to the conditions of Example 13; b. Electrodes after the experiment. DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0036] Before the present invention is further described, it is to be understood that the invention is not limited to the particular embodiments described below, as variations of these embodiments may be made and still fall within the scope of the appended claims. This is important since the examples described to establish the feasibility and embodiments of the invention are made using representative laboratory scale equipment that could be reproduced and optimized at the industrial scale by a skilled specialist. It is also to be understood that the terminology employed is for the purpose of describing particular embodiments; and is not intended to be limiting. Instead, the scope of the present invention will be established by the appended claims.

[0037] In order to provide a clear and consistent understanding of the terms used in the present specification, a number of definitions are provided below. Moreover, unless defined otherwise, all technical and scientific terms as used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure pertains.

[0038] Use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and / or the specification may mean “one”, but it is also consistent with the meaning of “one or more”, “at least one”, and “one or more than one”. Similarly, the word “another” may mean at least a second or more.

[0039] As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “include” and “includes”) or “containing” (and any form of containing, such as “contain” and “contains”), are inclusive or open-ended and do not exclude additional, unrecited elements or process steps.

[0040] The present invention relates to an improved melt-synthesis process for the preparation of LFP / LMFP cathode material, which comprises at least two chemical steps.

[0041] A first chemical step (Step-One) is essentially the formation of a molten LiPO3(l)reactant preferably in a reaction pool of molten LiPO3(l) at temperatures over 650°C up to the melting point of LFP / LMFP, generally about 950°C, using preferably Li2SO4and / or Li3PO4as a source of lithium. These salts or their mixtures are intermediary chemicals (available from mines or battery recycling and easily purified by crystallization / precipitation) currently used in the production of Li2CO3and LiOH to make cathode oxides or phosphates.

[0042] The second chemical step (Step-Two) is the formation of an LFP / LMFP composition (or LiMPO4) by reacting molten LiPO3(l) in a melt reaction pool with a source of ‘M-O’ to form LiMPO4at a temperature over the melt temperature of the LMP composition. ‘M-O’ being directly MnO or iron wüstite FeO or any chemical composition equivalent such as Fe0+ Fe2O3(or Fe3O4) in the required proportions to form FeO. Any chemical combinations capable to form ‘M-O’ in the melt being also contemplated by the invention (such as MnCO3).

[0043] In embodiments of the invention, one mode of in-situ formation of ‘M-O’ is the formation in the melt reaction pool of ‘M-O’ from metallic M where M is essentially Fe0orMn0reacted with an oxygen-bearing gas. Preferably the temperature for this step is chosen between 1000°C and 1400°C for optimal control of the formed liquid phases composition but could also temporarily be higher or even lower.

[0044] Several benefits from the two-steps / two-temperatures process of the present invention result from optimal conditions to form LiPO3(l) rapidly in the molten LiPO3reaction pool and from different sources at a lower temperature in the first step. Lower operating temperature results in improved energy efficiency, a wider choice of containment material, simplified heating means and atmosphere control, and also better ease to trap released gases or by-products, especially in the case where Li2SO4is used and avoids such gases to interfere and react with the components of the second step. Furthermore LiPO3(l) is stable under air in its molten state as opposed to most LiMPO4melt compositions.at the second step takes place at the higher temperature: LiPO3(l) + ‘M-O’(s) → LMPO4(l), can be only a simple addition reaction between a liquid (LiPO3(l) and a solid phase (‘M- O’(s)) with no gas formation and no redox process (e.g. Fe0+ Fe+3), the kinetic is rapid, e.g., few minutes, for high process productivity, resulting in additional efficiency in terms of energy required and longer life of the containment material, such as graphite. A variation of this second step is to use a combination of a metal and a metal oxide, e.g., Fe>+2+ Fe0in the right proportion to in-situ form ‘M- O’(s) as described in WO 2005 / 062404 A1 using iron powder and iron oxides such as hematite or magnetite. In the present invention it was shown that iron metal powder can be advantageously replaced in the second step by using lower-cost iron components directly from the steel industry such as rod, plates or electrodes, preferably suspended in the melt or alternatively by using a molten iron pool present as a second liquid phase using preferably low melting Fe-C cast iron or FexP compositions. Another variation of the second step is to use only metallic iron in solid or liquid form that is introduced with the reactant of the first step along with a forced bubbling of an oxygen containing gas, preferably air or pure oxygen to form ‘M-O’ in-situ while benefiting from internally generated heat contribution of the oxidation reaction to reduce the demand on an external heat source. This variation is derived from BOF (Basic Oxygen Furnace) currently used in steel-making process. In such case, a buffered gas composition (as described in WO 2015 / 179972 A1) may also be used during or after metal oxidation to control the M+2metal oxidation state and avoid over-oxidation or over-reduction such as Li3Fe2(PO4)3 / Fe2O3and Fe2P / Fe3C, respectively. In-situ heat generation from metal or other element oxidation isof great interest in a large-scale industrial process since reducing the need for energy transfer from the container’s walls or from arc or Joule heating (inert or reactive electrode) inside the crucible in this last case the reactive pool is used with the proper electrode design as the resistive electrolyte of the Joule effect. Optionally, elemental phosphorus (P4, white or red allotrope) or carbon could also be used in the present invention as FexP or Fe-C compounds for additional in-situ heat generation from oxidation with required melt composition adjustments. An additional benefit of such additive elements is to lower iron melting point in order to have a liquid metallic pool in the bottom of the LiPO3+LiMPO4melt composition during the synthesis. Both alternative ways to in-situ produce ‘M-O’ can be used in combination to control heat generation (from iron oxidation) and the desired iron oxidation level (Fe+2) along with the use of buffered gas composition, e.g. CO / CO2or H2 / H2O,

[0046] In all cases a rapid control of the melt composition as described in WO 2024 / 148427 A1 can be used to fix and adjust the melt stoichiometry, or partial substitution by other elements, but more importantly to control solid olivine LMP stoichiometry as well as any external secondary phases induced during solidification. Since the liquid reaction pool at Step-Two of the process of the invention is very favorable to introduce and homogenise one or more substituents for M in the ionic melt such as Mg, Ca, Al, transition metal and / or substituent to P in PO4, such as Si, B, Mo, W etc. and since an infinite number of such combinations are possible, the phosphate-based cathode material general formulation encompass all of these substituent elements as long as they are less than 5% of the main element used in order to keep a high energy content (>155mAh / g). In some possible configurations two-melt containers could be used successively for the second step, the first one to react rapidly a crude approximate composition and the second one to conduct the composition analysis and complete the correction or additions.

[0047] Although known resistive and inductive heating and graphite crucibles can be used for laboratory and commercial production, other means for heating are encompassed within the present invention such as arc furnace (indirect and direct) or by the use of immersed electrodes for Joule heating given the conductive nature of the melt reactive pools. The use of iron as electrodes is advantageous especially at the second step, since the iron electrodes that can be part or not or the reactants for the process combining Joule heating with chemical heating from the iron source chemical oxidation at the second step. In the case of iron electrode used as a source of iron, the electrodes design and immersion in the melt can be used to control the process along with supply of the oxygen source.

[0048] Internal heating of the reactive pool by such means avoids or reduces the need for rapid heat transfer through the container’s walls that are then less exposed to corrosion by the melt composition allowing even the implementation of self-crucible strategies or the use of conventional ceramic or metallic containing materials.

[0049] The invention further describes additional usual steps to make LMP solid ingot, atomized particles from the melt and comminution to sub-micron dimensions before coating for conductivity and stability allowing the products (LiPO3(l), bare LiMPO4or C- LiMPO4) from the process to be made, stored, and sold at different levels of transformation. DETAILED SPECIFICATION AND MODE OF REALIZATION

[0050] The present invention builds on previous developments to optimize a melt process to make phosphate cathode material, LiFePO4(LFP) or more generally LMP in which M is essentially Fe or Mn or both (LMFP). Previous work described the general concept of the process itself (WO 2005 / 062404 A1) followed by preferred modes of realization including the use of a reactive molten pool media (WO 2013 / 177671 A1), and the use of buffered gas composition to adjust state while avoiding over oxidized or reduced phases (WO 2015 / 179972 A1). Further building on the flexibility of a process operated under thermodynamic equilibrium conditions, new reactants and operating conditions have been disclosed and claimed in WO 2024 / 148427 A1, WO 2024 / 1484117 A1, WO 2025 / 035216 A1, and WO 2024 / 148421 A1 to address the material and process cost issues.

[0051] In order to further reduce (material, energy and process) cost and reduce its environmental impact, new simplification and optimization of the melt-synthesis are claimed. These claimed improvements simplify the process operation, improve the energy usage and further optimize reactant chemistry and cost.

[0052] Advantageously, the invention is adaptable to the use of low-cost iron sources available from steel-making in their solid form such as iron or cast iron ingots, plates, rods (possibly used as in-situ electrodes in the conductive melt) or in their liquid form such as low melting Fe-C cast iron or FexP. The invention can also use green iron precursors such as Fe0and FeO produced from mineral purification / reduction by hydrogen without carbothermal reduction.

[0053] The improvements rest on at least two-chemical process steps in order to form first a low melting temperature LiPO3(l) reactant under much less stringent operating conditions of temperature, atmosphere and containment materials than the conditions used at ahigher temperature in the second chemical step for LFP / LMFP melt synthesis, not to mention the easier management of released gases if any at a much lower temperature. Alternatively, this first step makes it possible to produce efficiently, store and use later on the LiPO3(l) reactant for the second step or for other chemical synthesis such as LiPF6electrolyte also of interest for lithium battery.

[0054] The first step of the synthesis takes place at a lower temperature and avoids exposing the reactants of LiPO3(l) to the chemical environment of the second step. In one embodiment, the first step advantageously makes use of low-cost Li2SO4and / or Li3PO4widely available from the mining or recycling industries easier to obtain by crystallization or precipitation instead of using conventional, but more transformed Li2CO3or LiOH precursors.

[0055] The second step is performed at a higher temperature in a reactive pool at which the LMP composition is molten and requires a controlled pO2atmosphere but is more prone to corrode containment vessels such as graphite that can wear out or be consumed after a while due to progressive oxidation at higher temperature. To ensure productivity and reduce energy consumption, this synthesis step should be kept as short as possible orLiPO3(l) + ‘M-O’ ^ T, pO2^ LiMPO4Eq.2 in which ‘M-O’ can be FeO wüstite, or MnO or equivalent composition such as ¼ (M0+ M3O4) in order to obtain M+2in the melt composition.

[0056] However, a feature of the present invention is the use, at the second step, of a single metallic M source in with the introduction of an gas capable to in-LiPO3(l) + Fe0+ ½O2^ T, pO2^ LiFePO4Eq.3

[0057] As of now, a metallic source, e.g. Fe0, cannot be used as a unique iron precursor since the final LiFePO4product requires Fe+2.

[0058] In one preferred mode of realization, the liquid LiPO3(l) formed in Step-One is introduced as such into the container of Step-Two to avoid a thermal cycle from room temperature. However, solidified crystalline or glassy LiPO3(l) formed at Step-One can also be solidified, stored and later used for Step-Two or for other synthesis of battery related material such as LiPF6as mentioned in US 6,656,441. Alternatively in the case of a single metallic M source used in conjunction with oxygen, the LiPO3(l) can be formed at the temperature of Step-Two and reacted immediately with in-situ formed ‘M-O’ to obtain LiMPO4as Step-Two. Description of Step-One:

[0059] US 6,656,441 describes several lithium sources: Li2O, Li2CO3, LiOH, LiNO3, that can be reacted by a solid-state reaction, at a temperature comprised between 300 and 650°C using ammonium phosphates or pyrophosphates to make solid LiPO3.

[0060] In the present invention LiPO3is formed in the liquid state, i.e., over 650°C, since liquid state and reactive pool are much more productive and the hot LiPO3(l) product can be used directly for the LMPO4melt synthesis (Step-Two), the resulting product is represented as LiPO3(l) since formed in the liquid state that could be used as a hot liquid in a preferred mode of realization of the invention, but LiPO3(l) could also be used in the solid cold state, glass or crystalline) when more convenient for LMPO4 synthesis. The liquid reactive pool is especially attractive with the present invention since it was found possible to use Li2SO4, Li3PO4, or their mixture as starting reactants to make the LiPO3(l) precursor at a low cost since these salts, familiar in the battery industry, are produced as intermediate in the production of Li2CO3from lithium minerals (spodumene or brine) or can be obtained from different spent battery (black mass) recycling processes as, Li2SO4, Li3PO4, or their mixture. In doing so, less transformation steps are needed and less wastes are formed, such as Na2SO4, when lithium sulfate is converted to Li2CO3for example.

[0061] In the present invention, these salts are directly reacted with phosphorous chemicals such as P2O5or ammonium phosphates, i.e., monoammonium phosphate (MAP), NH4H2PO4, or diammonium phosphate (DAP), (NH4)2HPO4, in a molten pool of LiPO3at a temperature over 650°C (LiPO3m.p.). Typical reactions are illustrated by:Li2SO4+ 2NH4H2PO4^ 2LiPO3(l) + 2NH3+ SO3+ 3H2O Eq.4 Li3PO4+P2O5^ 3LiPO3(l) Eq.5Li3PO4+ 2NH4H2PO4^ 3LiPO3(l) + 2NH3+ 3H2O Eq.6 Li2SO4+ P2O5^ 2 LiPO3(l) + SO3Eq.7

[0062] Depending on the conditions of operation during this step, it was found that the gases formed can be trapped in liquid form (NH3or H2SO4) or combined for example with DAP or MAP to form ammonium sulfate, (NH4)2SO4for example, a valuable product and fertilizer. Some of those techniques are familiar to the industry and are incorporated in the invention.

[0063] One benefit of the use of a low temperature at Step-One is an improved energy efficiency, a wider choice of containment materials such as ceramics, refractory or noble metals, wider range of pO2possible, including air, and easier management of evolved gases and by-products trapping.

[0064] Furthermore, since the lithium mining and recycling industries presently purify green Li2SO4in their process to produce Li2CO3or LiOH, whereas the phosphate mining industry also presently purifies green Merchant grade phosphoric acid (MGA) to obtain purified phosphoric acid PPA. It is an additional benefit of the invention to use one single purification step by precipitating Li3PO4for both Li and P green solutions in a single step given the fact that Li3PO4is an insoluble lithium salt in most of the pH-range. Such precipitation can be obtained using any impure lithium salt and an impure source of P, such as H3PO4and / or technical grade ammonium phosphates (MAP or DAP). After that, as illustrated in Eq. 4 and 5Li2SO4, Li3PO4, or their mixture can easily be converted to LiPO3(l).

[0065] When total or partial source of phosphorus is used for LiPO3synthesis, for example from Li3PO4, solid P2O5is quite convenient since available from the Thermal Process of phosphate mineral to obtain gas-phase-purified P4and then P2O5by oxidation. Direct use of P4and its allotropes, are also part of the invention if oxidized with an oxygen containing gas at Step-One or at Step-Two along with metallic iron.

[0066] For the present invention the LiPO3(l) formalism being used to designate hot liquid LiPO3or solid LiPO3from the melt at Step-One. This product LiPO3(l) when in a solid crystalline or glass form can be used as the precursor for Step-Two of the invention but also as a low cost and dry form as a precursor in other battery related products such as LiPF6electrolyte as described in US 6,656,441. The LiPO3(l) can have the exact (1-1-3) Li-P-O stoichiometry, but can also present minor deviation of the stoichiometry, e.g., whenLiPO3contains also some Li4P2O7or P2O5excess. This is important in the present invention since such a deviation of the stoichiometric LiPO3(l) composition or an excess of it will affect the melt composition at Step-Two and upon casting and LFP crystallization will result in Li-P excess of deficiency such as Li4P2O7, Li3PO4, or LiPO3generally present as a useful second phase to LFP. Description of Step-Two:

[0067] For Step-Two, the liquid melt reacting media is kept at a temperature sufficient to keep the LFP / LMFP composition in the liquid state, usually the temperature is kept between 1000°C and 1400°C although lower and higher temperatures are possible on a temporary basis to accelerate heat transfer, reaction kinetic or as a thermal buffer for example.

[0068] InLiPO3(l) + ‘M-O’ ^ (pO2, T) ^LiMPO4Eq.8 in which M is mainly iron and / or manganese and (pO2, T) is the temperature and oxygen partial pressure at which the reaction is conducted.

[0069] When M+2is iron, it is usually present as iron deficient wüstite that could be made and used as described in WO 2025 / 035216 A1 by the present inventors. However, a FeOchemical equivalent can be used, as for example Fe0 / Fe2O3 or Fe0 / Fe3O4 solid mixturesas mentioned in WO 2013 / 177671 A1. In the present invention, it was found that given the fast reaction in the reactive melt pool, iron powder are not required and can be advantageously replaced by ordinary products directly from steel-making such as ingot, rods, plates, electrodes or even by liquid iron, specially low melting Fe-C or Fe-P compositions present as a second liquid layer. For this high temperature step buffered gas composition mixtures such as CO / CO2or H2 / H2O could be used to adjust the desired iron +2 oxidation state.

[0070] However, another advantageous mode of realization of the invention is to use gaseous oxygen or oxidizing gases, including air, CO2or H2O, to form in-situ ‘M-O’ from the metallic foriron by: LiPO3(l) + Fe0+ 1 / 2O2^ pO2, T ^LiFePO4Eq.9

[0071] This in-situ formation of ‘M-O’ from metal oxidation is exothermic for O2containing gases (such as air) and contributes advantageously to the heat balance of the melt, reducing the need for external heat sources (resistive or radiative). As mentioned previously it was found that given the fast reaction in the reactive melt pool, iron powders are not required and can be advantageously replaced by products directly from steel- making such as ingot, rods, plates, electrodes or even by liquid iron, especially low melting Fe-C or Fe-P compositions present as a second liquid layer. Following the teaching of the present invention, one can take advantage of an in-situ exothermal oxidation reaction of iron to heat the melt, it is also possible to use other oxidizable reactant elements such as phosphorus (P4and its allotropes) or low melting Fe-C, phosphides (FexP) to contribute heat at Step-Two as long as the melt chemical composition is adjusted consequently.

[0072] In such a case, it is important to control the amount of oxygen used to avoid over- oxidation and / or to apply a buffered gas mixture on the melt during or following the LiMPO4synthesis to control the M+2oxidation state as described in WO 2015 / 179972 A1.

[0073] In parallel, melt composition can be monitored or adjusted directly in-situ by rapid element composition analysis as described in WO 2024 / 148427 A1. Slight excess of the LiPO3(l) phase as well as chemical additives or element of substitution in the melt composition can advantageously be induced in the liquid melt that might be expelled from the olivine structure upon solidification, such as LiPO3, Li4P2O7, or Li3PO4phases for example or forced as inclusion in the crystalline olivine structure.

[0074] For rapid kinetic, it might be advantageous to use metallic iron or metallic M in a powder form since it is easy to disperse and to react, but other metal forms are found possible including crushed cast iron, ingots, plate or platelets or even metallic rods or electrodes, allowing if needed, further optimization of the in-situ heating means. One advantageous variant made possible by the invention is to use conductive electrodes (metallic Fe0, Mn0, other metals, or graphite) immersed in the conductive reactive pool to generate internal heat by Joule effect, such electrodes being consumed by oxygen (sacrificial metal) or not if inert in the process. In another important variation of the invention molten metallic iron can also be used as a source of Fe0present as a second layer in the reactive pool, low melting compositions such as Fe-C or Fe-P are preferred to avoid too high an operating temperature at Step-Two, such a second layer being consumed by oxidation and reacted in-situ to form LiMPO4.

[0075] It is also another characteristic of the invention when using a metallic precursor that is in-situ oxidized by an oxygen containing gas, as described herein, to use optionally a single temperature for both Step-One, LiPO3(l) formation, and Step-Two, LiMPO4formation, that is to say, a temperature comprised between 1000°C and 1400°C as mentioned here above for Step-Two.

[0076] One possible source of iron can be high purity iron obtained from gaseous iron carbonyl sources, such as American Carbonyl, MicropowderTMiron, or pure electrolytic iron making it possible to achieve very pure, low silica and low copper grades of LFP / LMFP especially if in combination with a P source that is also gas purified, such P2O5obtained by the thermal process from P4oxidation as known to the industry. In such a case the Li reactant required to make pure LiFePO4will be from purified battery grade Li2CO3sources or from Li3PO4or Li2SO4obtained as per the present invention. Overall low cost resulting from the present invention facilitates the use a slightly higher cost purer ex-carbonyl or electrolytic M0source to obtain a high purity grade LFP or LMFP for maximum energy density and cycling performance or for further doping or substitution by controlled additional elements during Step-Two.

[0077] Although not the preferred mode of realization of the invention from energyconsiderations, the possibility to allow the LiPO3(l) from Step-One of the invention tosolidify in a glassy or crystalline form and be stored before its introduction at Step-Two to form LiMPO4in the melt according to Eq.8 or Eq.9 is also part of the invention. For the present invention, LiPO3(l) should mean LiPO3formed in the liquid state and used as a hot liquid directly or remelted after its solidification. Other variants of this two-step process familiar to the skilled person are included in the present invention to further optimize the conditions of operation of the overall process, including for example the use of additional containers to temporarily hold liquid LiPO3or the liquid LFP / LMFP composition during composition control, and correction before casting or atomization. When ‘M-O’ is formed in-situ by metallic M oxidation with a source of oxygen the final LMPO4composition can be monitored by chemical analysis sampling or more directly in-situ by using pO2sensors such as well-known potentiometric stabilized zirconia pO2sensor operated directly in the melt. In most cases bubbling a buffered gas mixture such as CO / CO2or H2 / H2O to avoid over-oxidized or over reduced impurities vs. desired M+2oxidation state is preferred.

[0078] It is also part of the invention to solidify said melt composition of Step-Two to obtain ingot or rapidly quenched by atomization to crystalline LiMPO4olivine structure with orwithout additional secondary phases or with one or more substitution or inclusion elements within the olivine crystalline structure.

[0079] It is also part of the invention to convert the LiMPO4olivine material by comminution and carbon coating as described in most cited references in order to obtain an electrochemically active cathode material but more generally by allowing the products (LiPO3(l), bare LiMPO4or C-LiMPO4) from the process to be made, stored and sold at different level of transformation. Examples EXAMPLE 1: Synthesis of liquid LiPO3(l) from Li2SO4+ NH4H2PO4(monoammonium phosphate; MAP) via molten preparation as Step-One for LFP synthesis

[0080] In this example, 5.5 g of pure anhydrous Li2SO4and 11.5 g of pure MAP (NH4H2PO4) are introduced in a graphite crucible inside a vertical tube furnace under N2flow. The crucible is heated to 700°C for 1 hour while the exhaust gas is bubbling in a water trap for further analysis. After slow cool down, still under N2, the crucible is recovered. The material is crushed, sieved to -45 µm (below 45 µm) and an XRD pattern is recorded. Figure 1a confirms the formation of LiPO3without any visible traces of sulfur impurities by XRD. LECO analysis confirmed that less than 0.2% of sulfur remains in the final material. The solution collected from the exhaust water trap is dried at 120°C overnight and the resulting powder is recovered and analyzed by XRD. Figure 1b shows the pattern of the powder from exhaust gas. Analysis confirms the formation of (NH4)2SO4along with a material with composition close to (NH4)3(SO4)(SO3OH).

[0081] This non-ideal case confirms the conversion of Li2SO4+ 2NH4H2PO4to 2LiPO3(l) + (NH4)2SO4. While LiPO3(l) can be used as a precursor for the synthesis of LiFePO4, (NH4)2SO4can be sold as a fertilizer. This is a lab simulation of the process that could advantageously be derived from this example in which a pool of LiPO3(l) at a similar temperature could be used as a reactive media for rapid reaction and improved heat transfer. It must be noted that the same conversion occurs when using hydrated lithium sulphate, Li2SO4·H2O.

[0082] This example shows that low-cost intermediates, generated during the mining or recycling industry production of Li2CO3or LiOH, conventional reactants for cathode making, can be used directly in a melt process to form LiPO3(l), a suitable Step-One intermediate for LFP / LMFP synthesis, and that sulfur gases released can be trapped toobtain value-added by-products (fertilizers) when combined with NH3releasing species (MAP), or if not, trapped as H2SO4, widely used for mineral leaching / extraction. The skilled person will be able to adapt the origin of the source of NH3, which could alternatively be coming from ammonia water as alternative to MAP or (NH4)2HPO4(diammonium phosphate; DAP). EXAMPLE 2: Synthesis of pure Li3PO4from green Li2SO4and green phosphoric acid (aka merchant grade acid, MGA) as a first step for the preparation of LiPO3(l) or LFP / LMFP

[0083] The interest of using both green Li2SO4and green H3PO4to precipitate pure Li3PO4in a single purification step is to avoid the dual purifications sequence practiced in the industry to obtain pure Li2CO3or LiOH and purified H3PO4(PPA) respectively. Li3PO4being a source of Li and a partial source of P usable as such as a reactant for the melt- synthesis of LFP / LMFP or the preparation of LiPO3(l).

[0084] In this example, pure Li3PO4is first synthesized from green Li2SO4and MGA, a green H3PO4. The green Li2SO4is mostly composed of 22,000 mg / L Li with major impurities of Ca (430 ppm), Mg (175 ppm), Mn (170 ppm) and Al (30 ppm) and originates from the supply chain of Li2CO3 / LiOH out of spodumene, but alternatively could come from the recycling of spent batteries. MGA is taken out of the supply chain of purified phosphoric acid from Apatite mines. MGA, typically destined for fertilizer preparation, is composed of 54.6% P2O5with major impurities of SO3(9,940 ppm), Fe (6,370 ppm), F (4,230 ppm), Mg (4,432 ppm), Ti (2,170 ppm) Al (1,051 ppm), Si, Ca, Na all below 500 ppm.

[0085] 5 g of green or impure Li2SO4·H2O is dissolved in 25 g of H2O and then 2.6 mL of the MGA is added with stirring. The solution is then heated to 70°C. After a few minutes of stirring, 8 mL of ammonia water 30% (NH4OH) is added to the solution in order to increase the pH and induce Li3PO4precipitation. A white precipitate forms within seconds. The precipitate is then filtered and washed 3 times before being dried at 120°C overnight. A white powder is collected out of the filter and analyzed by XRD. The pattern shown in Figure 2 confirms the formation of Li3PO4crystalline material. ICP-MS measurements performed on the white powder is detailed in Table 2. Purification of the material is evidenced as the purity is determined greater than 99%.

[0086] The same experiment performed at room temperature led to the same Li3PO4material, but less crystalline.

[0087] The filtered solution is also dried at 120°C separately and analyzed by XRD. The pattern confirms the formation of (NH4)2SO4and (NH4)3(SO4)(SO3OH) similarly to that from Figure 1b. Other traces elements cannot be evidenced by XRD due to their low concentrations.

[0088] This non-ideal case, without optimization regarding the reaction yield, demonstrates the formation of pure Li3PO4with use of MGA and green Li2SO4with formation of green (NH4)2SO4by-product. This is of importance in the mining and recycling industries as this approach eliminates production steps and their associated energy, chemical and water uses, e.g., cost, not only for lithium supply chain, without the need to use pure Li2SO4or to prepare Li2CO3or LiOH, but also for phosphate supply chain, without the need to use purified phosphoric acid (PPA). Also of importance is the formation of value added by-products for the fertilizer industry. When reproducing this example at the industrial scale, it might be useful to make a selective Li3PO4precipitation to eliminate other contaminants by well-known pH control techniques, however it is important to note that for the melt process Li2SO4and FeSO4can be tolerated as contaminant in the Li3PO4as presented in WO 2024 / 148417 A1. Table 2. Composition from ICP-MS of the solution of digested Li3PO4material from Example 2 AnLiPSCMFeAl 6.34Ti 10.02EXAMPLE 3: Synthesis of liquid LiPO3(l) from pure Li3PO4of Example 2 according to Step-One via dry (3a) and wet (3b) approaches

[0089] In Example 3a, 13.48 g of Li3PO4, as prepared in Example 2, is added to 16.52 g of P2O5in a graphite crucible. The crucible is heated to 800°C. After 1 hour at 800°C, the crucible is removed from the furnace and its content is cast in a graphite mould. A transparent glass is obtained as shown in Figure 3a. The glass is crushed, sieved to -45µm and an XRD pattern is recorded. Part of the material is further crystallized at 480°C for 5 hours. Figure 3b shows the resulting pattern of the material after casting that presents the diffuse line of a glassy material and no trace of the starting materials with comparison of the same material after crystallization in Figure 3c, similar to that in Figure 1a, confirms the formation of LiPO3without any trace impurities related to the starting materials.

[0090] In Example 3b, 13.48 g of pure Li3PO4, as prepared in Example 2, is added to 26.8 g of PPA (85% H3PO4, Sigma Aldrich). The mixture is added into a graphite crucible and introduced into the furnace heated from room temperature to 800°C at a rate of 5°C / min with a 15-minutes hold every 50°C between 100 and 350°C to ensure no boil-over or foaming. The following steps follow those of example 3a. A glassy material is obtained upon cooling and after recrystallization the XRD confirms a pure LiPO3(l). EXAMPLE 4: Fast synthesis of LiPO3(l) from Li3PO4+ P2O5using a pool of molten LiPO3(l)

[0091] In this example, a pool of 24.5 g of molten LiPO3(l), as obtained from Example 1, is kept at 800°C in a graphite crucible to evidence the fast kinetic of LiPO3formation using Li3PO4and P2O5precursors in these conditions. 4.70 g of Li3PO4, as prepared in Example 2, is mixed with 5.77 g of P2O5. The precursors are used as is without any prior deagglomeration or mechanical particle size reduction. The mixture of ca. 10.5 g is then added to the molten bath. Following the solid mixture addition, the crucible is held at temperature without any stirring for a time ranging from 2 to 10 minutes. Then the contents of the crucible are cast into a graphite mould. For each case between 2 and 10 minutes, a glassy and transparent material is obtained similarly to that in Figure 3a.

[0092] The material is ground and sieved to -45 µm for XRD analysis. Part of the -45 µm material is further crystallized at 480°C for 5 hours and analyzed by XRD. Independently of the reaction time, the XRD patterns of the glassy and crystalline materials are the same as that presented in Figure 3b and 3c, respectively. The glassy material only shows a diffuse line without any peak corresponding to starting reactants. After crystallization, only peaks related to LiPO3material are observed as those shown in Figure 3d. Figure 4a compares the pattern of the glassy material after 2 minutes reaction in the molten pool with a sample where the same amount of Li3PO4is added to glassy LiPO3powder. In this latter case, sharp peaks of Li3PO4are visible whereas when the reaction has occurred onlya diffuse line is observed. Figure 4b reports the % conversion into LiPO3of the molten media as a function of the reaction time at 800oC.

[0093] This example, with the formation of pure LiPO3from Li3PO4+ P2O5within less than 2 minutes after their introduction in a molten LiPO3(l) pool, confirms the fast reaction kinetic for the formation of LiPO3for industrial application. Owing to the fast production of LiPO3(l), the skilled person will understand that stable and cooled glassy LiPO3from LiPO3(l) can be used as a means for temporarily storing the precursor as chips as presented in Figure 4c. EXAMPLE 5: a) Synthesis according to Step-One and Step-Two of LiMnPO4by MnO and b) Synthesis according to Step-Two of LiMn0.75Fe0.25PO4from MnO and Fe / Fe2O3by its addition to liquid LiPO3(l) previously done by Li3PO4+P2O5(lab simplification, two steps in the same container at 700°C and 1100°C)

[0094] In Example 5a, approximately 19.2 g of liquid LiPO3(l) is prepared according to the procedure described in Example 3a (8.61 g of Li3PO4and 10.55 g of P2O5) are held at 800°C for 2 hours. After this time, rather than casting the molten LiPO3(l), as in Example 3a, the crucible is transferred into a second furnace held at 1100°C. After 1 hour at 1100°C, 15.6 g of MnO (Sigma Aldrich) is added to the molten LiPO3(l) and the crucible returned to the furnace and held at 1100°C for 1 hour. The molten material is then cast into a graphite mould and held under N2atmosphere until below 150°C. The ingot is then hand ground to -45 µm particles. XRD analysis of the powder confirms the production of a high purity LiMnPO4as shown in Figure 5a.

[0095] Example 5b follows the procedure of Example 5a, but rather than adding MnO, a mixture of MnO (11.9 g, Sigma Aldrich), Fe0(1.04 g, Atomet 1001HP Rio Tinto) and Fe2O3(3.97 g, ARO ArcelorMittal-Dofaco) is added. After 1 hour at 1100°C, the melt is cast in a graphite mould and cooled down under nitrogen atmosphere. The ingot is then hand ground to -45 µm particles. XRD analysis of the powder combined with pattern matching confirms the production of a high purity LiMn0.75Fe0.25PO4as presented in Figure 5b. EXAMPLE 6: Synthesis according to Step-One and Step-Two of Li Mn0.75Fe0.25PO4from Fe / Fe2O3and LiPO3(l) into a molten pool of LiMnPO4

[0096] Example 6a follows the procedure of Example 3a for the preparation of LiPO3(l). LiPO3(l) is held at 800oC for 2 hours. Meanwhile, a pool of 30 g of molten LiMnPO4is held at 1100oC. 5.5 g of LiPO3(l) is added to the molten LiMnPO4pool. 15 minutes after that,Fe0(1.18 g, Atomet 1001HP Rio Tinto) and Fe2O3(3.45 g, ARO ArcelorMittal-Dofaco). After 1 hour at 1100°C without stirring, the melt is cast in a graphite mould and cooled down under nitrogen atmosphere. The ingot is then hand ground to -45 µm particles. XRD pattern analysis of the resulting powder confirms the production of a high purity LiMnxFe(1-x)PO4compound whose lattice parameters, determined by pattern matching, match with that of LiMn0.75Fe0.25PO4shown in Figure 5b of Example 5b.

[0097] In Example 6b, to further evidence the benefit of the current approach, the same procedure was applied using different particle sizes of the Fe oxides sources, whose average particle size (Sauter mean diameter) ranged from 8 µm to +504 µm, while the same metal Fe with a average particle size of 60 µm is added to balance the charges. The final targeted composition LiMn0.75Fe0.25PO4remains the same. However, in the example, instead of leaving the crucible for 1 hour without stirring in the furnace after addition of the iron sources, the crucible is removed for casting at specific times ranging between 2 and 30 minutes. After cooling down the ingot, it is hand ground to -45 µm particles and the resulting XRD pattern is analyzed. Pattern matching is performed for each material in order to determine the lattice parameter of the LiMnxFe(1-x)PO4resulting phase. On the basis of Vegard’s law, the deviation to the targeted composition is calculated and the %Fe in the phase determined so to estimate the advancement of the reaction as a function of the starting the Fe oxide average particle size. Figure 6 presents such advancement of the reaction. The reaction occurs within minutes after addition of the transition metals in the molten media even with addition of Fe oxide source up to an impressive +500 µm. This demonstrates the efficiency of the approach for which it is still possible to synthesize Olivine materials within less than one hour despite the use of coarse transition metals sources in the molten bath.

[0098] The skilled person will understand that progressive addition of cold component into the molten bath is a preferred mode of operation in order to limit the temperature drop of the molten pool. Stirring using reactive (for instance Fe or carbon rod) or inert rod will also increase the kinetic of the advancement of reaction. In addition, the skilled person will understand that instead of using Atomet 1001HP from Rio Tinto and ARO from ArcelorMittal-DOFASCO, other grades of Fe sources are possible. These include but are not limited to metal / oxide powders such as carbonyl iron powders, atomized or atomized- reduced iron, electrolytic flakes / powders, rods, electrodes, slabs, wire coils, and foils, or mixture of these.EXAMPLE 7: DSC / TGA of in-situ oxidation of metallic Fe within a bath of liquid LiPO3(l) by gas

[0099] A mixture of LiPO3(l), obtained in a manner similar to that described in Example 4, is mixed with a source of metallic Fe, in a stoichiometric ratio required to form LiFePO4. The sources of iron considered are either carbonyl iron powder S-1100 from American Carbonyl (~97% Fe, particle size 5-10 µm) or Atomet 1001HP from Rio Tinto (~ 99% Fe, particle size of ~60 µm). The solid mixture is introduced in the DSC crucible with a weight ranging from 30-35 mg. After stabilizing at 50°C, the mixture is heated under nitrogen flow at a rate of 10°C / min up to 1000°C, and allowed to stabilise for 5 minutes. At 1000°C, LiPO3is in the liquid phase and metallic iron dispersed / partly settled. The nitrogen gas is then switched to a reaction gas (as specified in the figure caption) and held isothermally for a duration of 15 minutes. The gas is then switched back to nitrogen and allowed to settle for 1 minute before cooling down.

[0100] The results from the DSC / TGA in Figure 7a show the mass gain relative to the starting mass. For the iron carbonyl powder, the reaction is near complete with O2and air, while being very limited for the CO / CO2mixture at 1 / 1 molar ratio. For N2, the reaction does not progress. When using the coarser Atomet 1001HP powder, the reaction with O2is slower than observed for the fine carbonyl powder. The mass gain coincides with the achievement of an average Fe2+composition when reaching 111.3%, respectively after 5 and 8 minutes for the carbonyl iron powder with O2and air, and after 15 minutes for Atomet 1001HP with O2.

[0101] In Figure 7b, the sample temperature profile during the oxidation period is presented. When only nitrogen is blown all along the experiment, the signal is flat indicating no exothermic nor endothermic reaction occurred. When air or O2are used, the exothermal reactions are observed, confirming the impact of the O2and air as a means to supply energy to the system through oxidation of the metallic iron. As for the CO / CO2mixture, the reaction appears slightly endothermic, as expected. The product collected after cooling is examined and signs of over oxidation are observed by a red coloration of the collected material.

[0102] This example aims at demonstrating at lab-scale the thermal benefit of oxidizing the single Fe source within the molten mixture of LiPO3(l) + Fe0. While the amount of reacting gas is not controlled in the present non-optimized case, the skilled person will understand the implication at larger scale where the amount of oxidant, usingmass flowmeters (Coriolis, thermal mass, etc.) can easily be controlled so that Fe0can be accurately turned into Fe2+, the chemical state of iron within LiFePO4. EXAMPLE 8: Synthesis of LiFePO4made from liquid LiPO3(l) + Fe + O2without final atmosphere correction

[0103] Approximately 20.45 g of LiPO3(l), produced according to Example 3a, solidified, then broken into 1 mm pieces, is placed in an alumina crucible. The crucible is heated in a muffle furnace equipped on top with an alumina gas injection tube that penetrated the charge and is expected to remain submerged once melting occurs. A second larger alumina tube that remains above the charge or melt is used to feed new powder material, i.e., Fe source, inside the crucible without opening the furnace.

[0104] The mixture is first heated under nitrogen, fed through the gas injection tube, until 1100°C is reached. The velocity of the injected gas is adjusted so to limit spattering of the molten media. 12.98 g of Fe (Atomet 1001HP) is added through the large alumina tube. At the same time, air is fed through the injection tube for a duration of 40 minutes, approximately corresponding to 5 times the amount of O2necessary to oxidize Fe to Fe2+. Air was then replaced by N2flow for 5 minutes and the crucible removed from the furnace for casting. In that case, it was not possible to cast as the material remained stuck in thecrucible as shown in Figure 8a. After cooling under N2 atmosphere, the crucible wasbroken in order to pick up pieces of the solidified ingot. The ingot pieces were ground to - 45 µm for XRD measurement as presented in Figure 8b. In that case, the pattern indicates that the starting Fe metal was almost completely converted into Fe3+state as Fe2O3and Li3Fe2(PO4)3. Only a small amount of LiFePO4was still observed on the pattern. No Fe metal nor Al-bearing compounds were visible on the pattern.

[0105] This example, complementing Example 7, indicates by XRD analysis that iron easily oxidizes into Fe3+and Fe2+species upon direct injection of air, and by extension of oxygen or oxygen-enriched air, directly into the molten pool. No remnants of Fe metal were found in the material after the test confirming the oxidation reaction was complete. However, it was not possible to cast the oxidized sample demonstrating the need of oxidation control in the molten pool. The measurements suggest high oxygen (air) efficiency towards forming high oxidation states of iron. EXAMPLE 9: Lab-scale validation of thermal data measurements from Example 7 and thermodynamic control of the oxidation state of the resulting LiFePO4

[0106] Approximately 5.06 g of LiPO3(l), produced according to Example 3a, solidified, then broken into 1 mm pieces is mixed with 30 g of previously synthesized LiFePO4and placed in an alumina crucible.

[0107] The crucible is heated in a muffle furnace equipped on the top with 2 thermocouples, protected with alumina sleeves so to avoid the thermocouple contacting the molten LiFePO4. A thermocouple, TC1, monitors the temperature into the material contained in the crucible. The furnace is also equipped with the same 2 alumina tubes from Example 8 to feed gasses and reacting powders.

[0108] The mixture is first heated under nitrogen through the gas injection tube until 1100°C is reached. The velocity of the injected gas is adjusted so to limit spattering of the molten media. Once the temperature of TC1 is stable at 1100°C, 3.25 g of Fe (Atomet 1001HP, Rio-Tinto) is added through the large alumina tube. At the same time, air is fed through the injection tube for a duration of 2 minutes, approximately corresponding to stoichiometric amount of O2necessary to oxidize Fe to Fe2+. As soon as room temperature is reached, Fe is added, a small temperature drop is visible, but then a quick temperature increase is noted on TC1, reaching over 25°C as a result of the heat released by oxidation of the mixture in the crucible as indicated in Figure 9a while oxidation was already confirmed in Example 8. The operation was pursued substituting the air by a flow of CO / CO2in a 1 / 1 molar ratio for 20 minutes to adjust the liquid into Fe2+state. TC1 shows then a slight temperature decrease that is illustrated in Figure 9a. Once the reaction by CO / CO2is completed, the content of the crucible is poured into a graphite mould and cooled under N2. The ingot is crushed and milled until reaching particle size -45 µm for XRD measurement. The XRD confirms the major formation of LFP with residual amounts of Li3Fe2(PO4)3, Fe2O3, Li3PO4and significant amount of AlPO4contamination from the crucible as shown in Figure 9b. As can be expected from Example 8, no trace of residual Fe metal is visible on the pattern after oxidation.

[0109] This non-optimized example confirms the thermal observation of DSC measurements from Example 7. The skilled person will understand that at such lab-scale, such temperature increase confirms exothermic benefits at larger scale as a heating means. Additionally, the CO / CO2treatment performed after Fe oxidation allowed the major formation of LFP and the possibility to cast the molten media, contrasting with Example 8 where the material could not be cast owing to the oxidation state of the material and the high melting point of Li3Fe2(PO4)3(> 1200°C). The presence of residual Fe3+species indicates that the final reduction by the buffered gas mixture was not completedbefore cast. On a larger scale synthesis, the control of the oxidation state of the material can be improved by dosing the masses of Fe to O2provided, owing to efficiency factors, as would be known to the skilled person, and further refined by picking up of a sample for analysis, whether it is elemental or structural analysis as per WO 2024 / 148427 A1 before making slight adjustments for optimal LFP ingot production. EXAMPLE 10: Lab-scale operation from Example 9, but with addition of only 2 / 3 of the target iron in the molten pool for oxidation, followed by correction using dense iron rod soaked in the pool and use of storage vessel allowing polishing of the pool.

[0110] This example is similar to Example 9, but with final step of quality control performed to induce optimal LFP structure to the ingot. 5.06 g of LiPO3(l), produced according to Example 3a, solidified, then broken into 1 mm pieces, is mixed with 30 g of previously synthesized LiFePO4and placed in an alumina crucible.

[0111] As in Example 9, the furnace is equipped with 2 feed tubes, but only one immersed thermocouple protected by an alumina sleeve that is immersed in the melt (TC1).

[0112] The mixture is first heated under nitrogen through the gas injection tube until 1100°C is reached. The velocity of the injected gas is adjusted so to limit spattering of the molten media. Once the temperature of TC1 is stable at 1100°C, 2.17g of Fe (Atomet 1001HP, Rio Tinto) is added through the large alumina tube. This amount of Fe represents only 2 / 3 of the total amount of Fe necessary to obtain an LFP composition owing to the amount of LiPO3added at start. At the same time, air is fed through the injection tube for a duration of 2 minutes, approximately corresponding to 1.5 times the amount of O2necessary to oxidize Fe to Fe2+. As in Example 9, a quick temperature increase is noted on TC1, as indicated in Figure 10a. The operation was pursued with addition of CO / CO2correction in a 1.5 / 1 molar ratio for 31 minutes. One minute after the beginning of CO / CO2injection, three 1 / 8’ diameter Fe rods are soaked into the melt. The aim being to further adjust the oxidation state of Fe within the melt and equilibrate the final amount of Fe in the melt from the corrosion of the Fe rods. After 30 minutes of soaking of the rods, the rods are removed, and the molten media is poured into a graphite crucible to simulate the transfer of the molten media into a storage container for sample analysis as per WO 2024 / 148427 A1. CO / CO2mixture is also blown in the graphite crucible to ensure proper atmosphere control. A few minutes after this treatment, the content of the graphite crucible is poured into a graphite mould and cooled under N2. The ingot is crushed and milled untilreaching particle size -45 µm for XRD measurement. The XRD in Figure 10b confirms the formation of pure LFP with trace amount of Li3PO4. AlPO4contamination is also observed.

[0113] This lab-scale example under non-optimized conditions aims to simulate the operations that could be performed at large-scale with not only gas control for oxidation of iron metal in powder form added to the melt followed by reduction control from gas, but also from dense iron rods and with final quality control in a second vessel allowing polishing for ideal sample composition and structure, as per WO 2024 / 148427 A1. In the present lab-scale example, most of the sample would be required to perform the analysis, in large-scale a non-significant sample of about 10-20 grams from the homogeneous liquid molten pool in the second vessel suffices for analysis. The use of dense iron rods regulating the iron content and complementing, in the final sample, the missing iron content initially added to the melt opens the doors for consideration of various configuration including shots, wires, bares, rods, wire coils, plates, etc. The skilled person will understand the similarities with actual steelmaking and glassmaking industries. EXAMPLE 11: Use of an iron rod as sole iron source in LiMnPO4pool containing extra LiPO3(l) aimed at producing a LiMnxFe(1-x)PO4.

[0114] In example 10, the iron originating from the corrosion of the dense iron rods that integrates the LiFePO4is difficult to estimate. In the present example, the same approach is used, but in the case of a LiMnPO4pool so to evidence the iron transferred from the rods to the sample.

[0115] Crucible A (graphite) contains 2.86 g of LiPO3(l) prepared as in Example 3a, using a furnace operated at 800°C. Crucible B (alumina) contains 15.7 g of molten LiMnPO4and held at 1100°C in its own furnace. An alumina tube penetrating the melt is mounted on the furnace with Crucible B, allowing for the feeding of different gases into the melt. At the start of the trial, the contents of Crucible A are poured into Crucible B, resulting in a liquid pool height of approximately 2 cm. Three 1 / 8-inch iron rods are then dipped into the molten media so that approximately 1.5 cm protrudes into the molten pool. Then air is blown into the melt for 60 minutes while the furnace is kept at 1100°C. As per WO 2024 / 148421 A1, LiMnPO4is not prone to oxidation. The oxidative gas is then replaced by a buffer gas mixture (CO / CO2) and held for 30 minutes at 1100°C to adjust the liquid into Fe2+state. The content of the crucible is then poured into a graphite mould and cooled under N2.

[0116] A picture of the cooled ingot and its cross-section is presented in Figure 11a. XRD analysis of the powdered ingot (-45 µm) is recorded and presented in Figure 11b. Only the peaks present correspond to LiMnxFe(1-x)PO4confirming the presence of iron inside the ingot. No peaks related to iron metal or oxides are observed on the pattern. Pattern matching refinement indicates a lattice volume of 299.38 Å3, corresponding to a Fe content (1-x) of 15% in LiMnxFe(1-x)PO4based on Vegard’s law. This is in agreement with the fact that the iron rods corroded after exposition to the molten media as presented in Figure 11c, indicating the corrosion of the rods and the transfer of iron from the rods to the molten media. On the basis final Fe content from XRD, approximately 1 g of iron was transferred to the melt whereas approximately 2.9 g of iron rod was submerged in the melt, while the air flow duration was sufficient to oxidize 97 g of Fe to Fe2+. This is a direct consequence of the limited oxidation tendency of LiMnPO4compounded with the low surface area provided the dense rods.

[0117] This non-optimized lab-scale example was devised to facilitate quantification of the reaction extent. It illustrates the use of iron rods as iron source for the melt synthesis of LiMnxFe(1-x)PO4with x varying between 0 and 1. While the iron rod is corroded, iron is enriched in the molten bath. As will be understood by the skilled person, other variations and combinations may be made to the various embodiments of the example as described. For instance, the dense iron rod can differ in shape (such as tubes, plates, wires, etc.), and specific surface area. One can interpret the rod as an electrode, similar to that used in an arc or electrolytic furnaces that advantageously provides heat and may corrode upon application of current. Exposure time as well as the volume of gases and their velocities can also be adjusted in order to achieve specific Fe dissolution in the molten media. The rod could also be used in such a way as to provide agitation of the molten pool for improved mass transfer rates and thermal uniformity. As in example 10, the sample could be poured into a secondary vessel for sample extraction and correction. One advantageous operation mode is the use of a Fe2+ / Fe3+sensor based on zirconia O2reference electrode. EXAMPLE 12: Example 12 follows the procedure of Example 5 and variations of Example 10 and 11, but aimed at producing a high purity LiFePO4.

[0118] In Example 12a, approximately 19.2 g of LiPO3(l) is synthesized from high purity Li3PO4from Example 2 and high purity thermal P2O5obtained from P4oxidation. A mixture of Fe0(4.1 g, carbonyl iron powder, American Carbonyl, with HNO content determined from Inert Gas Fusion) and Fe2O3obtained from the high-temperature oxidation under H2O atmosphere of same carbonyl iron powder (11.9 g, Fe2O3-ex-carbonyliron powder) is added to the pool of LiPO3(l). After 1 hour at 1100°C, the melt is cast in a graphite mould and cooled under nitrogen atmosphere. The resulting ingot is analyzed by XRD, after grinding to -45 µm particles, confirming the production of a high purity LiFePO4as shown in Figure 12. ICP-MS measurements of the material show less than 10 ppm of copper and silicon contents.

[0119] In Example 12b, approximately 19.2 g of LiPO3(l) is synthesized from high purity Li3PO4from Example 2 and high purity thermal P2O5obtained from P4oxidation, and held at 1100oC in a graphite crucible. An alumina tube penetrating the melt is mounted on the furnace and another alumina tube allows for the feeding of different gases into the melt. Fe0(12.47 g, carbonyl iron powder, American Carbonyl, with HNO content determined from Inert Gas Fusion) is added into the melt and at the same time, air is blown for 15 minutes, corresponding to 1.3 times the amount of O2necessary to oxidize Fe to Fe3+. The oxidative gas is then replaced by a buffer gas mixture (CO / CO2) 1.5:1 and held for 30 minutes at 1100°C to adjust the liquid into Fe2+state. After this treatment, the content of the graphite crucible is poured into a graphite mould and cooled under N2. The ingot is crushed and milled until reaching particle size -45 µm for XRD measurement. The XRD pattern confirms the formation of pure LFP, similarly to that in Figure 12. EXAMPLE 13: Alternative molten media heating mode using Fe electrodes and AC current.

[0120] In preceding examples, heating of the molten media of Step-Two was performed partially using the exothermic heat of a chemical reaction directly within the molten media. This was performed by contacting the melt with an oxidative gas, such as oxygen, air, CO2, or buffered gas compositions including CO, CO2, H2, H2O containing mixtures with metallic species, either iron or manganese, in different forms such as powder, rods, electrodes, slabs, wire, wire coils and foils or mixture of these. In the present case, another heating mode is illustrated by taking advantage of the use of immersed electrodes shaped Fe source and applying an AC current directly within the melt.

[0121] First the molten pool electric resistance is determined. 50 g of previously synthesized LFP is molten in a graphite crucible placed into a clay graphite crucible. Sand is used as a thermal insulator and buffer between both crucibles and the area between the graphite crucible and the clay graphite crucible is topped with insulating wool. This crucible configuration helps to minimize the heat loss rate from the molten media. The crucible system is initially held at 1100°C using a resistive muffle furnace. A thermocouple,protected by alumina sleeves is dipped in the melt to live-record the temperature. Then, two 1 mm diameter Pt wires, guided by two alumina tubes, are immersed in the melt. Both electrodes are held 1.5 cm apart and a length of 5 mm of electrode is exposed. Once the temperature on the thermocouple is stable at 1100°C, the electric resistance is determined to be 200 Ω, using a Keithley 2700 multimeter. The same measurement is also performed after stabilization of the temperature at 1000°C, in that case, the electric resistance is 400 Ω.

[0122] The presence of a limited, but non negligible electric resistance in the molten media opens the door to an alternative heating mode using the Joule effect provided by an AC source. For the next experiment, the same crucible configuration is used. The system is initially held at 1100°C in a muffle furnace with a thermocouple immersed in the molten media. Then, two Fe electrodes (2 mm diameter) protected by alumina sleeves are dipped in the molten media. The electrodes are separated of 1.5 cm and the length in the melt is 2 cm. Once the temperature measured by the thermocouple in the bath is stable at 1100°C for 30 minutes, the furnace heating is turned off and the melt allowed to cool naturally. The temperature of the media, measured by the thermocouple, decreases and after 10 minutes of natural cooling, an AC-potential is applied at the electrodes controlled through the use of a potentiostat. The potential evolved from 0V to 140 V and the resulting AC current measured by a clamp meter is determined up to 0.5 A. As the potential is applied, the melt temperature slightly increases by up to 5°C upon application of a 72 V potential and then increases abruptly after applying a 140 V potential for several seconds, gaining up to 16°C and then suddenly dropping when the AC-potential is stopped. For the sake of comparison, a blank test is performed with the same crucible configuration, but without applying potential. A clear decreasing temperature trend is observed for 30 minutes. Figure 13a compares the temperature profile from both tests. Time 0 corresponds to the moment the furnace power is turned off and it is clear that after a few seconds, the temperature of the molten bath is dropping. Both tests, strictly follow the same temperature evolution until application of AC potential after 10 minutes of cooling. When the AC potential is turned off at 15 minutes, the temperature decreases and follows a similar temperature gradient as that of the control. Before the melt freezes below 1000°C, the electrodes and the thermocouple are removed from the melt. Figure 13b shows the electrodes after the test. Despite surface alteration or frozen media stuck on the electrodes, no clear sign of electrode corrosion is observed contrasting with Example 11 when air was blown in the melt allowing Fe oxidation to FeO.

[0123] To extend the feasibility of the Joule heating mode to Step-One also, the resistance of molten LiPO3obtained from the dehydration of 50 g of LiH2PO4was determined with the same configuration. At 900°C, the resistance of LiPO3was determined to be approximately 50 kΩ, which would make it suitable for Joule heating for Step-One.

[0124] As will be understood by the skilled person, through this laboratory experiment under non-optimized conditions, the use of two immersed Fe electrodes coupled with an AC potential in order to increase or maintain a molten LFP or LMFP bath temperature is transferable at a larger scale. In-situ Joule heating is an optional heating mode that can substitute or complement typical indirect heating modes such as resistive, inductive (heating crucible rather than charge), arc, or reverberatory furnaces for Step-Two as well as Step-One. This makes easier to design self-crucible especially attractive for Step-Two. Furthermore, the skilled person will understand that other inert electrode materials, such as graphite or other non-contaminating metals could be used for heating or more advantageously as sacrificial iron or Mn when used in conjunction with an oxygen- containing source to in-situ form ‘M-O’. Combining two heating modes using the conditions of the present example with AC potential and Fe electrodes with that of Example 11 where oxidation of Fe electrodes by an oxidizing gas and their dissolution in the melt is encompassed in the present invention. Additionally, thermal regulation could be considered by adjusting the immersed length of supplied electrodes within the molten bath.

[0125] As will be understood by the skilled person, other variations and combinations may be made to the various embodiments of the invention as described herein above. Eventually, the skilled person will be able to determine how to combine and take advantage of the different heating modes and operating modes described in all of the preceding examples to ideally control and regulate continuous or batch mode operations.

[0126] While the present disclosure has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations including such departures from the present disclosure as come within known or customary practice within the art and as may be applied to the essential features hereinbefore set forth, and as follows in the scope of the appended claims. Features which are described in the context of separate aspects and embodiments of the invention may be used together and / or be interchangeable. Similarly, features described in the context of a single embodiment may also be provided separately or in any suitable sub-combination.

[0127] The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety.

[0128] The scope of the claims should not be limited by the preferred embodiments set forth herein above; but should be given the broadest interpretation consistent with the description as a whole.

Claims

CLAIMS:

1. A two-melt chemical synthesis steps process for the preparation of a lithium metal phosphate (LiMPO4) cathode material, wherein the metal (M) is iron and / or manganese, the process comprising: a first step of mixing a lithium source and a phosphorus source in a first melt reactive pool at a temperature of about 650°C or more to form liquid LiPO3(LiPO3(l)); and a second step of contacting the LiPO3(l) with a ‘metal-oxygen’ source (‘M-O’ source) to form LiMPO4in a second melt reactive pool held at a temperature above the melting point of LiMPO4.

2. The process according to claim 1, wherein the lithium source and the phosphorus source at the first step are mixed at desired proportions and the LiPO3(l) with the ‘M-O’ source at the second step are mixed at desired proportions, independently.

3. The process according to claim 1 or 2, wherein the temperature at the first step is between about 650°C to about 950°C; and wherein the temperature at the second step is between about 900°C and about 1400°C, preferably between about 950°C and about 1200°C.

4. The process according to any one of claims 1 to 3, wherein the temperature at the first step is the same as the temperature at the second step.

5. The process according to any one of claims 1 to 4, wherein the first melt reactive pool and the second melt reactive pool are the same or a single melt reactive pool is used at the first and second steps.

6. The process according to any one of claims 1 to 5, wherein the ‘M-O’ source is selected from the group consisting of: the ‘M-O’ source is an M+2oxide, preferably stoichiometric, the ‘M-O’ source is formed in-situ from a mixture of M0and M>+2oxide in desired proportions, the ‘M-O’ source is formed in-situ from a source of metal (M0) and an oxygen-containing gas injected in the pool, the ‘M-O’ source is MnO or FeO wüstite formed in-situ and present in the pool as a solid or as an equivalent chemical composition, andcombinations thereof.

7. The process according to claim 6, wherein the source of M0is iron powder, plate, rod, or ingot, optionally the source of M0is Fe0in a melt form including an Fe-C or FexP composition and constitutes a further liquid layer in the pool.

8. The process according to claim 6 or 7, wherein the oxygen-containing gas includes pure O2, O2-enriched air, air, mixture of CO / CO2and H2 / H2O buffered gas, or a combination thereof, optionally the oxygen-containing gas is injected into the second melt reactive pool and heat from exothermic oxidation of M0contributes to heating the pool.

9. The process according to any one of claims 6 to 8, wherein at least one Fe0and / or Mn0electrode is immersed in the second melt reactive pool or the single melt reactive pool and heat generated from the Joule effect contributes to heating the pool, optionally the electrode acts as M0reactant to form the ‘M-O’ source in the presence of the oxygen-containing gas, optionally the Fe0and / or Mn0electrode is in a form which is a rod, a plate, a solid ingot, or a liquid ingot.

10. The process according to any one of claims 1 to 9, wherein heating means at the second step comprises: resistive, inductive, direct, or indirect arc heating; heat from Joule effect; heat from exothermic oxidation; or a combination thereof.

11. The process according to any one of claims 1 to 10, further comprising one or more of the following: bubbling buffered gas composition in the second melt reactive pool to control an oxygen pressure (pO2) at equilibrium thereby fixing the M+2oxidation state; in-situ analyzing a melt composition, optionally followed by a melt composition correction step; and adding a single or combined minority substitution element of M and / or PO4in the second melt reactive pool.

12. The process according to any one of claims 1 to 11, further comprising:micronization and / or sub-micronization of the LiMPO4prepared to obtain a LiMPO4in powder form; and subjecting the LiMPO4in powder form to powder coating to obtain an electrochemically active cathode powder, optionally the powder coating process comprises a pyrolytic carbon process.

13. The process according to any one of claims 1 to 12, wherein metallic iron is used as a sole source of iron and heat produced from the associated Joule effect contributes to heating the pool.

14. A two-melt chemical synthesis steps process for the preparation of a lithium metal phosphate (LiMPO4) cathode material, wherein the metal (M) is iron and / or manganese, the process comprising: a first step of mixing a lithium source and a phosphorus source in a first melt reactive pool at a temperature of about 650°C or more to form liquid LiPO3(LiPO3(l)); and a second step of contacting the LiPO3(l) with a ‘metal-oxygen’ source (‘M-O’ source) to form LiMPO4in a second melt reactive pool held at a temperature above the melting point of LiMPO4, wherein metallic iron and / or metallic manganese is used as a single source of iron and / or manganese in the process, an oxygen-containing gas is used at the second step to produce the ‘M-O’ source, and in-situ heat generation occurs which contributes to heating the pool.

15. A two-melt chemical synthesis steps process for the preparation of a lithium metal phosphate (LiMPO4) cathode material, wherein the metal (M) is iron and / or manganese, the process comprising: a first step of mixing a lithium source and a phosphorus source in a first melt reactive pool at a temperature of about 650°C or more to form liquid LiPO3(LiPO3(l)); and a second step of contacting the LiPO3(l) with a ‘metal-oxygen’ source (‘M-O’ source) to form LiMPO4in a second melt reactive pool held at a temperature above the melting point of LiMPO4, wherein at least one metallic iron and / or metallic manganese electrode is immersed in the second melt reactive pool and heat from the Joule effect contributes to heating the pool, and wherein an oxygen-containing gas is injected into the second melt reactive pool and the at least one metallic iron and / or metallic manganese electrode acting as metallic ironand / or metallic manganese reactant undergoes an exothermic oxidation to form the ‘M-O’ source, and heat from the exothermic oxidation contributes to heating the pool.

16. The process according to claim 14 or 15, wherein the lithium metal phosphate (LiMPO4) cathode material is LiFePO4or LiMnxFe(1-x)PO4with x varying between 0 and 1, preferably LiMn0.75Fe0.25PO4, and the at least one metallic electrode is a metallic iron electrode.

17. A two-melt chemical synthesis steps process for the preparation of lithium iron phosphate (LiFePO4) cathode material, the process comprising: a first step of mixing a lithium source and a phosphorus source in a first melt reactive pool at a temperature of about 650°C or more to form liquid LiPO3(LiPO3(l)); and a second step of contacting the LiPO3(l) with an ‘iron-oxygen’ source (‘Fe-O’ source) to form LiFePO4in a second melt reactive pool held at a temperature above the melting point of LiFePO4, wherein at least one metallic iron electrode is immersed in the second melt reactive pool and heat from the Joule effect contributes to heating the pool, and wherein an oxygen-containing gas is injected into the second melt reactive pool and the at least one iron electrode acting as metallic iron reactant undergoes an exothermic oxidation to form the ‘Fe-O’ source, and heat from the exothermic oxidation contributes to heating the pool.

18. A two-melt chemical synthesis steps process for the preparation of lithium iron phosphate cathode material of general formula LiMnxFe(1-x)PO4with x varying between 0 and 1, the process comprising: a first step of mixing a lithium source and a phosphorus source in a first melt reactive pool at a temperature of about 650°C or more to form liquid LiPO3(LiPO3(l)); and a second step of contacting the LiPO3(l) with an ‘iron-oxygen’ source (‘Fe-O’ source) and a manganese-oxygen source (‘Mn-O’ source) to form LiMnxFe(1-x)PO4in a second melt reactive pool held at a temperature above the melting point of LiMnxFe(1-x)PO4, wherein at least one metallic iron electrode is immersed in the second melt reactive pool and heat from the Joule effect contributes to heating the pool, and wherein an oxygen-containing gas is injected into the second melt reactive pool and the at least one iron electrode acting as metallic iron reactant undergoes an exothermic oxidation to form the ‘Fe-O’ source, and heat from the exothermic oxidation contributes to heating the pool.

19. The process according to any one of claims 14 to 18, wherein the oxygen-containing gas includes pure O2, O2-enriched air, air, mixture of CO / CO2and H2 / H2O buffered gas, or a combination thereof, and wherein the oxygen-containing gas is injected into the second melt reactive pool.

20. The process according to any one of claims 14 to 19, wherein a single melt reactive pool is used and the metallic iron electrode is immersed in the single melt reactive pool.

21. The process according to any one of claims 14 to 20, wherein the metallic iron electrode is in a form which is a rod, a plate, a solid ingot, or a liquid ingot.

22. The process according to any one of claims 1 to 21, wherein:the lithium source is Li2CO3, LiOH, LiNO3, Li acetate, Li3PO4, Li2SO4, or a mixture thereof;preferably the lithium source is Li2SO4; and the phosphorus source is P4or its allotropes, P2O5, NH4H2PO4(MAP), (NH4)2HPO4(DAP), LiH2PO4, H3PO4, HPO3, or a mixture thereof; preferably the phosphorus source is NH4H2PO4, optionally a mixture including Li2SO4and Li3PO4and / or LiH2PO4is used to form the LiPO3(l), optionally a single compound constitutes the lithium source and the phosphorus source.

23. A process of forming LiPO3(l), comprising reacting a lithium source and a phosphorus source in the LiPO3-containing melt reactive pool at a temperature of about 650°C or more, preferably at a temperature between about 650°C to about 950°C, optionally the process further comprises subjecting the LiPO3(l) to a solidification process to obtain LiPO3(s) and storing the LiPO3(s).

24. LiPO3(l) obtained by the process as defined in claim 23, wherein the LiPO3is in a melt form LiPO3(l) or in a solid form LiPO3(s) suitable for temporary storage, optionally the LiPO3(l) or LiPO3(s) is subsequently used in the second step of the process as defined in any one of claims 1 to 20 or in any other chemical synthesis including LiPF6electrolyte synthesis.

25. The process according to any one of claims 1 to 23, wherein, when the lithium source is Li2SO4and the phosphorus source is NH4H2PO4(MAP) or (NH4)2HPO4(DAP), by- products obtained from the first step include (NH4)2SO4and H2SO4, optionally (NH4)2SO4is used as fertilizer in the agricultural industry and H2SO4is used for mineral leaching / extraction in the mining industry.

26. A cathode material obtained by the process as defined in any one of claims 1 to 22, which is LiFePO4, LiMnPO4, or LiMnxFe(1-x)PO4with x varying between 0 and 1, preferably LiMn0.75Fe0.25PO4.

27. A cathode material obtained by the process as defined in any one of claims 1 to 22, optionally the cathode material comprises carbon coating, preferably pyrolytic carbon coating.

28. A battery having a cathode comprising the cathode material as defined in claim 27.

29. A battery manufacturing plant which embodies the process as defined in any one of claims 1 to 23.

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