Melt process for producing crystalline olivine cathode materials from various compositional sources

Abstract

A two-stage melting process for producing a lithium metal phosphate (LiMPO4) cathode material having a specified composition is provided. The process includes first and second melting steps and an intermediate analysis step between the two melting steps. The first melting step includes mixing reactive precursors to form a first molten pool having a first molten pool composition. The second melting step includes adjusting the first molten pool composition based on results obtained from the intermediate analysis step to obtain, for example, a second molten pool having a specified composition. The reactive precursors include Li-, M-, and P-containing materials, used cathode materials from used batteries, off-spec cathode materials, and combinations thereof, where M is at least one transition metal. The second melting step and the intermediate analysis step may be repeated multiple times as necessary until the specified composition is obtained.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 479,266, filed January 10, 2023, the contents of which are incorporated herein by reference in their entirety.

[0002] The present invention generally relates to a melting process for producing cathode materials. More specifically, the present invention relates to a two-stage melting process for producing lithium metal phosphate (LiMPO4, where M is at least one transition metal) cathode materials having a defined composition. The process according to the present invention includes an intermediate step between the two melting steps. Reactants used in the process can include Li-, M-, and P-containing materials, used cathode materials from used batteries, and off-spec cathode materials from manufacturing plants. [Background technology]

[0003] Lithium metal phosphate (LiMPO4, where M is at least one transition metal) cathodes are the cathode of choice in most energy storage and electrical transport devices. In fact, LiMPO4 cathodes have excellent inherent properties, such as thermal and chemical stability and long life. The manufacturing cost of LiMPO4 cathodes is 、 In particular, since it accounts for more than 20% of the total battery manufacturing cost, it needs to be reduced as much as possible.

[0004] The production of lithium metal phosphate olivine cathode materials relies heavily on available elements such as Fe, Mn, P (as PO4), and Li (when recycled). This is advantageous for achieving the goal of reducing production costs. However, the currently used chemical precursors and the resulting LiFePO4 (LFP) and LiFe x Mn 1-xThe manufacturing process for common lithium metal phosphate cathodes, such as PO4 (LFMP), still entails high production costs. Indeed, battery-grade FePO4, LiOH, and Li2CO3 precursors must be well-defined, pure, and finely sized when used as reactants in solid-state or solvent-assisted precipitation syntheses.

[0005] Generally, in most existing solid-state and solvent-assisted precipitation syntheses described for producing electrochemically active lithium metal phosphate cathodes, the composition is tailored by controlling the chemistry, purity, and proportions of input materials, including lithium, transition metals, and phosphates ( WO 02 / 27823 A1 , WO 02 / 27824 A1 , and WO 02 / 083555 A2 ). This input control, required for solid-state synthesis and most solvent-assisted precipitation synthesis methods, has also been applied to recently disclosed melt processes ( WO 05 / 062404 A1 , WO 2013 / 177671 A1 , and WO 2015 / 179972 A1 ). However, the need for well-defined reactant compositions in predetermined proportions to control the optimal final composition is costly.

[0006] There is a need for a process that can produce lithium metal phosphate cathode materials with desired final compositions. There is a need for such a process that is efficient and cost-effective. Summary of the Invention

[0007] We have designed and developed a two-step melting process for producing LiMPO4 (where M is at least one transition metal) cathode materials with defined compositions. The process involves first and second melting steps, resulting in first and second melt pools, respectively, and an intermediate analysis step between the two melting steps. The second melting step and the intermediate analysis step can be repeated multiple times as necessary until the defined composition is achieved. The reactants used in this process can include Li-, M-, and P-containing materials, used cathode materials from used batteries, and off-spec cathode materials from manufacturing plants.

[0008] In an embodiment of the invention, the process further comprises a post-synthesis step, which involves subjecting the second molten pool to a casting, solidification, grinding process, and a coating process with an electrochemically active material.

[0009] In embodiments of the present invention, the first melt pool composition determined by the intermediate analysis step may be found to be P-deficient and / or Li-deficient and / or M-rich and / or may indicate the presence of undesired elements. The second melting step may include adding a P-containing material to the first melt pool, and / or adding a Li-containing material to the first melt pool, and / or adding an M-containing material to the first melt pool, and / or injecting a gas flow into the first melt pool, and / or extracting the undesired elements from the first melt pool. Such extraction may also be performed on the second melt pool.

[0010] In embodiments of the present invention, the reaction precursor may include used or off-spec cathode material from spent batteries. Additionally, the first melt pool composition, as determined by the intermediate analysis step, may contain undesirable elements. Therefore, the second melting step may include extracting the undesirable elements from the second melt pool. In such embodiments, prior to performing the first melting step, a preliminary step may be performed, including combusting the material to remove any carbonaceous material present in the used or off-spec cathode material.

[0011] In embodiments of the present invention, the reaction precursor may include a material containing a first metal M1 (M1-containing material), and the second melting step may include adding a material containing a second metal M2 (M2-containing material) to the first molten pool. In embodiments of the present invention, M1 may be Fe and M2 may be Mn.

[0012] In embodiments of the present invention, the intermediate analysis step to determine the first melt pool composition may include using a rapid analytical technique commonly used in the art, or a combination of these techniques, hi other embodiments, the intermediate analysis step may include using an online gas analyzer such as FTIR or MS.

[0013] In an embodiment of the present invention, there is provided a LiMPO4 cathode material obtained by the process of the present invention, which is LiFePO4, LiFe 1-x Mn x PO4 (where x varies between 1 and 0), or LiMnPO4.

[0014] In an embodiment of the present invention, a battery is provided having a cathode comprising a LiMPO4 cathode material obtained by the process of the present invention.

[0015] In an embodiment of the present invention, a cathode or battery manufacturing plant is provided that embodies the process of the present invention.

[0016] According to its aspects, the present invention provides the following. (1) A two-stage melting process for producing a lithium metal phosphate (LiMPO) cathode material having a defined composition, comprising first and second melting steps, and an intermediate analysis step between the two melting steps, wherein the first melting step comprises mixing reactive precursors to form the first molten pool having the first molten pool composition, and the second melting step comprises adjusting the first molten pool composition based on results obtained from the intermediate analysis step, e.g., to obtain a second molten pool having the defined composition, wherein the reactive precursors comprise materials selected from the group consisting of Li-, M-, P-containing materials, spent cathode materials from spent batteries, off-spec cathode materials, and combinations thereof, wherein M is at least one transition metal, and optionally the second melting step and the intermediate analysis step are repeated multiple times. (2) The process of (1) above, wherein the first melt pool composition determined by the intermediate analysis step is found to be P-deficient and / or Li-deficient and / or M-excess and / or the presence of undesired elements, and the second melting step comprises adding a P-containing material to the first melt pool, and / or adding a Li-containing material to the first melt pool, and / or adding an M-containing material to the first melt pool, and / or injecting a gas stream into the first melt pool and / or extracting the undesired elements, preferably the undesired elements are metallic elements that are thermodynamically stable at the melting temperature, more preferably the undesired elements include Cu, Ni, and / or Cr, and even more preferably the undesired elements include Cu, and preferably the gas stream comprises CO, H, N, and combinations thereof. (3) The process of (1) or (2) above, wherein the reaction precursor comprises spent cathode material from spent batteries, off-spec cathode material, or a combination thereof, the first molten pool composition determined by an intermediate analysis step comprises undesired elements, and the second melting step comprises extracting the undesired elements from the second molten pool, preferably by liquid-liquid or liquid-solid phase separation. (4) The process of (3) above, further comprising a preliminary step of combusting the material to remove carbonaceous material before carrying out the first melting step. (5) The process according to (3) or (4) above, wherein the first molten pool and the second molten pool are each independently subjected to oxidation and / or mechanical separation to remove carbonaceous material. (6) The process according to any one of (1) to (5) above, wherein the reactive precursor comprises a material containing a first metal M1 (M1-containing material), and the second melting step comprises adding a material containing a second metal M2 (M2-containing material) to the first molten pool, preferably wherein M1 is Fe and M2 is Mn. (7) The process according to any one of (1) to (6) above, wherein the first and second melting steps are carried out at a first temperature and a second temperature, respectively, under an inert and / or reducing atmosphere, and the first molten pool is maintained at the first temperature and the inert and / or reducing atmosphere during the intermediate analysis step, preferably the first and second temperatures are each independently between about 800°C and about 1300°C, more preferably above 1000°C, and preferably the inert and / or reducing atmosphere comprises the use of Ar, CO2, H2, N2, and combinations thereof. (8) The process according to any one of (1) to (7) above, further comprising a post-synthesis step. (9) The process of (8) above, wherein the first post-synthesis step comprises subjecting the second molten pool to a casting, solidification and grinding process to obtain a powdered, reduced particle size material, preferably in the micron, submicron, nano, and combinations thereof range. (10) The process of (9) above, wherein the second post-synthesis step comprises subjecting the particle size reduced material to a coating process with an electrochemically active material to obtain an electrochemically active LiMPO4 cathode material, preferably wherein the electrochemically active material comprises carbon. (11) The process according to any one of (1) to (10) above, wherein the first melting step and the second melting step are carried out in a first container and a second container, respectively, and the first container and the second container may be different or the same. (12) The process according to any one of (1) to (11) above, wherein the first melting step and the second melting step are each carried out independently using mechanical stirring and / or gas-assisted stirring of the molten pool. (13) The process according to any one of (1) to (12) above, wherein the first melting step and the second melting step each independently include phase separation or filtration of the melt. (14) The process according to any one of (1) to (13) above, wherein the metal (M) is Fe or Mn, or both Fe and Mn. (15) The process according to any one of (1) to (14) above, wherein the Li-containing material is selected from the group consisting of LiOH, Li2CO3, Li2SO4, Li3PO4, LiPO3, LiH2PO4, and combinations thereof. (16) The M-containing material is an Fe-containing material, and Fe 0 , Fe2O3, FeO, FeSO4, concentrated ores such as hematite and magnetite, and combinations thereof. (17) The M-containing material is a Mn-containing material, 0 , MnCO3, MnO2, Mn2O3, Mn3O4, MnO, MnSO4, concentrated ores such as pyrolusite, rhodochrosite, hausmannite, manganese-rich alloys such as ferromanganese (Mn+Fe), and combinations thereof. (18) The process according to any one of (1) to (17) above, wherein the phosphorus-containing material is selected from the group consisting of P2O5, Li3PO4, LiPO3, LiH2PO4, (NH4)2HPO4, (NH4)H2PO4, and combinations thereof. (19) The used or off-spec cathode material is carbon-coated LiMPO4, FePO4, Li3PO4, Li3PO4-Li2SO4 mixture, variable composition Li-FeO x and a Mn-containing compound. (20) The process according to any one of (1) to (19) above, wherein the intermediate analysis step comprises using a rapid analytical technique selected from the group consisting of electron diffraction spectroscopy (EDS), glow discharge mass spectrometry (GD-MS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), laser-induced breakdown spectrometry (LIBS), X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), inductively coupled plasma mass spectrometry (ICP-MS), microwave plasma atomic emission spectrometry (MP-AES), and combinations thereof. (21) The process according to any one of (1) to (20) above, wherein the intermediate analysis step includes determining the first melt pool composition using an online gas analyzer, preferably the online gas analyzer is FTIR or MS. (22) The process according to any one of (1) to (21) above, which is continuous or semi-continuous. (23) The manufacturing process according to any one of (1) to (22) above, wherein the LiMPO4 positive electrode material has an olivine structure. (24) The process according to any one of (1) to (23) above, wherein the LiMPO4 positive electrode material is electrochemically active, preferably the LiMPO4 positive electrode material is carbon coated. (25) A LiMPO4 positive electrode material obtained by the manufacturing process according to any one of (1) to (24) above. (26) LiFePO4, LiFe 1-x Mn xThe LiMPO4 cathode material according to (25) above, wherein x is selected from the group consisting of LiMnPO4, LiMnPO4, and LiMnPO4, wherein x varies between 1 and 0. (27) A battery in which the positive electrode contains the material defined in (25) or (26) above. (28) A positive electrode or battery manufacturing plant that embodies the process according to any one of (1) to (24) above.

[0017] Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-limiting description of specific embodiments, given by way of example only with reference to the accompanying drawings.

[0018] This patent or application 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.

[0019] In the accompanying drawings: [Brief explanation of the drawings]

[0020] [Figure 1] XRD pattern of the sample in Example 1. Traces of the Li3PO4 phase are visible in the olivine structure. [Figure 2] XRD pattern of the final sample in Example 2. Pure LiFePO4 structure is visible. [Figure 3] XRD pattern of the sample in Example 4. The LiFePO4 olivine structure is visible along with the Li3PO4 and Li4P2O7 phases. [Figure 4] XRD pattern of the sample from step 1 (from off-spec material) of Example 5 and the XRD pattern of the final step (LiFe0.5Mn0.5PO4) after correction. [Figure 5]XRD pattern of the sample from step 1 of Example 7 and the XRD pattern of the sample from the final step after correction. In step 1, a large amount of Li3PO4 is visible, but after correction in step 2, a pure olivine microstructure is found. [Figure 6] A) XRD pattern of the sample from step 1 (LiMnPO4) and the final step after adding off-spec LiFePO4 (LiFeO.25MnO.75PO4) in Example 8. B) Lattice constants after different steps (Step 1: MCDL58-S1) and after correction (i.e., addition of off-spec LiFePO4) (Step 2: MCDL58). [Figure 7a] A photo of an LFP ingot with copper droplets visible. [Figure 7b] Photographs of the LFP ingot and Ag metal ingot. Unlike Figure 7a of Example 9a, no trace of copper droplets is visible on the LFP ingot. DETAILED DESCRIPTION OF THE INVENTION

[0021] Before further describing the present invention, it is to be understood that the present invention is not limited to the specific embodiments described below, but that variations of these embodiments may be made and are within the scope of the appended claims. It is also to be understood that the terminology used herein is used to describe particular embodiments, but is not intended to be limiting. Rather, the scope of the present invention is defined by the appended claims.

[0022] In order to provide a clear and consistent understanding of the terminology used in this disclosure, some definitions are provided below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0023] The words "a" or "an," when used in conjunction with the term "comprising" in the claims and / or specification, may mean "one," but are consistent with the meanings of "one or more," "at least one," and "one or more than one." Similarly, "another" can mean at least a second, or more.

[0024] As used in this specification and claim(s), the words "comprising" (and any form of including, 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.

[0025] As used herein, the term "two-step melt process" in connection with the process of the present invention refers to a melting process for producing a LiMPO4 (where M is at least one transition metal) cathode material having a defined composition. The process includes two melting steps, identified herein as a first melting step and a second melting step, with an intermediate analysis step performed between the two melting steps. The process may also include additional steps performed after the second melting step. These additional steps are identified herein as post-synthesis steps and include processes such as casting, solidification, grinding, and coating with an electrochemically active material. The terms "two-step melt synthesis process" and "two-step synthesis" are also used herein. Therefore, the terms "two-step melt process," "two-step melt synthesis process," and "two-step synthesis" are used interchangeably.

[0026] As used herein, the term "off-spec" or its abbreviation "off-spec" refers to a product or material that does not meet a manufacturer's specifications, i.e., is unsuitable for use for its intended purpose, and is therefore discarded. For example, the term "off-spec cathode material" or "off-spec cathode material" is used herein to refer to cathode material from another factory that is deemed unsuitable for use in a battery. Such material is used in a process according to the present invention, where its composition is modified to the desired composition.

[0027] We have designed and developed a two-step melting process for producing LiMPO4 (where M is at least one transition metal) cathode materials with defined compositions. The process includes a first melting step, a second melting step, and an intermediate analysis step between the two melting steps. Each of these steps is described in detail here.

[0028] The present invention is further based on a melting process for producing LiMPO4 positive electrode compositions with an olivine structure at low cost. In this disclosure, M in LiMPO4 represents at least one transition metal. In an embodiment of the present invention, M is Fe, Mn, or both. In previous applications, it was stated that the melt synthesis method can use a wider range of chemically defined reactants than other reactant-specific LiMPO4 synthesis processes (such as solid-state synthesis methods), so long as the chemical composition is stable and known, e.g., pure Fe. 0 It has been shown that the production costs of well-defined LiMPO4 cathodes can be further optimized by using Li3PO4, Fe2O3, and even concentrated ores such as hematite and magnetite.

[0029] The present invention is based on the short reaction times possible, preferably achieved by using a stirred liquid molten reaction pool, and more importantly, the unique reversibility of the synthesis reaction at thermodynamic equilibrium, allowing the desired composition to be cast to be adjusted by modifying the composition based on rapid in situ analysis, which not only improves the reliability of the process but also optimizes yields while allowing the use of precursors with different compositions and reactants recovered from recycled spent batteries.

[0030] The present invention relates to a more flexible continuous or semi-continuous two-stage melting process for producing crystalline olivine cathode materials of well-defined composition from a broader range of reactants that are compositionally variable and can be fed directly into a first molten reaction pool as is. After the two-stage synthesis and solidification, the cathode materials have an olivine structure and a general well-defined composition, represented by LiMPO4, where M is at least one transition metal.

[0031] The two-stage melting process of the present invention is based on a first large molten reaction pool to which different Li, M, and PO4-containing sources, with variable or precisely unknown chemical compositions, are fed in their approximate LiMPO4 ratios and stirred to achieve a first compositional equilibrium. At this point, an aliquot is taken from the bath and rapidly analyzed to determine the exact melt elemental composition. Based on this analytical feedback and the known mass of the molten pool, in a second melting step, smaller amounts of chemically defined Li, M, and P reactants are added to the pool in the required amounts and stirred again until a new equilibrium is reached. This ultimately ensures that the final composition of the melt before casting and solidification matches the desired LiMPO4 composition.

[0032] Unlike currently used solid-state and precipitation syntheses of phosphate or oxide cathodes, the speed of chemical reactions in the molten state, and more importantly, their reversibility and active melt stirring, allow for such compositional corrections as long as rapid and accurate physicochemical analytical feedback is available after the first step. Therefore, in the second step, the exact optimal composition of the melt before casting and solidification can be achieved without fully defining the composition of all reactants used in the first step with high accuracy in advance through in-house analysis or composition certification by contract with materials suppliers. Given the high specific gravity of the solid and liquid reactants and the high viscosity of some reactants, stirring the melt is desirable in both steps. This ensures rapid reaction, equilibrium, and compositional reversibility of the melt (including the presence or absence of a gas phase in the stirring process). Nickel, chromium, and their alloys are thermodynamically stable under the controlled reducing conditions used in the present phosphate melt, making them suitable containment and stirring materials, replacing the more brittle and reactive graphite and most partially soluble ceramic materials. For similar reasons, copper has also been found to be stable despite being liquid above 1084°C. This property allows for the separation of ionic or metallic copper from the melt, as shown in the examples. High-density liquid copper can be innovatively separated from the melt to allow for in-situ compositional analysis between the synthesis steps of the present invention. In addition to the separation of copper from the melt, other metallic elements (e.g., Ag, Sn, Pb, Bi, etc.) that are thermodynamically stable under the reducing conditions of the process can be separated as second phases of different densities depending on their solubility in the second liquid metal phase at the melting temperature.

[0033] This represents a significant simplification and cost reduction for producing well-defined LiMPO4 cathode materials from a wide range of variable and approximate compositions of Li, M, and PO4 reactants or reactant combinations, replacing the precise quantitative measurement of well-defined reactive chemical reactants. Furthermore, this two-step melt synthesis process allows for the use of off-spec products, process by-products, and even recycled LiMPO4 cathodes from spent batteries as reactants, which can be used as reactants in the first step and then compositionally corrected in the second step. In particular, spent C-LiMPO4 cathodes can also be recovered by burning the conductive carbon and ultimately the organic cathode binder before or during step 1 of the process according to the present invention.

[0034] Additionally, in Step 2 of the synthesis, it is convenient, but not essential, to use well-defined, pure reactants with limited particle size, e.g., less than 200 μm, for compositional control, since only minor adjustments are typically required at that point to reach the desired LiMPO4 melt composition. An additional advantage of this two-stage melt synthesis process is that it allows for different temperatures, atmospheres, and containment materials when using two vessels. For example, a higher temperature in Step 1 can improve the dissolution rate of the granular reactants, and different pO2 gas atmospheres can control the stoichiometry of LiMPO4 and the oxidation state of the transition metals. As an example, if the PO4 source for producing LiFePO4 is PO5, which is particularly hygroscopic, great care must be taken to prevent moisture absorption during reactant storage, handling, weighing, and synthesis procedures, resulting in a PO4 deficiency in the final product. In Step 2, a compositional correction based on elemental analysis can be performed to compensate for any PO4 deviations that occurred in Step 1. For this reason, if two vessels are used, graphite can be used in step 1 and nickel in step 2.

[0035] Similarly, if the source is a concentrate of a natural mineral such as magnetite (a mixture of Fe2O3 and FeO), Fe +3 / Fe +2 The ratio may change and should be analyzed frequently. Similarly, metallic iron or manganese may also contain Fe +3 or Mn +3-4 It can be used as a precursor and reducing source, as long as the proportions can be controlled to form the proper stoichiometry of LiMPO4 in conjunction with reactants. Mineral concentrates often contain several percent residual moisture as a result of their manufacture. This moisture content can vary over time, between batches, or even within a batch, and must usually be taken into account when adjusting the feed ratios, or in extreme cases, the mineral concentrate must be thoroughly dried to remove the moisture before use.

[0036] In the present invention, these difficulties are addressed by utilizing a continuous or semi-continuous process using a molten pool as the reaction medium for the reactants, as described in WO 2013 / 177671 A1, but operated differently as a reversible two-stage melt synthesis process characterized by a first step in which the required composition-variable reactants are first introduced into a pool of known mass or volume and stirred at a predetermined temperature and atmosphere to react and achieve a first approximate compositional equilibrium. At this point, the molten pool is maintained in a liquid state at least long enough to allow for melt sampling and analysis to determine the exact Li, M, and PO4 composition. In a second step, the composition of the pool is adjusted to the required chemical composition by adding trace amounts of additional chemically defined reactants based on the analytical data and the known pool mass or volume to be corrected. The additional reactants are added to the vigorously stirred pool under temperature and atmospheric conditions to achieve a new equilibrium with the desired chemical composition and stoichiometry before proceeding to the casting and solidification steps.

[0037] This two-step metal synthesis process can be repeated as needed, followed by additional steps of grinding and particle coating with a conductive phase to form the electrochemically active cathode material. The speed of the chemical reaction, driven by liquid convection, temperature, and agitation in the molten pool, allows for reversible in-situ composition adjustment by taking aliquot samples from the product and using rapid chemical and physicochemical analysis techniques. This is a significant improvement over current solid-state or precipitation-based production processes using other, less flexible phosphate or oxide cathodes.

[0038] This in-situ melt feedback in two-stage melt synthesis allows for the use of chemical sources with a wider range of compositions without the costs associated with complex operating procedures for fine-tuning chemical composition and ratios and controlling reactant stoichiometry. Operating a large, continuous or semi-continuous molten reaction medium pool using a two-stage melt synthesis procedure is a simple and economical process for modifying and controlling the melt composition prior to casting and solidification, improving yield, process economics, product quality, and eliminating the risk of off-spec batches. Depending on the experimental setup and the required compositional accuracy, the modification step 2 can be repeated to further optimize final melt pool composition control.

[0039] Furthermore, as LiMPO4-based lithium batteries have been widely adopted in recent years for many electric vehicles and energy storage applications, not only have the initial cathode and reactant costs become significant factors (approximately 20% of battery material costs), but cathode recycling has become an environmental and cost issue. The present invention not only improves the economics of initial cathode production, but also aids in the recycling of used cathodes and off-spec carbon-coated C-LiFePO4 cathode materials generated in other processes. Currently, chemically converting C-LiFePO4 to isolate new lithium, metal, or PO4 reactant sources is challenging. Recycling C-LiFePO4 from used batteries in random discharge conditions or C-LiFePO4 from off-spec production is possible using the process of the present invention by directly introducing them as reactants of various compositions into the melting process without the need for extensive chemical element separation or prior characterization. Alternatively, many other elements partially separated from the recycling of used LiFePO4 cathodes, such as FePO4, Li3PO4, Li3PO4-Li2SO4 mixtures, or Li-FeO of various compositions. x , as well as Mn-containing compounds, can be used in the present invention as reactants in Step 1 of the present invention, and the composition can be modified in Step 2 to produce well-defined LiMPOs, including LiFePO, LiFeMnPO, and LiMnPO.

[0040] The present invention is based on a melt-stirred reaction pool process for producing high-quality lithium metal phosphate cathode materials of the general composition LiMPO4 (where M is at least one of the following transition metals: Fe and Mn). The first synthesis step involves using composition-variable reactants maintained at elevated temperatures, preferably in the molten state, to arrive at an approximate melt composition, while sampling and physicochemical analysis are conducted. The second step involves using small amounts of chemically defined reactants to fix and equilibrate the final desired composition of the melt based on the results of the physicochemical analysis. Once the desired melt composition is achieved, the melt is cast, solidified, and converted to an electrochemically active cathode material by known pulverization and carbon coating techniques.

[0041] The term "general composition" in the context of the melting process means that the resulting LiMPO4 composition after solidification may contain a few percent, preferably less than 5 mol%, of substitution elements for M elements (e.g., Ca, Mg, Al, Si, etc.) and P elements (e.g., S, B, Si, etc.), and that secondary crystalline or amorphous phases formed during the solidification process are less than 5 mol%. Melt synthesis is particularly advantageous for additions and substitutions to the olivine structure after solidification, and the LiMPO4 composition encompasses such changes as long as the electrochemical activity of the cathode material is derived from the olivine structure and is equal to or greater than the theoretical capacity of 170 mAh / g, preferably 145 mAh / g. For example, crystalline or amorphous phases such as LiPO3, Li3PO4, and Li4P2O7 are frequently induced by adjusting the composition of the melting bath. In the present invention, the preferred final stoichiometry is often stoichiometric LiFePO4 or LiMPO4 with a 3 mol% excess of LiPO3. In such cases, any deficiencies or excesses of Li, Fe, or P after step 1 of the synthesis are corrected by adding the missing elements in step 2 to reach the desired stoichiometry, along with adding a 0.1-5% molar excess of LiPO3.

[0042] The melting process of the present invention is essentially a two-stage continuous or semi-continuous process using a molten pool as the reaction medium. In the first step, reactants are introduced into the molten pool, stirred, and reacted at temperatures preferably between about 800°C and about 1300°C, and maintained under the necessary inert or reducing atmosphere to reach compositional equilibrium and a first approximate LiMPO4 composition. Such a molten pool is then maintained in the molten state for preferably less than 6 hours, more preferably less than 2 hours, and even more preferably less than 1 hour. This time is preferably sufficient to obtain an accurate compositional analysis by taking an aliquot, typically less than 50 g, rapidly solidifying it, cutting / crushing it, and analyzing it with various rapid techniques to determine the stoichiometry of each element and, optionally, the crystal structure, or to confirm the +2 oxidation state of transition metals. In the second synthesis step, accurate Li, M, and P elemental analysis and the mass or volume of the reactive pool from the first step are used to modify the pool melt composition by adding the required amounts of missing elements and stirring the melt to equilibrium at a temperature and atmosphere composition that can be the same as or different from that of Step 1, resulting in the desired final LiMPO4 melt composition, which is then cast, solidified, and ground into a powder. The reactants used to adjust the composition in Step 2 can be the same as those in Step 1 or, optionally, can have well-defined compositions, since only trace amounts are required in this step and rapid reactions are required. It is also within the scope of the present invention that the composition modification between Steps 1 and 2 can accommodate the separation of one or more undesired elements, such as copper, from the melt, typically by liquid-liquid or liquid-solid phase separation. However, a compositional analysis step is used to verify the validity of the modification. Such separation can be applied to other metallic elements that are thermodynamically stable under the reducing conditions of the process, for example, contained Ni or Cr can be separated as second phases of different density induced by their solubility in a second liquid metal phase at the melting temperature, as shown in the examples (like Ag, Sn, Pb as shown in the examples).Other insoluble solid phases are also found when recycling spent lithium battery components and can be phase separated by melt filtration or decantation as controlled by the two-stage and melt analysis of the present invention.

[0043] Natural convection within the reactive melt pool is advantageous for rapidly combining elements, but mechanical and / or gas-assisted stirring of the pool is advantageous, given the densities and viscosities of different reactants and the fact that this process favors the use of coarse reactants such as metallic iron particles and iron ore concentrates. While gas stirring can be used, mechanical stirrers, such as nickel or nickel-chromium, are also suitable for their high melt stability. Depending on the desired melt composition, various gas mixtures can be used during melting and casting. However, inert or buffer gas compositions based on N2, H2 / H2O, or H2 / CO2 are preferred over natural gas because these mixtures are more favorable for a green economy. The term buffer gas composition refers to a mixture of at least two gases, one oxidizing and the other reducing, such as H2 / H2O, CO / CO2, or H2 / CO2, which can fix the oxygen partial pressure (pO2) under thermodynamic equilibrium (as in the Ellingham curve, currently used in metallurgy).

[0044] The molten reaction pool can be the same for Step 1 and Step 2, but a second injector or liquid interconnect pool of known mass or volume can be advantageously used if temperatures and gas compositions are selected to achieve rapid reaction in Step 1 and a final desired compositional equilibrium in Step 2. Graphite is one preferred containment material due to its inertness to the chemical reactants and may currently be used in Step 1. Nickel, chromium, or their alloys, or other high-melting, melt-stable metals can also be used for containment, especially if a second vessel material is used in Step 2.

[0045] The following examples are used to illustrate the procedure of the present invention, which can be further optimized with respect to the nature, heating means and dimensions of the crucible, and to confirm the reversibility and feasibility of the two-stage procedure, the speed of the sampling and analysis technique, and the possibility of in situ correction of the melt composition based on feedback from aliquot analysis.

[0046] Furthermore, the present invention allows for the use of multiple melt containers at each step by pouring some or all of the melt from one container (the melting container) into another (the holding container). Large melt pools are recommended to minimize repetitive elemental analysis and costs. Rapid analytical techniques include electron diffraction spectroscopy (EDS), glow discharge mass spectrometry (GD-MS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), laser-induced breakdown spectroscopy (LIBS), X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), inductively coupled plasma mass spectrometry (ICP-MS), and microwave plasma atomic emission spectrometry (MP-AES). To reduce energy costs and improve productivity, techniques that allow direct analysis of solid / powder samples without the need for decomposition or melting are recommended.

[0047] Complementary, the possibility of determining melt composition through the activity of major components using online gas analyzers such as FTIR and MS can further reduce the reliance on aliquot extraction and preparation, while relating the results from gas analysis to the liquid composition through either a thermodynamic model or a well-tuned interaction matrix. In this context, aliquot extraction also includes the activity of such indirect components. At a minimum, online gas monitoring should allow for the melt to equilibrate and adequately assess the oxidation state of the melt as a result of the CO / CO2 and / or H2 / H2O ratios (i.e., pO2). For safety, cost, and toxicity reasons, one preferred gas composition to use is a mixture of N2, CO2, and H2, which can be used in both steps. Alternatively, steam (H2O) can be used instead of CO2, as long as the flow rate can be controlled with sufficient precision and condensation can be avoided.

[0048] The economic advantages of this invention include a broad range of Li-, M-, P-, and O-containing reactants without the need for strict composition specification or careful manipulation, given the option of in situ composition modification in the melt pool before casting, as well as increased productivity in continuous or semi-continuous processes where rapid equilibration between reactants and, if necessary, gas can be achieved by stirring the liquid pool before and after melt sampling and reactant addition. This invention not only enables well-defined LiMPO4 compositions to be achieved from variable reactant compositions, but also reduces the risk of producing off-spec batches. Furthermore, this two-step melt synthesis also facilitates the recovery of off-spec C-LiMPO4 products from other synthesis processes, ultimately enabling the recycling of C-LiMPO4 recovered from spent batteries by directly using them as reactants in the two-step synthesis. In such cases, the carbon coating or conductive carbon powder can be removed by oxidation or mechanical separation from the melt. It can also be removed in a preliminary step prior to the process of this invention.

[0049] Examples from the glass and steel manufacturing industries provide a variety of containment crucible designs and sizes, heating means (fossil combustion heating or environmentally friendly electric induction heating, radiant heating, resistance heating), and continuous or semi-continuous casting procedures. Preferred materials for containment, either directly or via autocrucible, can be graphite, oxide, nitride, carbide, boride ceramics, and high-melting and melt-stable metals such as nickel, chromium, and their alloys.

[0050] Due to the cost of maintaining a large pool of molten LiMPO4 before final reactant addition and melt homogenization to the final cast composition, the speed and accuracy of chemical and physical analyses are critical factors in optimizing the process of this invention. Compositional analysis of the melt is preferably performed by sampling the liquid melt, followed by rapid casting / quenching (e.g., liquid nitrogen, water, dry ice), and, if necessary, cutting / polishing / crushing / grinding into a sample ingot or fine powder, or, in extreme cases, melting or fusion for rapid elemental analysis. While several analytical techniques are possible, preferred are those that allow for measurement of solid samples that can be prepared within 5–10 minutes of collection in the molten state. Such techniques include glow discharge mass spectrometry (GD-MS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), laser-induced breakdown spectroscopy (LIBS), and X-ray fluorescence spectrometry (XRF), all of which provide quantitative elemental analysis within minutes of measurement time. On the other hand, X-ray diffraction (XRD) can perform physicochemical analysis to determine structure within 1–2 hours without requiring high elemental quantitative accuracy. Furthermore, XRF is not sensitive to lithium, so it does not provide information regarding lithium quantification. Alternatively, other techniques requiring more sample preparation time, such as dissolution, which can take several hours to measure, depending on the retention volume and time, can be considered. Such techniques include absorption atomic spectroscopy (AAS), inductively coupled plasma optical emission spectroscopy (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), and microwave plasma atomic emission spectroscopy (MP-AES), because they can provide sufficient accuracy and feedback on the composition of Li, M, P, or PO4 elements in a short time, preferably less than 2 hours. Fe +2 / Fe +3 Titration can be used for more complete feedback on melt composition. LECO analysis complements other analytical techniques and can measure accurate C content within 10 minutes when using C-LiMPO4 as a reactant, ensuring carbon is removed to the required extent before casting.

[0051] After compositional modification and final homogenization of the melt at temperatures between about 800 °C and about 1300 °C, depending on the composition of the melt, the liquid phase is partially or totally cast to obtain solid and crystalline LiMPO4 with an olivine structure. In some cases, depending on the composition of the reactive melt, phase separation or filtration of the melt can be used as part of step 1 or at the end of step 2 before casting.

[0052] Two-stage continuous or semi-continuous synthesis operations can be performed in the same vessel or using multiple vessels. The first operation is limited to the synthesis of the crude composition, while the last operation is a liquid interconnection or injection, the volume of which is known to achieve the precise final composition, and is used to cast the LiMPO4. In such cases, the connection between the vessels is achieved by connecting or injecting the melt. Large melt pools are preferred to increase productivity, reduce specific energy losses and costs during heat holding, and reduce the number of required analyses. For mass production and high precision, the analysis and step 2 may be repeated.

[0053] The subsequent casting, grinding, and carbon coating steps to obtain electrochemically active LiMPO or C-LiMPO cathodes are described in prior patents (WO 2005 / 062404 A1, WO 2013 / 177671 A1, WO 2015 / 179972 A1) and include melt atomization, ingot casting, grinding (including crushing, grinding, jet milling, and wet milling) down to micron, submicron, or nanoscale primary particles depending on the exact composition of the LiMPO and the requirements at the battery level.

[0054] A further advantage of the present invention is that by fine-tuning the melt composition in Step 2, not only the fluctuation of the reactant composition but also the evaporation, scattering, and deposition of transient Fe on the vessel wall during the synthesis in Step 1 can be minimized. x P and Fe xThis allows for compensation of reactant losses due to the formation of LiPO3, container equilibrium effects, and reaction rate retardation due to sintering. Furthermore, in addition to correcting the melt composition to stoichiometry, it is also possible to intentionally deviate from the stoichiometry, for example, by creating a slight excess of LiPO3. This results in the presence of intercrystalline LiPO3-containing phases that act as conductive phases when the olivine crystalline phase forms during solidification. Similar to conventional pyrolytic carbon coatings, these phases contribute to improving the electrochemical behavior of the cathode material. In such cases, rapid solidification of the melt by high-speed casting or spray quenching is often preferred to avoid the growth of large (several micron) olivine crystals and the formation of intercrystalline non-olivine phases. This is because grinding to submicron sizes results in the formation of individual, non-redox-active particles such as LiPO3, Li4P2O7, and Li3PO4. While these phases are useful as conductive phases for lithium ion exchange on the olivine particle surfaces, they also contribute to the improvement of the electrochemical behavior of the cathode material. +2 / M +3 This is because it does not contribute to redox energy storage itself and results in a deadweight penalty. In a useful variation of the present invention, the initial molten pool in step 1 may be a mixture of only a low melting reactant or only a reactant such as LiPO3 (melting point approximately 660°C). To this, auxiliary elements may be added to achieve the desired molten composition (in this case FeO equivalent (e.g., Fe2O3 + Fe 0 )) In this method, an excess of LiPO3 relative to the stoichiometry of LiFePO4 is usually preferred, and this excess amount is fixed in step 2 based on chemical element analysis so that crystalline olivine and LiPO3-containing phases coexist after casting and solidification.

[0055] A step of agglomerating the elementary particles into secondary agglomerates is also part of the present invention, e.g. conductive carbon coated C-LiMPO4, in particular LiFePO4 and LiFePO4, preferably obtained by spray drying or flash drying before pyrolysis. 1-x Mn x Produce PO4 (x is 0-1). [Example]

[0056] The following example is presented to illustrate the operating mode of the two-stage melting process of the present invention using standard laboratory equipment. For optimal economic and technical feasibility, it can be scaled up to larger industrial processes at kilogram and ton levels. The times required for melting in steps 1 and 2, as well as the time required for analysis in the analytical step, have not been optimized for this laboratory demonstration. Those skilled in the art will appreciate that these times can be reduced, for example, by using mechanical stirring instead of gas stirring. Similarly, the graphite crucible can be advantageously replaced with a high-melting-point, melt-compatible metal, such as Ni, Cr, and their alloys.

[0057] Example 1 In this example, a known amount of pure Aldrich Fe2O3 (Fe +3 ) micron-sized powder, micron-sized iron powder Fe 0 (Rio Tinto QMP Atomet 1001HP, (45μm~250μm)) and all iron ions were removed by Fe +2 The iron precursors are mixed in the ratio required to stabilize the oxidation state. This mixed iron precursor is then added to a 100g LiFePO4 molten pool along with solid PO powder (containing 5 mol% water) and LiCO powder in the required proportions. This produces an additional 100g of stoichiometric LiFePO4, assuming the added PO is pure (water-free). The melt is held at 1150°C by resistive heating in a graphite crucible under a 5% H / CO atmosphere containing N, to complete the reaction in step 1. During and after addition of the reactants to the melt, the liquid melt is mechanically stirred to complete the reaction and allow it to equilibrate for 30 minutes. At this point, a liquid aliquot of approximately 3mL is extracted and poured into a container filled with liquid nitrogen, crushed, and dissolved for 4 hours. Standard ICP-MS analysis is then used to analyze Li, Fe, and P to determine the ratios of each element. As expected, chemical analysis confirmed a deficiency of P relative to Li and Fe. During the analysis, the melt was kept above 1000°C (>1000°C) due to the reducing atmosphere conditions, and no excessive corrosion of the crucible occurred.

[0058] Based on the gravimetric measurement of the initial LiFePO4 pool and the weights of the three reactants introduced, and assuming pure P2O5 (P2O5 + H2O), the P-deficient LiFePO4 melt composition is corrected in step 2 by adding sufficient LiPO3 to the melt to achieve a 1:1 P to Fe ratio with a slight excess of Li.

[0059] To complete the synthesis of Step 2, the melt was mechanically stirred for an additional 30 minutes at the same temperature and atmosphere, after which a portion of the melt was cast, solidified, and ground to less than 75 μm for XRD and elemental analysis. Chemical analysis of the resulting powder confirmed a 1:1 Fe / P ratio, and XRD measurements, shown in Figure 1, confirmed a pure olivine structure with traces of the Li3PO4 phase.

[0060] This example is constructed from a laboratory setup solely to demonstrate the reversibility of the phosphorus-deficient approximate "LiFePO4" melt composition observed after step 1 through a second synthesis step guided by laboratory melt analysis, and thereby demonstrate the feasibility of using a P2O5 reactant of variable composition and still obtain well-defined LiFePO4 olivine.

[0061] In large-scale production, optionally, the gravimetric measurement of the melt pool can be replaced with a melt volumetric measurement in the same pool container, or after step 1, some or all of the melt can be poured into a second pool container of known volume to complete step 2.

[0062] Example 2 In this example, the same experimental procedure as used in Example 1 is applied. 100 g of LiFePO4 forms a molten pool, to which another 100 g of LiFePO4 is synthesized by introducing a compositionally variable mixture of lithium precursors made from a mixture of 95 mol% Li3PO4 and 5 mol% Li2SO4. For example, a mixture that can be obtained from spodumene mineral treatment with H2SO4 and orthophosphate precipitation. Pure and dry P2O5, Fe2O3, and Fe 0 Add this additional 100 g to complete the synthesis.

[0063] The reactant proportions of Li, Fe, and PO4 to obtain the stoichiometry of LiFePO4 are determined by considering the Li2SO4-contaminated Li3PO4 as pure Li3PO4, so that the molten composition after step 1 is found to be deficient in lithium and PO4.

[0064] Based on the ICP-MS chemical analysis after step 1, the required amounts of LiPO and PO are added to the melt stirred for 30 minutes under N, CO / H atmosphere in Example 1. After casting, solidification, and grinding, a pure LiFePO olivine structure is confirmed by XRD, as shown in Figure 2.

[0065] Example 3 In this example, a coarse (approximately 540 μm) iron oxide powder mixture with a composition close to Fe2O3, available in the steel industry and known as ARO (Acid Regenerated Oxide from Arcelor-Mittal Dofasco), was used, to which an excess of 5 wt% Fe2O3 was added to simulate an iron reactant of variable composition. 0 The powder and LiPO are also simultaneously added to a pool of molten LiFePO stirred with a strong CO / H / N gas mixture at a temperature of 1150°C to promote compositional equilibration. After 30 minutes in step 1, sampling and analysis are performed as described in Example 1 to confirm the excess of iron in the melt.

[0066] In the second synthesis step, additional LiPO3 is used to modify the composition of the iron-rich melt, the temperature is reduced to 1100°C, CO2 / H2 / N2 gas (5%:5%:90%) is injected and the melt is vigorously stirred for 1 hour, and a second analysis confirms the "LiFePO4" composition. In this case, stirring the melt is important because excess iron is released into the Fe x P and Fe x C. After equilibrium is achieved, the melt is cast, solidified, and crushed. XRD analysis confirms a pure LiFePO4 olivine structure similar to that shown in Figure 2 of Example 2.

[0067] Example 4 In this example, 174 g of off-spec C-LiFePO containing 10 wt. % C (rather than the usual 1.5% C pyrolysis composition optimized for electrochemistry) was first oxidized in air at 550 °C to burn off any carbon coating and form a homogeneous mixture of FeO and LiFe(PO). This mixture was then treated as a reactant in the process steps of the present invention by gradually introducing it into a pool of 158 g of molten stoichiometric LiFePO (1:1:1) composition held at 1150 °C for 1 hour while stirring the melt under a reducing atmosphere of CO / H / N (5%:5%:90%), as in Example 3. At that point, two aliquots were withdrawn and analyzed: one for LECO analysis to confirm C removal, and the other for Fe, Li, and P content by standard ICP analysis to confirm the correct LiFePO melt composition.

[0068] In the second step, the overall melt composition is modified by adding LiPO3 powder not only to recycle off-spec material but also to change the final melt composition to LiFePO4 + 3 mol% LiPO3 before casting after stirring at 1150 °C for 30 min under a CO2 / H2 / N2 (5%:5%:90%) atmosphere. Structural XRD and microscopic analysis of the resulting ingot confirmed the olivine structure of LiFePO4, and Li was analyzed in the final product. 1.03 Fe1P 1.03 O 4.09Among the Li- and P-rich intercrystalline phases observed in the overall composition, some Li3PO4 and Li4P2O7 phases are probably present (see Fig. 3).

[0069] Example 5 In this example, another 174 g of the off-spec C-LiFePO4 material from Example 4 is first oxidized as described above and slowly introduced into a pool of 158 g of molten stoichiometric LiFePO4 (1:1:1) composition and held with stirring at 1150°C for 30 minutes under a reducing atmosphere of CO2 / H2 / N2 (5%:5%:90%). At that point, two aliquots are taken and analyzed: one for LECO analysis to confirm the removal of C, and one for Fe, Li, and P elemental analysis based on ICP standard analysis to confirm the correct composition of the LiFePO4 melt.

[0070] In the second step, 230g of MnCO3 and 172g of LiPO3 powder were introduced to change the overall melt composition to a new, different product, replacing the off-spec C-LiFePO4 with the new LiFe 0.5 Mn 0.5 This is confirmed by the XRD analysis and cell parameters in Figure 4, which show that the lattice volume after step 2 is 296.83 Å. 3 The lattice volume of the material after step 1 is 291.09 Å. 3 It was.

[0071] Example 6 Describing another variation of the present invention, the molten pool in Step 1 is first formed with a known amount of low melting point LiPO3 held at 1050°C. As part of Step 1, Rio Tinto refined iron ore concentrate (of known but variable composition) is melted with Fe3O4-Fe2O3 and Fe 0It is mixed with Atomet powder. The latter is added to approximate the overall FeO composition. This solid mixture is gradually introduced into the melt, where LiPO3 reacts with FeO to form LiFePO4. To account for the imprecise Fe content, the equivalent of 210 g of FeO is added to 300 g of molten LiPO3, which is stirred and kept under a reducing atmosphere of CO2 / H2 / N2 (5%:5%:90%). Such an excess is used to dissolve solid Fe. x This is preferred as it avoids P formation.

[0072] Elemental analysis performed at the end of step 1 confirmed an excess of Li and P, followed by a well-defined Fe2O3+Fe 0 After casting and solidification, a pure LiFePO4 olivine structure was confirmed by XRD, which resembles Figure 2 in Example 2, demonstrating the flexibility and simplicity of the two-step process of the present invention in terms of reactant selection and process operation.

[0073] Example 7 In this larger-scale example, approximately 5 kg of off-spec C-LFP powder, which XRD revealed contained excess Li3PO4 but whose composition was otherwise unknown, was first oxidized in air at 550 °C to burn off any excess carbon coating and form an intimate Fe2O3 + Li3Fe2(PO4)3 mixture. This mixture was then treated as a reactant in the process steps of the present invention, gradually introduced into an induction melting furnace, heated to a molten state at temperatures between 1050 °C and 1100 °C, and held for 30 minutes to ensure complete melting. A 25 mL aliquot of the melt was taken and rapidly cooled in a liquid nitrogen-cooled stainless steel mold under an argon atmosphere. After 5 minutes, the outer surface of the sample disk had cooled sufficiently (below 100 °C) to allow it to be handled in air without risk of oxidation.

[0074] Without further sample preparation, a LIBS surface mapping analysis was performed on the flat underside of the sample disk. The bulk composition was determined to confirm the presence of 12.8% (mol / mol) excess Li and 4.3% (mol / mol) excess P relative to Fe. The analysis took less than 10 minutes to perform.

[0075] The melt temperature was maintained near 1050 °C during sample collection / cooling and LIBS analysis. After the composition was obtained from LIBS, corrections were made to the final composition to achieve a 5% excess Li and 3% excess P by adding 0.142 kg of P2O5 (microcrystalline, Clariant) and 0.183 kg of Fe2O3 (fine particle ARO, RTC rehydrochloride). These amounts were weighed and co-charged into the hot melt. The hot melt was held for an additional 30 minutes with H2 / CO2 (1:4) bubbling before being cast and allowed to cool overnight.

[0076] The composition of the final ingot and sample disk fragments was later analyzed by XRD and MP-AES. XRD analysis, shown in Figure 5, qualitatively confirmed the reduction in Li3PO4 between the initial sample and the final ingot, with each measurement taking approximately 1 hour. MP-AES results were within ±0.3% of the LIBS analysis results, and the final ingot was determined to have a 6% excess of Li and a 3% excess of P. In this non-optimized analytical test, the time required for sample preparation (milling), disassembly, and analysis was approximately 4 hours.

[0077] Example 8 In this example, LiH2PO4 and MnCO3 were added to a "dirty" graphite crucible previously used for LiFePO4 synthesis in a ratio that would produce 3.75 kg of the stoichiometric amount of LiMnPO4. An unknown amount (approximately 100 g) of LiFePO4 remained on the surface of the crucible. Step 1 and the intermediate sampling steps were carried out as in Example 7.

[0078] LIBS surface mapping analysis was performed on the flat underside of the sample disk to confirm the bulk composition, which was determined to be 0.8% (mol / mol) Fe relative to Mn.

[0079] Taking into account the excess Li and P from Example 7, 1.284 kg of off-spec C-LFP was added to the melt to produce LiFe with 3% (mol / mol) excess Li and 2% (mol / mol) excess P and an x ​​value of 0.75. 1-x M x Once the off-spec LFP was added, the hot melt was held for an additional 30 minutes with argon blowing before casting and then cooled overnight under argon flow.

[0080] The composition of the final ingot and sample disk fragments was later analyzed by XRD and MP-AES, and the composition was confirmed. The XRD patterns in Figures 6A and 6B show a pure microstructure after steps 1 and 2, with a melt-composition-corrected lattice volume of 302.54 Å. 3 to 299.70Å 3 The change in the lattice parameter after correction decreases from LiMnPO4 to LiFe 0.25 Mn 0.75 Transition to PO4 has been confirmed.

[0081] Example 9 This example aims to illustrate direct elemental analysis of the melt in the context of refining and recycling black mass materials. In Example 9a, 50 g of LiFePO4 powder and 1 g of copper (Cu) from a previous ingot are added to the powder. The mixture is placed in a graphite crucible, covered with a grafoil lid, and held at 1100 °C for 1 hour. The liquid melt is then slowly cooled in the crucible under a N2 atmosphere. Interestingly, as shown in Figure 7a, large concentrated Cu droplets are visible at the bottom of the ingot. Even more interesting is that the resulting ingot contains only 1060 ppm Cu, as determined by MP-AES, when 4.4% mol Cu / mol LFP was added to the starting mixture. This is due to the fact that Cu is thermodynamically stable in the metallic state under reducing conditions in the melt at high temperatures, and the density of the molten LFP, approximately 2.75 g / cm. 3 Compared to copper, 8.96 g / cm 3This can be explained by the fact that the copper chips are highly dense (~1000µm). Similar results are obtained with copper chips from a copper current collector. Although not optimized, this example demonstrates that liquid-liquid physical separation of Cu from a melt is possible.

[0082] Example 9b is the same as Example 9a, except that a metal bath of Ag is placed below the LFP-Cu starting mixture. 50 g of LiFePO4 powder and 1 g of copper oxide from the previous ingot are added to the powder. 150 g of Ag is placed at the bottom of the crucible as an impurity trap. The mixture is poured into a graphite crucible, covered with a grafoil lid, and held at 1100 °C for 1 hour. The liquid melt is then slowly cooled in the crucible under a N2 atmosphere. Once cooled, the LFP ingot can be easily separated from the metal ingot. In contrast to Example 9b, no Cu droplets are found at the bottom of the ingot, as shown in Figure 7b. Interestingly, with 4.4% mol Cu / mol LFP added to the starting mixture, the resulting ingot contains only 400 ppm Cu as measured by MP-AES, indicating that most of the copper is trapped within the metal ingot. In this case, Cu contaminants are extracted from the LFP melt by alloying with a metallic Ag layer. While not optimized, this example demonstrates the ability to purify Cu or other metals that are stable under smelting and reduction conditions. This is important not only for mineral refining but also for recycling phosphoric acid cathodes from black mass.

[0083] As will be appreciated by those skilled in the art, phase separation of Cu metal and molten LFP can be easily accomplished in liquid Step 1. In-situ melt analysis of copper by LIBS or ICP will aid in determining the time required to reach the desired residual Cu concentration in Step 2 of the present invention.

[0084] Throughout sample collection / cooling and LIBS analysis, the melt temperature can be maintained near 1050 °C until the Cu concentration progresses as a result of precipitation and / or diffusion into the metal layer, causing the melt composition to fall below a predefined limit.

[0085] Those skilled in the art will appreciate that other variations and combinations may be made to the various embodiments of the invention described hereinabove.

[0086] While the present invention has been described in connection with particular embodiments thereof, such embodiments are capable of further modification, and this application is generally intended to cover any variation, use, or alteration of the invention in accordance with the principles of the invention, and will be understood to include departures from the present disclosure that come within known or customary practice within the art to which this invention pertains and that may apply to the essential features set forth above and that fall within the scope of the following appended claims. Features that are described in the context of separate aspects and embodiments may be used together and / or interchangeable. Similarly, features that are described in the context of a single embodiment may also be provided separately or in any suitable subcombination.

[0087] These descriptions cite numerous documents, the contents of which are incorporated herein by reference in their entirety.

[0088] The scope of the claims should not be limited by the preferred embodiments set forth hereinabove, but should be accorded the broadest interpretation consistent with the entire description.

Claims

1. Lithium metal phosphate (LiMPO) with a specified composition ４ 2.) A two-stage melting process for producing a cathode material, comprising a first melting step and a second melting step, and an intermediate analysis step between the two melting steps; the first melting step includes mixing reactive precursors to form a first molten pool having a first molten pool composition; the second melting step includes adjusting the composition of the first molten pool based on results obtained from the intermediate analysis step to obtain a second molten pool having the specified composition; the reactive precursor comprises a material selected from the group consisting of Li-, M-, P-containing materials, spent positive electrode materials from spent batteries, off-spec positive electrode materials, and combinations thereof; M is at least one transition metal; Optionally, a two-stage melting process, wherein the second melting step and the intermediate analysis step are repeated multiple times.

2. the first melt pool composition determined by the intermediate analysis step is found to be P-deficiency and / or Li-deficiency and / or M-excess and / or the presence of undesired elements, and the second melting step comprises adding a P-containing material to the first melt pool, and / or adding a Li-containing material to the first melt pool, and / or adding an M-containing material to the first melt pool, and / or injecting a gas flow into the first melt pool, and / or extracting the undesired elements; Preferably, the undesired elements are metal elements that are thermodynamically stable at the melting temperature, more preferably, the undesired elements include Cu, Ni, and / or Cr, and even more preferably, the undesired elements include Cu; Preferably, the gas stream is CO ２ , H ２ , N ２ 10. The process of claim 1, comprising:

3. the reaction precursor comprises spent positive electrode material from spent batteries, off-spec positive electrode material, or a combination thereof; the first molten pool composition determined by the intermediate analysis step includes undesirable elements; 3. The process of claim 1 or 2, wherein the second melting step comprises extracting the undesired elements from the second molten pool, preferably by liquid-liquid or liquid-solid phase separation.

4. 4. The process of claim 3, further comprising a preliminary step of removing any carbonaceous material by combusting the material before carrying out the first melting step.

5. 5. The process of claim 3 or 4, wherein the first molten pool and the second molten pool are each independently subjected to oxidation and / or mechanical separation to remove any carbon material.

6. the reactive precursor comprises a material containing a first metal M1, i.e., an M1-containing material, and the second melting step comprises adding a material containing a second metal M2, i.e., an M2-containing material, to the first molten pool; The process according to any one of claims 1 to 5, wherein preferably M1 is Fe and M2 is Mn.

7. the first melting step and the second melting step are carried out at a first temperature and a second temperature, respectively, under an inert and / or reducing atmosphere, and the first molten pool is maintained at the first temperature and in the inert and / or reducing atmosphere during the intermediate analysis step; Preferably, the first temperature and the second temperature are each independently between about 800°C and about 1300°C, more preferably greater than 1000°C; Preferably, the inert atmosphere and / or the reducing atmosphere is Ar, CO ２ , H ２ , N ２ The process of any one of claims 1 to 6, comprising the use of:

8. The process of any one of claims 1 to 7, further comprising a post-synthetic step.

9. a first post-synthesis step including subjecting the second molten pool to a casting, solidification, and grinding process to obtain a powdered, particle-sized reduced material; 9. The process of claim 8, wherein the particle size is preferably in the micron, submicron, nano, and combinations thereof range.

10. A second post-synthesis step involves subjecting the particle size reduced material to a coating process with an electrochemically active material to produce electrochemically active LiMPO. ４ obtaining a positive electrode material; 10. The process of claim 9, wherein the electrochemically active material preferably comprises carbon.

11. 11. The process of any one of claims 1 to 10, wherein the first melting step and the second melting step are carried out in a first vessel and a second vessel, respectively, and the first vessel and the second vessel are different or the same.

12. 12. The process of any one of claims 1 to 11, wherein the first and second melting steps are each independently performed by mechanical and / or gas-assisted stirring of the molten pool.

13. 13. The process of any one of claims 1 to 12, wherein the first melting step and the second melting step each independently comprise phase separation or filtration of the melt.

14. The process of any one of claims 1 to 13, wherein the metal M is Fe or Mn, or both Fe and Mn.

15. The Li-containing material is LiOH, Li ２ CO ３ , Li ２ SO ４ , Li ３ P.O. ４ , LiPO ３ , LiH ２ P.O. ４ 15. The process of any one of claims 1 to 14, wherein the compound is selected from the group consisting of:

16. The M-containing material is an Fe-containing material, ０ , Fe ２ O ３ , FeO, FeSO ４ 16. The process of any one of claims 1 to 15, wherein the ore is selected from the group consisting of concentrated ores such as hematite and magnetite, and combinations thereof.

17. The M-containing material is a Mn-containing material, ０ , MnCO ３ , MnO ２ , Mn ２ O ３ , Mn ３ O ４ , MnO, MnSO ４ 17. The process of any one of claims 1 to 16, wherein the manganese ore is selected from the group consisting of: pyrolusite, rhodochrosite, and concentrated ores such as hausmannite, manganese-rich alloys such as ferromanganite (Mn+Fe), and combinations thereof.

18. The P-containing material contains P ２ O ５ , Li ３ P.O. ４ , LiPO ３ , LiH ２ P.O. ４ , (NH ４ ) ２ HPO ４ , (NH ４ ) H ２ P.O. ４ 18. The process of any one of claims 1 to 17, wherein the compound is selected from the group consisting of:

19. The used positive electrode material or the off-spec positive electrode material is a carbon-coated LiMPO ４ , FePO ４ , Li ３ P.O. ４ , Li ３ P.O. ４ -Li ２ SO ４ Mixtures, variable composition Li—FeO ｘ and a Mn-containing compound.

20. 20. The process of any one of claims 1 to 19, wherein the intermediate analysis step comprises using a rapid analytical technique selected from the group consisting of electron diffraction spectroscopy (EDS), glow discharge mass spectroscopy (GD-MS), laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS), laser induced breakdown spectroscopy (LIBS), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), inductively coupled plasma mass spectroscopy (ICP-MS), microwave plasma atomic emission spectroscopy (MP-AES), and combinations thereof.

21. 21. The process of any one of claims 1 to 20, wherein the intermediate analysis step comprises determining the first melt pool composition using an online gas analyzer, preferably the online gas analyzer is FTIR or MS.

22. 22. The process of any one of claims 1 to 21, which is continuous or semi-continuous.

23. The LiMPO ４ The process of any one of claims 1 to 22, wherein the cathode material has an olivine structure.

24. The LiMPO ４ The positive electrode material is electrochemically active, Preferably, the LiMPO ４ The process of any one of claims 1 to 23, wherein the positive electrode material is carbon coated.

25. LiMPO obtained by the process defined in any one of claims 1 to 24 ４ Positive electrode material.

26. LiFePO ４ , LiFe １－ｘ Mn ｘ P.O. ４ , and LiMnPO ４ wherein x varies between 1 and 0. ４ Positive electrode material.

27. 27. A battery wherein the positive electrode comprises a material as defined in claim 25 or 26.

28. A cathode or battery manufacturing plant carrying out a process as defined in any one of claims 1 to 24.

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