A process for producing a cathode material from an iron source

Abstract

A process for producing a iron lithium metal phosphate cathode material from an iron source comprising the steps of: (a) optionally chemically treating the iron source to provide a residue enriched in iron-bearing materials relative to the iron source; (b) converting the iron source to produce iron phosphate cathode active material precursor (pCAM); and (c) converting the iron phosphate pCAM to produce high energy dense lithium metal phosphate battery cathode with a tuned particle size.

Description

A PROCESS FOR PRODUCING A CATHODE MATERIAL FROM AN IRON SOURCE TECHNICAL FIELD

[0001] The present invention relates to a process for producing a cathode material from an iron source such as iron ore. BACKGROUND ART

[0002] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0003] Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirety by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application or patent cited in this text is not repeated in this text is merely for reasons of conciseness.

[0004] Lithium metal phosphate (LiFexM1-xPO4 including lithium iron phosphate, LFP) are commonly used battery cathode materials as they generally provide better electrochemical performance, good temperature stability, better safety, and good cycle life than other battery materials. The better electrochemical performance and improved safety aspects make them suitable for use in electric vehicles, energy storage and a range of other applications. Use of lithium metal phosphate cathodes will continue to increase and will occupy a sizable proportion of lithium iron battery (LIB) cathodes.

[0005] Direct conversion of mined iron ores to lithium metal phosphate battery precursor (pCAM) and cathodes without significant processing is interesting from an economic and environmental point of view. However, iron ore from mines is associated with high levels of gangue impurities (e.g silicon and aluminium containing minerals) and cannot directly be converted into battery cathode materials.

[0006] The physical purification methods, traditionally used in the iron ore industry, cannot improve the ore quality beyond a certain extent and so cannot meet the strict requirements for battery cathodes. As such, iron ores are first converted into iron viareduction with carbon in a blast furnace. This process allows removal of gangue as a slag with an impure iron metal stream then undergoing different conversion stages to form high purity iron precursors for cathode production (e.g. iron oxalate, iron phosphate, synthetic iron oxides etc.). For example, the iron produced in the blast furnace is converted into iron salts using acid digestion. As produced, iron salts are further purified and then converted into iron precursors for lithium metal phosphate battery cathodes.

[0007] Chemical purification is an alternative to traditional physical ore processing methods commonly used in the iron ore industry. Typically, high phosphorus (P) content in ore is problematic in steel making processes as it induces brittleness in steel products. Since physical processing methods are unable to effectively reduce P in ores, most chemical purification methods have been explored for the removal of P in the iron ore. As such, different chemical purification methods using acids and / or alkali have been explored for removing P from the iron ore. Only limited studies have been conducted on chemical purification of iron ore for the removal of Si and Al especially in the context of battery cathodes.

[0008] It is therefore important to develop a low-cost technology capable of effectively remove gangue impurities, in particular the high levels of Si and Al from the iron ores for use as feed materials for battery cathodes.

[0009] Industrial scale processes to produce lithium metal phosphate mainly include high temperature solid phase reaction, carbothermal reduction, hydrothermal synthesis, sol-gel synthesis etc. Amongst them, carbothermal reduction is the most widely used method as the process is simple, easy to control, and can produce lithium metal phosphate in one-step reduction with minimal waste production. Depending on the iron source used, carbothermal reduction process can be divided into the iron phosphate route and the iron oxide route. Since the quality of lithium metal phosphate cathodes manufactured using iron oxide is difficult to control, it results in inferior cathodes as compared to iron phosphate. In addition, high purity iron oxides are typically required for lithium metal phosphate synthesis, which are not readily available and make them as expensive source of iron. Another advantage of iron phosphate is that it contains both the iron and phosphorus source required for the synthesis of lithium metal phosphate which simplifies the synthesis process. Thus, iron phosphate has become the preferredcathode precursor (i.e., pCAM) for the synthesis of lithium metal phosphate cathode materials, particularly lithium iron phosphate (LFP) cathode material.

[0010] Anhydrous Iron phosphate (FePO4) and iron phosphate dihydrate (FePO4.2H2O) are two commonly used iron phosphate pCAM for lithium metal phosphate synthesis. The ratio of iron to phosphorus is an important index for iron phosphate that determines the quality of lithium metal phosphate. High quality and near stoichiometric iron phosphate dihydrate is white or pinkish white in color while the anhydrous iron phosphate is pale yellow in color. Excess phosphorus in iron phosphate dihydrate on the other hand presents as a grey-white or dark grey-white appearance while excess iron presents a dark yellow appearance. Thus, it is important to control the stoichiometry of iron phosphate pCAM to produce high quality lithium metal phosphate. Besides the proportion of iron and phosphorus in iron phosphate, the inclusion of impurities is also an important consideration that determines their quality for producing lithium metal phosphate cathode.

[0011] Commercial iron phosphate is prepared using soluble salts of iron such as iron sulphate together with the phosphorus source such as phosphoric acid or sodium phosphate. Generally, pH of the resulting iron sulphate and phosphate solutions are increased to induce the formation of iron phosphate. However, the pH of conversion reaction is difficult to control, and localised regions of high and low pH are created during mixing. This can lead to the production of impurity phases such as iron hydroxides as well as entrainment of undesirable impurities such as sodium and potassium. This process also generates waste by-products such as sodium sulphate or ammonium sulphate which have started to become a major issue globally and a constraint to meet the increased demand for lithium metal phosphate cathodes. Other methods to prepare iron phosphate are either time consuming, limited to a specific iron or phosphorus source, or are generally not commercially attractive. Thus, an efficient, flexible, and low-cost process with minimal waste generation is desirable to produce iron phosphate pCAM.

[0012] Furthermore, energy density of batteries are important metrics for mobility applications where space and weight limitations exist. With the increased uptake of lithium metal phosphate batteries in electric vehicles and energy storage applications, the desire for high density metal phosphate cathodes with good performance is ever increasing. Energy density of lithium metal phosphate cathode materials is greatlyinfluenced by their quality and physical properties. For example, lithium iron phosphate (LFP) typically has a bulk density of 3.6 g / cc, however, the density of LFP cathodes is generally low due to the requirements of nano-sizing and conductive coating (e.g., carbon coating) for optimal performance. Control over LFP particle size and conductive carbon content determines its use in either high power batteries or high energy batteries. Typically, larger sized LFP with reasonable carbon content is desired for high energy batteries while smaller sized LFP with high carbon content is desired for high power batteries. Besides, the commercial battery electrodes are composed of differently sized cathode particles to improve their packing density. Thus, an ability to precisely control the crystal size of lithium metal phosphate cathodes will enable a greater flexibility to meet the needs of specific applications.

[0013] Sintering temperature and conductive carbon content is generally altered to tune the particle size of metal phosphate cathode. Increasing the temperature increases the particle size while increasing the carbon content decreases the particle size. Control over metal phosphate particle size to achieve high energy density without significant compromise on carbon content is difficult. Similarly, increasing the sintering temperature beyond a certain point introduces undesired impurity phases that negatively impact battery life. In addition, the lithium metal phosphate particles require to be sintered for long time (>10 hr) to achieve desired materials for high density cathodes. The current lithium metal phosphate production process is generally not effective for production of high energy density cathodes and this need remains to be fulfilled.

[0014] The present invention has been developed against the above background. SUMMARY OF INVENTION

[0015] In one aspect, the present invention provides a process for producing a iron lithium metal phosphate cathode material from an iron source comprising the steps of: (a) optionally chemically treating the iron source to provide a residue enriched in iron-bearing materials relative to the iron source; (b) converting the treated iron source to produce iron phosphate cathode active material precursor (pCAM); and(c) converting the iron phosphate pCAM to produce high energy dense lithium metal phosphate battery cathode of tuned particle size.

[0016] The iron source in step (a) may be an iron ore, iron ore tailing, iron ore concentrate, tailing or by product typically obtained from a mineral deposit or aggregate that can be processed through conventional iron extraction techniques. Typically, the selected material contains at least one mineral selected from the group consisting of hematite, magnetite, goethite, and siderite.

[0017] Where the iron source is an iron ore, it must be chemically treated or purified to extract silicon and aluminium based impurities deleterious to battery cathode properties, conveniently by a combination of alkali and acid treatment steps to provide a residue containing a higher proportion of iron containing minerals than the iron ore. The silicon and aluminium based impurities may be extracted in conjunction or the silicon and aluminium based impurities may be extracted sequentially. Extraction of Si and Al gangue impurities is conducted to avoid the negative effects of these impurities on battery cathodes, battery capacity and cycle life.

[0018] An iron ore, purified as described above, may be reduced to form metallic iron which is processed to form an iron powder from which lithium iron phosphate can be manufactured by chemical processing. Carbon containing reductants or hydrogen may be used for the reduction.

[0019] Alternatively, the iron source in step (a) may be lithium iron phosphate (LFP) black mass comprising impurities such as carbon, binders, fine aluminium powders and / or fragments, fine stainless steel powder and / or fragments, fine copper powders and / or fragments, and other impurities such as mixed metal oxide cathode powders.

[0020] Lithium may be selectively leached from the LFP black mass by an acid mixture containing at least one acid selected from the group consisting of acetic acid, formic acid, succinic acid, carbonic acid and mixtures of these and an oxidising agent. The lithium containing solution is conveniently separated from an insoluble fraction including residual iron phosphates as an iron source, metal fragments, conductive carbon and binder(s). The residual iron phosphate may be calcined in an oxidizing atmosphere to remove the organic residues (e.g., conductive carbon and binders).

[0021] Optionally, where the iron source contains residual iron phosphate recovered from the lithium iron phosphate (LFP) black mass, is heated to selectively leach metals from the metal fragments.

[0022] Step (b), converting the treated iron source to produce iron phosphate cathode active material precursor (pCAM), may further comprise the steps of: (i) adding the iron source to a mixed acid solution comprising phosphoric acid, oxidising agent and mineral acid other than phosphoric acid; (ii) optionally heating the mixed acid solution; and (iii) separating insoluble iron phosphate pCAM from the mixed acid solution. The separated iron phosphate pCAM may then be dried to form hydrated iron phosphate. Hydrated iron phosphate may further be calcined in an oxidising atmosphere, a step which removes any residual organic material present, to form anhydrous iron phosphate. The mixed acid solution may be recycled for converting further iron source to iron phosphate and may be purified, for example by ion exchange, solvent exchange or selective precipitation, to remove dissolved impurities from the iron source.

[0023] The iron source, where containing acid insoluble impurities, is digested, preferably under ambient pressure at temperature below 100°C or hydrothermal digestion, in the mixture of phosphoric acid and mineral acid to form an iron (II) phosphate solution prior to conversion to solid iron phosphate pCAM. Iron phosphate pCAM is precipitated by progressive addition of oxidising agent to the iron (II) phosphate solution. The mixed acid solution is recycled for converting further iron source to iron phosphate and may be purified, for example by ion exchange, solvent exchange or selective precipitation, to remove dissolved impurities from the iron source.

[0024] Alternatively, step (b), converting the treated iron source to produce iron phosphate cathode active material precursor (pCAM), may further comprise the steps of: (i) digesting the iron source in oxalic solution to form a mixed solution of iron (II) oxalate and iron (III) oxalate, optionally at ambient pressure and temperature below 100°C or hydrothermally under pressure and temperature below 300°C , optionally at a molar ratio of oxalic acid to iron source higher than 1.3;(ii) adding oxidising agent, optionally hydrogen peroxide, to the mixture of iron (II) oxalate and iron (III) oxalate to form a soluble iron (III) oxalate solution; (iii) separating undigested residual iron source and impurities from the iron (III) oxalate solution; (iv) adding a phosphorus source to the iron (III) oxalate solution to form an iron phosphate solution, optionally at a ratio of phosphorus to iron in the iron phosphate solution greater than or equal to 1; (v) separating an insoluble fraction from the iron phosphate solution to form a purified iron phosphate solution; and (vi) drying the purified iron phosphate solution to form amorphous iron phosphate pCAM powder. The iron phosphate pCAM powder may be calcined in an oxidising atmosphere to form anhydrous iron phosphate pCAM.

[0025] Iron phosphate pCAM may be converted into energy dense lithium metal phosphate (LiFexM1-xP) battery cathode, the process comprising the following steps: (a) adding water, lithium, phosphorus and optionally at least one transition metal precursor to said iron source to form a stoichiometric suspension of an LiFexM1-xP precursor; (b) wet grinding said LiFexM1-xP precursor suspension in the presence of a carbon precursor for mechanochemical activation to form an LiFexM1-xP precursor slurry; (c) drying the LiFexM1-xP precursor slurry to produce a LiFexM1-xP precursor powder or cake; and (d) calcining the dried LiFexM1-xP precursor in an inert atmosphere to form LiFexM1-xP cathode powder, optionally at temperature in the range 450°C to 900°C.

[0026] Preferably, the at least one transition metal precursor, such as manganese dioxide, is present in the range 0 wt% to 99 wt% (x=0.1 to 1) in the stoichiometric suspension depending on the type of LiFexM1-xP being produced.

[0027] The carbon precursor is selected from the group consisting of sucrose, glucose and water soluble polymers.

[0028] Desirably, the LiFexM1-xP cathode powder is used to tune particle size of LiFexM1-xP cathode, the process comprising the steps of: (a) grinding the LiFexM1-xP cathode powder in the presence of an activating solution of lithium and phosphorus; (b) drying the activated LiFexM1-xP cathode powder; and (c) calcining the dried activated LiFexM1-xP cathode powder in an inert atmosphere to produce size tuned LiFexM1-xP cathode powder, preferably at temperature between 600 and 900°C.

[0029] The activating solution of lithium and phosphorus may conveniently be prepared by adding lithium (Li) and phosphorus (P) salts to water. The ratio of Li:P in the solution containing Li and P is preferably stoichiometric (equal to 1) or preferably >1. The amount of Li and P is preferably from 0.001 molar wt% to 10 molar wt% of the LiFexM1-xP in the cathode powder.

[0030] The LiFexM1-xP particle size may be tuned to between 50 nm and 1 μm The density of LiFexM1-xP cathodes following tuning is preferably from 1.5 g / cc to 2.8 g / cc.

[0031] The processes as described above are also applicable to iron sources, other than iron ore, such as pure or impure iron sources such as iron powder, sponge iron, synthetic iron oxides, iron salts etc.

[0032] The processes as described above enable production of lithium iron metal phosphate cathode materials from iron sources including abundant iron ore (and its derivative materials whether concentrates or tailings) or the black mass from lithium battery recycling. Such cathode materials contain low levels of impurities, an optimised particle size and an optimised energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Further features of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not beunderstood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

[0034] Figure 1 is a flowsheet for purifying iron ore as part of a process for producing a lithium iron phosphate cathode material according to a first embodiment of the process of the present invention.

[0035] Figure 2 is a flowsheet for producing a iron phosphate precursor (iron phosphate pCAM) from a purified iron source, which may contain soluble impurities, such as purified iron ore from the process of Figure 1 as part of a process for producing a lithium iron phosphate cathode material according to a second embodiment of the process of the present invention.

[0036] Figure 3 is a flowsheet for producing an iron phosphate precursor (iron phosphate pCAM) from a purified iron source, which may contain insoluble impurities, such as purified iron ore from the process of Figure 1 as part of a process for producing a lithium iron phosphate cathode material according to a third embodiment of the process of the present invention.

[0037] Figure 4 is a flowsheet for producing an iron phosphate precursor (iron phosphate pCAM) from a purified iron source, which may contain soluble impurities, such as purified iron ore from the process of Figure 1 as part of a process for producing a lithium iron phosphate cathode material according to a fourth embodiment of the process of the present invention.

[0038] Figure 5 is a flowsheet for producing lithium iron phosphate cathode material from the iron phosphate precursor (iron phosphate pCAM) produced according to the process of the embodiments illustrated in any of Figures 2 to 4. DESCRIPTION OF PREFERRED EMBODIMENTS

[0039] Below is described a process for producing a iron lithium metal phosphate cathode material from an iron source comprising the steps of: (a) chemically treating the iron source to provide a residue enriched in iron- bearing materials relative to the iron source; (b) converting the treated iron source to produce iron phosphate cathode active material precursor (pCAM); and(c) converting the iron phosphate pCAM to produce high energy dense lithium metal phosphate battery cathode.

[0040] In a first embodiment, iron ore as one example of an iron source is purified and converted to high energy dense lithium metal phosphate battery cathode. By “iron ore” is intended an iron ore, iron ore tailing, iron ore concentrate, tailing or by product typically obtained from a mineral deposit or aggregate that can be processed through conventional iron extraction techniques. Typically, the selected material contains at least one mineral selected from the group consisting of. hematite, magnetite, goethite, and siderite. The phosphorus content of the iron ore is not of importance to the process as described below. Further, the iron ore may be high grade or low grade.

[0041] In other embodiments, an iron source may be selected, without limitation, from a range of other iron sources such as iron powder, sponge iron, synthetic iron oxides, recycled battery waste etc.

[0042] Chemical purification of raw iron ore is selective towards the removal of gangue impurities. In particular, the process offers selective extraction of gangue impurities where the Si and Al impurities in the iron ore can be extracted in conjunction or sequentially during the chemical purification process. Other undesirable impurities are also extracted to varying degrees together with the Si and Al impurities.

[0043] The chemical purification process preferably involves thermal activation of the impurities present in the iron ore with an alkali and the subsequent leach of activated impurities in an acidic medium. The advantage of this method is an ability to selectively extract Si and Al gangue impurities from iron ore. Here, Si and Al gangue impurities can be extracted in conjunction or separately. The present disclosure also describes a process to recover the selectively extracted Si and Al impurities that can form valuable by-products for different end use applications. As a result, low-grade iron ores (including tailings) with high Si and Al content can be upgraded to be suitable for use as an iron source to produce lithium metal phosphate cathode materials.

[0044] The process to purify the iron ore as iron source for lithium metal phosphate cathode materials comprises a number of steps as follows.

[0045] 1)The iron ore is preferably ground to below 5 mm in size before the alkali activation of the impurities. The size of the ground iron ore is preferably from 1 µm to <5 mm. The iron ore grinding may be dry phase or wet phase milling.

[0046] 2)The ground iron ore is mixed with an alkali solution (e.g., NaOH, KOH or LiOH) to completely wet the iron ore with alkali. The concentration of alkali solution is between 5% to 90 w / w%, optionally 10% to 70 % w / w. Higher concentration of alkali is desirable to reduce the energy required to drive the water in subsequent impurity activation stage. The formation of a wet mixture of iron ore with alkali is advantageous for proper activation of Si and Al gangue impurities in the iron ore. However, the dry mixing of iron ore with alkali can also be conducted. The mass of alkali used is varied based on the impurity content in iron ore. Typically, the alkali content varies from 0.5% to 50% to the mass of the iron ore.

[0047] 3)The alkali-iron ore mixture is then thermally treated in a furnace to activate impurities in the ore before chemical leaching. Here, the temperature of treatment is varied from 20oC to 1000oC. Similarly, the time of treatment is from a few min to few hours, for example 4 hours.

[0048] 4) The activated ore is then washed with water to remove the residual alkali from the ore. The temperature of washing water can be from room temperature to 100oC. The water solution can be demineralized water, reverse osmosis (RO) water or any other contaminant free water source.

[0049] 5)The activated ore is then reacted with diluted mineral acid solution (e.g., HCl, H2SO4, HNO3) to extract the activated impurities from the ore. In one embodiment, the reaction temperature is conveniently in the range 20oC to 100oC under ambient pressure for impurity extraction though hydrothermal treatment under pressure, in an autoclave at temperature below 300°C may be used in another embodiment. Si and Al impurities form soluble species in the acidic leach solution while the iron ore remains largely undissolved. Specifically, the pH of the acidic solution is tuned for selective extraction of Si and Al based impurities. The pH of the acidic solution may be controlled between pH 0 – 3 when Si and Al impurities are extracted in conjunction and the pH may be controlled between pH 1.5 – 6 when Si and Al impurities are extracted separately. The amount of Si and Al impurities extracted can be optimised by varying the level of alkali activation and the conditions of acid leaching. Acidic leach may, for example, be conducted for 15 minutes to 4 hours.

[0050] 6) After the leaching step, the iron ore is separated from the leach solution. Different solid-liquid separation processes such as filtration, centrifugation or any other separation techniques can be used. The Si and Al impurities in the acidic solution can be further extracted by neutralizing the acid and converted into valuable by-products.

[0051] 7) Post processing of the iron ore for impurities extraction involves different washing steps based on the selective extraction of Si and Al impurities from the ore. a) Si and Al are extracted in conjunction- In such embodiments, the post processing steps desirably involve of the acid treated ore fromstep 6 with de-ionised water to remove the residual impurities in the ore. The water washed ore can be further washed with salt solution (e.g., ammonium, NH4Cl or other alkali metal salts like LiCl, Li2SO4, KCl etc.) to further remove the residual impurities. Typically, washing for 1-3 times is adequate to remove the entrained impurities. The extracted Si and Al impurities in the acidic leach solution is recovered by neutralising the acidic solution and can be converted into valuable by-products. b) Si and Al are extracted separately- After the selective extraction of Al the Si based impurities are extractedusing an alkali solution (e.g., NaOH solution). The removal of Si using alkali solution is desirably conducted at temperature 20C to 300°C, for example room temperature 120°C, under either ambient pressure or above atmospheric pressure for a defined period. The concentration of alkali solution can be from 5% to 90% w / w, optionally 10% to 70% w / w. The Si removed ore is then subjected to the post processing wash cycles involving de-ionized water (DI water) to remove residual impurities. The water washed ore can be further washed with salt solution (e.g., ammonium, NH4Cl or other alkali metal salts like LiCl, Li2SO4, KCl etc.) to remove the residual impurities. Typically, washing 1-3 times is adequate to remove the entrained impurities. Furthermore, the Al impurities in the acidic leach solution is extracted by neutralising the acid solution and be converted into valuable by-products.

[0052] In some embodiments, the purified iron ore may be further reduced to form purified iron powders. Such purified iron powders are a substitute for the iron ore as the iron source for producing iron phosphate pCAM or lithium metal phosphate cathodematerials. Different iron ore reduction technologies as known in the art can be implemented to form purified iron powder.

[0053] Iron source, whether purified iron ore or iron powder in steps

[0009] to

[0011] are converted to produce iron phosphate cathode precursor (pCAM) before conversion to lithium metal phosphate cathode materials. The conversion to iron phosphate pCAM is advantageous where further polishing of purified iron ore is required to produce lithium metal phosphate cathodes.

[0054] Preferred embodiments include two alternative processes for conversion of an iron source, as above exemplified, to iron phosphate pCAM precursor.

[0055] A first conversion process for synthesis of iron phosphate (FePO4) pCAM from the iron source comprises the following steps: a) Adding the iron source to a solution of phosphoric acid, oxidising agent (e.g., H2O2) and a mixed mineral acid solution (comprising e.g., HCl, H2SO4, H3NO3 etc). Here, the presence of both the mineral acid and oxidising agent in phosphoric acid is important while the sequence of materials addition is of lesser significance. The molar ratio of phosphoric acid to iron source is preferably greater than 1 whereas the mineral acid concentration in the phosphoric acid may be varied from 0.1% to 25% depending on the iron source and impurities present. In preferred embodiments, the target pH of the mixed acid solution is preferably <2. b) Progressively adding extra oxidising agent (e.g., hydrogen peroxide) to the mixture in step a) and heating as required to convert the iron source to iron phosphate. Depending on the iron source, an external heat source may or may not be required. Upon reaction, the conversion of iron source into iron phosphate is indicated by the formation of white or pinkish white suspension. Iron phosphate can be formed within minutes to a few hours of reaction time. In preferred embodiments, the progressive addition of oxidising agent is important for the complete conversion process and to tune the reaction time. c) Separating the insoluble product, i.e., iron phosphate pCAM from the mixed acid solution. Different separation technologies such as filtration, centrifugation, sedimentation etc. may be selected for separating the insoluble fractions. Theremaining mixed acid solution after filtration can be recycled back to step a) for further conversion of iron source into iron phosphate. d) The residue iron phosphate pCAM product is washed multiple times to remove the remaining acid solution and then dried to from a hydrated iron phosphate pCAM. Different drying technologies such as spray drying, freeze drying, thin film evaporation etc. can be utilized. e) The hydrated iron phosphate pCAM product from step d) may be further calcined in oxidising atmosphere (conveniently of air or oxygen) to form anhydrous iron phosphate pCAM.

[0056] In some embodiments, small amounts of base (e.g., NH4OH, NaOH etc.) may be added before step c) of the first conversion process to improve the recovery of iron phosphate pCAM product.

[0057] In some embodiments, the iron source in step a) of the first conversion process is digested at elevated temperatures to form a solution of iron source before conversion to iron phosphate (FePO4) in step b). In this embodiment, the digestion occurs in the absence of the oxidising agent in step a). In one embodiment, the digestion temperature may be conducted under ambient pressure typically below 100oC. However, the digestion may be conducted hydrothermally under pressure at temperatures up to 300°C.

[0058] The digestion process is preferred when the iron source contains impurities typically insoluble in the acid mixture. The insoluble impurities in the acid mixture may be removed using a range of different separation technologies such as filtration, centrifugation, sedimentation etc. The digestion of iron source typically forms a solution of iron (II) phosphate (Fe3(PO4)2) at pH <2 together with other soluble phosphates. The iron phosphate (FePO4) pCAM product is then conveniently obtained by progressively adding oxidising agent to precipitate as the solid iron phosphate. The iron phosphate pCAM is recovered by separating the precipitated iron phosphate from the mixed acid solution followed by the washing steps. In some cases, addition of a small amounts of base may be required to enhance the recovery of iron phosphate.

[0059] In some embodiments, the recycled mixed acid solution from step c) of the first conversion process is further purified. The purification process removes the dissolved impurities from iron source in the remaining mixed acid solution. Differentpurification processes such as ion exchange (IX), solvent exchange (SX) or selective precipitation etc. may be used depending on the nature of dissolved impurities remaining in the mixed acid solution.

[0060] In some embodiments, the first conversion process to synthesise iron phosphate (pCAM) may also be used to purify iron phosphate product obtained from recycled lithium iron phosphate (LFP) black mass. In such embodiments, the process to purify iron phosphate product obtained from recycled LFP black mass involves the following steps: 1. Selective oxidative leaching of lithium from recycled LFP black mass at elevated temperatures in the presence of acetic acid (or formic acid or their mixtures) and oxidising agent (e.g., hydrogen peroxide). The stoichiometric ratio of acetic acid to the recycled LFP is preferably higher than 1. The oxidative leaching temperature is desirably maintained above 50oC. Here, oxidative leaching is an exothermic process and may not require an external heating source. 2. Separating the leached lithium solution from the solids in the recycled black mass. Different separation technologies such as filtration, centrifugation, sedimentation etc. may be used for separating the insoluble fractions. Typically, the insoluble fractions are composed of residual iron phosphate mixed with metal fragments such as Fe, Al, Cu etc., conductive carbon, and binders. Further washing of the impure iron phosphate using deionised (DI) water may be required to remove the residual lithium solution. 3. Adding the impure iron phosphate to a mixed acid solution of phosphoric acid and mineral acid (e.g., HCl, H2SO4, H3NO3 etc). The pH of the mixed acid is preferably maintained below 2. 4. Heating the mixture in step 3 to selectively leach the undesirable metal fragments and impurities such as Al, Cu, Ni, Co etc. Here, the Fe metal fragments will be converted into iron phosphate during the reaction. The temperature for the impurity leaching can be under atmosphere below 100oC or under pressure below 300oC. 5. Separating the insoluble iron phosphate pCAM from the acid mixture. Different separation technologies such as filtration, centrifugation, sedimentation etc. may be used for separating the insoluble fractions. Further washing of the impure iron phosphate using DI water to remove the residual acid solution.6. The iron phosphate pCAM product from step 6 may contain the fractions of conductive carbon and / or binders. These impurities are conveniently removed by calcining the iron phosphate pCAM in a furnace under oxygen atmosphere.

[0061] In some embodiments, the lithium containing solution from separation step 2 above is desirably further purified and converted into lithium salts such as lithium acetate, Li2CO3, LiOH etc. as required.

[0062] A second conversion process to synthesise iron phosphate (FePO4) pCAM from an iron source comprises the steps of: 1) Digesting the iron source in oxalic acid solution at elevated temperature to form a mixed suspension of iron (II) / (III) oxalate. Preferably, the molar ratio of oxalic acid to iron source is higher than 1.3. The mixed iron (II) / (III) oxalate suspension may have a small portion of undigested iron source and other impurities. 2) Adding oxidising agent (e.g., H2O2) to the mixture of iron (II) / (III) oxalate to form a soluble iron (III) oxalate solution. Here, the majority of impurities in the iron source remains as insoluble species. 3) Separating the undigested residual iron source and impurities from the iron (III) oxalate solution. Different separation technologies such as filtration, centrifugation, sedimentation etc. may be selected for separating the insoluble fractions. 4) Adding phosphorus source to the iron (III) oxalate solution to form the iron phosphate solution. Different phosphorus sources such as phosphoric acid, monoammonium phosphate, diammonium phosphate etc. may be used. The ratio of phosphorus to iron in iron phosphate solution is preferably 1:1 (i.e., stoichiometric) or >1 (i.e., higher than stoichiometric). 5) Removing the insoluble fractions formed after adding phosphorus source from the iron phosphate solution. Different separation technologies such as filtration, centrifugation, sedimentation etc. may be selected for separating the insoluble fractions.6) Drying the purified iron phosphate solution to form amorphous iron phosphate pCAM. Different drying technologies such as spray drying, freeze drying, thin film evaporators etc. can be utilized.

[0063] The amorphous iron phosphate powder from step 6) may be further calcined in oxidising atmosphere (conveniently air or oxygen) to form anhydrous iron phosphate pCAM.

[0064] In some embodiments, the iron (III) oxalate solution from separation step 3) of the second conversion process is further polished to remove trace impurities. Different purification processes such as ion exchange (IX), solvent exchange (SX) or selective precipitation etc. may be selected for this purpose depending on the nature of trace impurities in the iron (III) oxalate solution.

[0065] In some embodiments, the iron phosphate solution from step 5) of the second conversion process can be further polished to remove the trace impurities. Different purification processes such as ion exchange (IX), solvent exchange (SX) or selective precipitation etc. may be selected depending on the nature of trace impurities in the iron phosphate solution.

[0066] Purified iron oxides and iron phosphate precursors, including those produced as described in the above embodiments, may be converted into energy dense lithium iron metal phosphate (LiFexM1-xP) battery cathode. LiFexM1-xP can be produced from iron phosphate by a process comprising the following steps: a) adding water, lithium, phosphorus, and other transition metal precursors as required to the iron phosphate pCAM (or purified iron oxide) to form a stoichiometric suspension of LiFexM1-xP precursor. Here, the percentage of transition metal precursors other than iron may be from 0% -99% (i.e., x= 0.1 to 1) depending on the type of LiFexM1-xP being produced. The typical formulation of lithium iron phosphate (LFP or LiFe1M0P) will have only iron phosphate as the transition metal precursor while that for lithium metal phosphate cathodes such as lithium manganese iron phosphate (LMFP) will also have an input of manganese precursor, such as manganese manganese dioxide or manganese oxalate, in addition to the iron phosphate. In the case of LMFP, the molar ratio of Mn:Fe may be between 0 and 9.b) wet grinding stoichiometric LiFexM1-xP precursor suspension in presence of carbon precursor (e.g., sucrose, glucose, water soluble polymers etc.) for mechanochemical activation and form the LiFexM1-xP precursor slurry. c) drying the LiFexM1-xP precursor slurry to produce LiFexM1-xP precursor powder or cake. The present invention will not be limited due to the drying technologies employed and drying techniques such as spray drying, freeze drying, thin film evaporators etc. can be utilised. d) calcining the dried LiFexM1-xP precursor in an inert atmosphere to form the LiFexM1-xP cathode powder. The calcining temperature to produce LiFexM1-xP cathode is preferably from 450oC to 900oC.

[0067] In some embodiments, LiFexM1-xP precursor from step (d) above is used to tune the particle size of LiFexM1-xP cathode. The process for tuning the particle size comprises the steps of: (a) grinding the LiFexM1-xP cathode powder from step (d) in the presence of a solution containing Li and P thus forming a slurry having solid content 5% to 50% w / w. The presence of the Li and P solution during grinding activates the LiFexM1-xP for the size tuning process. Wet grinding of the LiFexM1-xP powder is preferred. In one embodiment, the solution of Li and P is formed by mixing lithium carbonate in phosphoric acid solution though there are other possibilities. For example, Li and P solutions may be formed from lithium di-hydrogen phosphate, lithium hydrogen phosphate, lithium orthophosphate, lithium hydroxide etc. In preferred embodiments, the addition of a solution of Li and P to the LiFexM1-xP LiFexM1-xP powder during grinding is important for controlling the particle size of the LiFexM1-xP crystals of the cathode. The presence of Li and P in activated LiFexM1-xP increases the crystal size of the LiFexM1-xP crystals. The presence LiFexM1-xP of Li and P in activated LiFexM1-xP acts as a flux during sintering of the LiFexM1-xP LiFexM1-xP crystals thus increasing the particle size of the LiFexM1-xP cathode. Preferably, the ratio of Li:P in the Li and P solution is stoichiometric (1:1) or >1, for example in the range 1:5. The content of Li an d P may be from0.001 to 10 molar wt% of the LiFexM1-xP cathode powder for tuning the particle size; (b) drying the activated LiFexM1-xP after grinding. Preferably, spray drying is used but drying is not limited by technology. Other drying techniques including vacuum drying, freeze drying, thin film evaporation and so on may be used to yield the Li and P activated LiFexM1-xP cathode; and (c) calcining the activated LiFexM1-xP cathode from step (b) in an inert atmosphere to produce size tuned LiFexM1-xP cathode. The calcination temperature for producing the size tuned LiFexM1-xP cathode is preferably between 600°C and 900°C. Different inert gases, such as argon, nitrogen or argon / H2 mixtures etc., may be used for the inert atmosphere. Different calcination techniques, such as rotary furnace, fixed bed furnace, fluidized bed reactors etc. may be used for producing size tuned LiFexM1-xP cathode.

[0068] The size of the LiFexM1-xP cathode crystals may be tuned from 50 nm to 500 nm. The density of the resulting LiFexM1-xP electrodes can be from 1.5 g / cc to 2.8 g / cc.

[0069] In some embodiments, LiFexM1-xP from step (c) or step (d) is further ground to produce final LiFexM1-xP cathode. The grinding process can be ring milling, jet milling or any size reduction techniques.

[0070] Embodiments of the invention will be more fully understood from the following examples. Example 1 Purification of Iron Ore with Selective Extraction of Si and Al in Conjunction

[0071] The iron ore was ground to below 100 µm before the activation of impurities using an alkali (NaOH). The ground iron ore was then mixed with the alkali solution. The mass of alkali used was 10% of the mass of iron ore. The concentration of alkali was 50% w / w NaOH solution. The Si and Al impurities in the iron ore were activated using alkali (e.g., sodium hydroxide) via thermal treatment in a furnace. In this example, the temperature for the thermal treatment was set at 700oC and the time for thermal treatment was 1 hr. Here, the mass of alkali used for activation and temperature of thermal treatment can be varied to alter the extraction amounts of Si and Al from the ore.

[0072] Once the activation was completed, the alkali activated ore was washed with DI water to remove residual alkali in the impurity activated ore. The impurity activated ore was then treated using diluted acid solution. Here, diluted nitric acid (H3NO3) solution was used in this example. Other mineral acids such as HCl or H2SO4 solution can also be used for the acid treating process. Here, the pH of the acid solution was adjusted to 0.0 pH to remove Si and Al in conjunction. The acid treatment was conducted at 90oC for 1 hr. The purified ore was separated using filtration and washed with DI water 3 times to remove impurities. The purified ores can also be separated using other methods such as centrifugation, gravity settling etc. Here, effective washing with DI water is important to remove residual impurities in the ore. The acidic liquor contained the dissolved Si and Al impurities. The dissolved Si and Al impurities in acid were precipitated by neutralising the acid solution. Ammonia solution was preferred as the neutralising agent. Other neutralising agents can also be used to precipitate the dissolved Si and Al impurities. Example 2

[0073] The iron ore was ground below 100 µm before the activation of impurities using an alkali (NaOH). The ground iron ore was then mixed with the alkali solution. The mass of alkali used was 10% of the mass of iron ore. The concentration of alkali was 50% w / w NaOH solution. The Si and Al impurities in the iron ore were activated using alkali (e.g., sodium hydroxide) via thermal treatment in a furnace. The temperature of the thermal treatment was set at 700oC and the time for thermal treatment was 1 hr. Here, the mass of alkali used for activation and temperature of thermal treatment can be varied to alter the extraction amounts of Si and Al from the ore.

[0074] Once the activation was completed, the alkali activated ore was washed with DI water to remove residual alkali in the impurity activated ore. The impurity activated ore was then treated using diluted acid solution. In this example, the diluted nitric acid (H3NO3) solution was used in this example. Other mineral acids such as HCl, H2SO4 etc can also be used for the acid treating process. Here, the pH of the acid solution was adjusted to pH=3 to selectively extract Al from iron ore. The acid treatment was conducted at 90oC for 1 hr. The Al removed ore was separated using filtration and washed multiple times with DI water to remove residual impurities. The Al removed ores can also be separated using other methods such as centrifugation, gravity settling etc.The Al in the acid solution was selectively precipitated by neutralising the acid solution using ammonia solution.

[0075] To remove the residual Si from the ore, the Si containing ore after Al extraction was treated using NaOH solution at 90oC for 2 hr. Here, 50% w / w NaOH solution was used to extract the residual Si from the ore. After Si removal, the ore was filtered and washed multiple times using DI water to remove residual impurities.

[0076] Results for the Si and Al extraction are provided in the Table below: Sample_Description Fe(%) Al2O3(%) SiO2(%) P(%)ORE- Before purification 54.5 3.87 7.57 0.0504

[0077] a. Iron powder: The iron powder was reacted with 2 molar access of phosphoric acid in the presence of oxidising agent (hydrogen peroxide) and mineral acid (HCl) to prepare iron phosphate precursor. In this example, pH of the acid mixture was maintained <2. Briefly, 23.0 g of 85% phosphoric acid and 1 ml of 30% HCl solution was added to 200 ml of DI water. 5.5 g of iron powder was then added to the acid solution. Hydrogen peroxide (50% w / w) was added drop by drop to the resulting solution. This initiates the exothermic reaction and increases the temperature of the reaction. The addition of hydrogen peroxide accelerates the conversion of iron powder to iron phosphate. After a few minutes, white precipitate of iron phosphate is formed. Hydrogen peroxide is continuously added until all iron is converted to iron phosphate. Once the reaction is completed, the iron phosphate was separated using vacuum filtration and washed multiple times to purify the iron phosphate. The filtrate acid can be recycled for another batch of reaction by adjusting the concentration of phosphoric acid. The iron phosphate can be further dried and calcined at 600oC to form anhydrous iron phosphate. Example 4

[0078] b. Iron powder with soluble impurities: The iron powder with soluble impurities (e.g., Al, Cu) was reacted with 2 molar access of phosphoric acid in the presence of oxidising agent (hydrogen peroxide) and mineral acid (HCl) to prepare ironphosphate precursor. In this example, the pH of the acid mixture was maintained <2. Briefly, 23.0 g of 85% phosphoric acid and 1 ml of 30% HCl solution was added to 200 ml of DI water. 5.5 g of iron powder was then added to the acid solution. Hydrogen peroxide (50% w / w) was added drop by drop to the resulting solution. This initiates the exothermic reaction and increases the temperature of the reaction. The addition of hydrogen peroxide accelerates the conversion of iron powder to iron phosphate. After a few minutes, white precipitate of iron phosphate is formed. Hydrogen peroxide is continuously added until all iron is converted to iron phosphate. Once the reaction is completed, the iron phosphate was separated using vacuum filtration and washed multiple times to purify the iron phosphate. The filtrate acid can be further polished and recycled for another batch of reaction by adjusting the concentration of phosphoric acid. In one embodiment, the iron phosphate can be further dried and calcined at 600oC to form anhydrous iron phosphate. Example 5

[0079] c. Iron powder with in-soluble impurities: The iron powder with insoluble impurities (e.g., Si, carbon etc.) was reacted with 2 molar access of phosphoric acid and mineral acid (HCl). In this example, the pH of the acid mixture was maintained <1. Briefly, 23.0 g of 85% phosphoric acid and 2 ml of 30% HCl solution was added to 200 ml of DI water. 5.5 g of iron powder was then added to the acid solution. The mixture was digested at 100oC until all the iron was dissolved to form Fe3(PO4)2 solution. The Fe3(PO4)2 solution was separated from insoluble fractions by vacuum filtration. Hydrogen peroxide (50% w / w) was then added drop by drop to the resulting solution and the pH of the solution was adjusted to 2 by adding ammonia solution. The addition of hydrogen peroxide and ammonia accelerates the conversion to iron phosphate (FePO4) illustrated by formation of white precipitate of iron phosphate. Hydrogen peroxide is continuously added until all Fe3(PO4)2 is converted to FePO4. Once the reaction is completed, the iron phosphate was separated using vacuum filtration and washed multiple times to purify the iron phosphate. The filtrate acid can be further polished and recycled for another batch of reaction by adjusting the concentration of phosphoric acid. The iron phosphate can be further dried and calcined at 600oC to form anhydrous iron phosphate. Example 6

[0080] d. Iron oxide: The iron oxide was reacted with 2 molar access of phosphoric acid in the presence of oxidizing agent (hydrogen peroxide) and mineral acid (HCl) to prepare iron phosphate precursor. Briefly, 23.0 g of 85% phosphoric acid and 1 ml of 30% HCl solution was added to 200 ml of DI water. 15.9 g of iron oxide powder was then added to the acid solution. 10 ml of hydrogen peroxide (50% w / w) was added to the resulting solution. The resulting solution was heated to 95oC under reflux until all iron oxide is converted to iron phosphate. Once the reaction is completed, the iron phosphate was separated using vacuum filtration and washed multiple times to purify the iron phosphate. The filtrate acid can be recycled for another batch of reaction by adjusting the concentration of phosphoric acid. Example 7

[0081] e. Recycled LFP battery black mass: Briefly, 23.0 g mixture of 85% phosphoric acid and 30% HCl acid was added to 200 ml of DI water. The amount of HCl added to the phosphoric acid solution was controlled to maintain the pH of acid mixture to <1. 15 g of LFP black mass was then added to the acid solution and the resulting suspension was heated at 90oC to initiate the dissolution of the LFP black mass. Once the LFP black mass was completely dissolved, the residual insoluble impurities in leached LFP black mass solution was separated to obtain a solution of LFP black mass. The pH of the leached solution was adjusted to 2 and hydrogen peroxide (50% w / w) was added drop by drop to the resulting solution. The addition of hydrogen peroxide initiates the precipitation of iron phosphate pCAM from the leached LFP solution. The formation of iron phosphate pCAM is indicated by the formation of white precipitate solids. Hydrogen peroxide is continuously added until all iron is converted to iron phosphate. Iron phosphate pCAM was separated from the leached solution and washed multiple times to purify the iron phosphate. The remaining leached solution was further processed to extract lithium chemicals. The iron phosphate can be further dried and calcined at 600oC to form anhydrous iron phosphate. Example 8

[0082] f. Purification of iron phosphate from recycled LFP black mass: Briefly, 15 g LFP black mass was added to a solution of acetic acid and hydrogen peroxide solution (50% w / w) was added slowly to selectively extract lithium from the LFP black mass. The reaction is exothermic and the temperature of the reaction was maintained at 70°C. Once all lithium was extracted, the residual iron phosphate with impurities wasseparated from lithium solution using vacuum filtration. The impure iron phosphate with soluble impurities (e.g., Al, Cu) was then reacted with 2 molar access of phosphoric acid in the presence of oxidising agent (hydrogen peroxide) and mineral acid (HCl). In this example, the pH of the acid mixture was maintained <2. Briefly, 23.0 g of 85% phosphoric acid and 1 ml of HCl solution was added to 200 ml of DI water. Hydrogen peroxide (50% w / w) was added to the resulting solution and pH was adjusted to 2. Once the reaction is completed, the iron phosphate was separated using vacuum filtration and washed multiple times to purify the iron phosphate. The filtrate acid can be further polished and recycled for another batch of reaction by adjusting the concentration of phosphoric acid. The iron phosphate can be further dried and calcined to form anhydrous iron phosphate. Example 9

[0083] a. Purified iron oxide: Briefly, 25 g of oxalic acid dihydrate and 15.9 g of the purified iron ore was added to DI water. The resulting suspension was heated at 100oC for 4 hrs to completely digest the iron ore. Then, the solution was cooled, and hydrogen peroxide was added until all iron II oxalate was dissolved to for iron III oxalate solution. The resulting iron III oxalate solution was filtered to remove the insoluble impurities. 11.5 g of 85% phosphoric acid was added to the iron III oxalate solution to form iron phosphate solution. The iron phosphate solution was then dried to form amorphous iron phosphate powder. The amorphous iron phosphate powder was calcined in air at 700oC to form anhydrous iron phosphate pCAM. Example 10

[0084] b. Iron powder: Briefly, 25 g of oxalic acid dihydrate and 5.5 g of the iron powder was added to DI water. The resulting suspension was heated at 100oC for 4 hrs to completely digest the iron powder. Then, the solution was cooled, and hydrogen peroxide was added until all iron II oxalate was dissolved to for iron III oxalate solution. The resulting iron III oxalate solution was filtered to remove the insoluble impurities. 11.5 g of 85% phosphoric acid was added to the iron III oxalate solution to form iron phosphate solution. The iron phosphate solution was then dried to form amorphous iron phosphate powder. The amorphous iron phosphate powder was calcined in air at 600oC to form anhydrous iron phosphate pCAM. Example 11

[0085] The LFP precursor was first prepared by using the purified iron oxide as the iron precursor. Briefly, purified iron oxide was added to a solution of lithium and phosphorus to produce a slurry of LFP precursor. The lithium and phosphorous solution were prepared by adding lithium carbonate to phosphoric acid solution. As obtained LFP precursor was then wet ground using 0.5 mm zirconia bead at 2000 rpm for mechanochemical activation and spray dried to form LFP precursor powder. The LFP precursor powder was calcined in nitrogen atmosphere at 650oC to form the primary LFP. Then, a solution of lithium and phosphorus was prepared by mixing lithium and phosphorus precursors in DI water at ambient conditions. Here, lithium carbonate and phosphoric acid were used as the lithium and phosphorus precursors. Other sources of lithium and phosphorus can be utilized to form the precursor solution; however, lithium carbonate or lithium hydroxide was preferred to eliminate the impurities in the solution. The molar ratio of the lithium to phosphorus in the solution was Li>P. The lithium and phosphorus solution were then added to the primary LFP cathode together with the sucrose and ground to form a slurry. The resulting slurry was then dried to form Li and P activated primary LFP powder. Finally, the Li and P activated primary LFP was calcined in nitrogen atmosphere at 740oC to form the final LFP powder.

[0086] The purified iron oxide may be partially substituted using manganese precursors, such as manganese dioxide or manganese oxalate, to form lithium manganese iron phosphate (LMFP). The molar ratio of Mn:Fe may be varied from 0 to 9. Example 12

[0087] In this example, lithium iron phosphate (LFP) is produced from iron phosphate pCAM. The LFP precursor was first prepared by using iron phosphate as the iron precursor. Briefly, phosphate was added to a suspension of lithium to produce a slurry of LFP precursor. The lithium suspension was prepared by adding lithium carbonate to DI water solution. As obtained LFP precursor was then wet ground using 0.5 mm zirconia bead at 2000 rpm for mechanochemical activation and spray dried to form LFP precursor powder. The LFP precursor powder was calcined in nitrogen atmosphere at 650oC to form the primary LFP. Then, a solution of lithium and phosphorus was prepared by mixing lithium and phosphorus precursors in DI water at ambient conditions. Here, lithium carbonate and phosphoric acid were used as the lithium and phosphorus precursors. Other sources of lithium and phosphorus can beutilized to form the precursor solution; however, lithium carbonate or lithium hydroxide was preferred to eliminate the impurities in the solution. The molar ratio of the lithium to phosphorus in the solution was Li>P. The lithium and phosphorus solution were then added to the primary LFP cathode together with the sucrose and ground to form a slurry. The resulting slurry was then dried to form Li and P activated primary LFP powder. Finally, the Li and P activated primary LFP was calcined in nitrogen atmosphere at 740oC to form the final LFP powder.

[0088] In one embodiment, the purified iron oxide was substituted using manganese precursors such as manganese phosphate to form lithium manganese iron phosphate (LMFP). The molar ratio of Mn:Fe varied from 0 to 9.

[0089] In one embodiment, the lithium and phosphorus solution can also be added after grinding the primary LFP in the bead mill. The presence of Li and P precursor during grinding activates the LFP and Li and P acts as a flux during the calcination step.

[0090] The processes as described above enable production of lithium iron metal phosphate cathode materials from iron sources including abundant iron ore (and its derivative materials whether concentrates or tailings) or the black mass from lithium battery recycling. Such cathode materials contain low levels of impurities, an optimised particle size and an optimised energy density.

[0091] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

CLAIMS 1. A process for converting an iron source to lithium metal phosphate battery cathode comprising the steps of: (a) optionally chemically treating the iron source to provide a residue enriched in iron-bearing materials relative to the iron source; (b) converting the iron source to produce iron phosphate cathode active material precursor (pCAM); and (c) converting the iron phosphate pCAM to produce high energy dense lithium metal phosphate battery cathode of tuned particle size.

2. The process of Claim 1, wherein the iron source in step (a) is an iron ore, optionally containing at least one mineral selected from the group consisting of. hematite, magnetite, goethite, and siderite.

3. The process of Claim 1 or 2, wherein the iron source is chemically treated to extract silicon and aluminium based impurities to provide a residue containing a higher proportion of iron containing minerals than the iron source.

4. The process of claim 3, wherein silicon and aluminium based impurities are extracted in conjunction.

5. The process of claim 3, wherein silicon and aluminium based impurities are extracted sequentially.

6. The process of any one of the preceding claims, wherein silicon and aluminium based impurities are extracted by a combination of alkali and acid treatment steps.

7. The process of any one of claims 3 to 6, wherein the iron source is ground and mixed with an alkali; and the iron ore-alkali mixture is thermally treated to activate impurities contained within the iron ore.

8. The process of claim 7, wherein the iron source is washed to remove residual alkali from the thermally treated and activated iron source.

9. The process of claim 8, wherein the washed activated iron source is leached with a dilute acid solution to extract activated impurities from the thermally treated and activated iron ore.

10. The process of claim 9, wherein pH of the dilute acid solution is controlled to enable selective extraction into solution of silicon and aluminium based impurities from the thermally treated and activated iron source leaving an acid treated iron source.

11. The process of claim 10, wherein pH is controlled to between 0 and 3 to extract silicon and aluminium based impurities in conjunction.

12. The process of claim 10, wherein pH is controlled between 1.5 and 6 to separately extract silicon and aluminium based impurities.

13. The process of claim 11 or 12, wherein said acid treated iron source is separated from the acid solution and washed in at least one washing step to remove residual water soluble impurities.

14. The process of claim 13, wherein said acid treated iron source is washed to form purified iron source, washing being by at least one of deionised water and optionally a salt solution, said salt solution optionally containing at least one of ammonia, ammonium chloride and an alkali metal salt.

15. The process of claim 13 or 14, wherein said acid treated iron source is separated from the acid solution and alkali leached for removal of silicon-based impurities forming a purified iron source.

16. The process of claim 15, wherein said alkali treated residue is washed in at least one washing step by at least one of deionised water and optionally a salt solution, said salt solution optionally containing at least one of ammonia, ammonium chloride and an alkali metal salt.

17. The process of any one of the preceding claims, wherein purified iron source is reduced to form metallic iron which is processed to form an iron powder.

18. The process of claim 2, wherein said purified iron ore is reduced by a reductant selected from the group consisting of carbon containing reductants and hydrogen.

19. The process of any one of the preceding claims, wherein the silicon and aluminium- based impurities from the acid solution are recovered either together or separately by neutralising the acid solution.

20. The process of claim 1, wherein the iron source in step (a) is lithium iron phosphate (LFP) black mass comprising impurities such as carbon, binders, fine aluminium powders and / or fragments, fine stainless steel powder and / or fragments, fine copperpowders and / or fragments, and other impurities such as mixed metal oxide cathode powders.

21. The process of claim 20, wherein the lithium is selectively leached from the LFP black mass by an acid mixture containing at least one acid selected from the group consisting of acetic acid, formic acid, succinic acid, carbonic acid and mixtures of these; and an oxidising agent.

22. The process of claim 21, wherein the lithium containing solution is separated from the insoluble fraction from the LFP black mass, said insoluble fraction including residual iron phosphates as an iron source, metal fragments, conductive carbon and binder(s).

23. The process of claim 22, wherein the residual iron phosphate is calcined in an oxidizing atmosphere to remove the organic residues (e.g., conductive carbon and binders) 24. The process of claim 23, wherein the lithium containing solution is further purified and converted to form a selected lithium salt.

25. The process of claim 1, wherein step (b) comprises the steps of: (i) adding the iron source to a mixed acid solution comprising phosphoric acid, oxidising agent and mineral acid other than phosphoric acid; (ii) optionally heating the mixed acid solution; and (iii) separating insoluble iron phosphate pCAM from the mixed acid solution.

26. The process of claim 25, wherein mineral acid concentration in phosphoric acid is in the range 0.01wt% to 25wt%.

27. The process of claim 25 or 26, wherein target pH of the mixed acid solution is less than 2.

28. The process of any one of claims 25 to 27, wherein said oxidising agent is added progressively during step (a).

29. The process of any one of claims 25 to 28, wherein said separated insoluble iron phosphate pCAM is washed to remove residual solution.

30. The process of any one of claims 25 to 29, wherein said separated iron phosphate pCAM is dried to form hydrated iron phosphate.

31. The process of claim 30, wherein said hydrated iron phosphate is calcined in an oxidising atmosphere to form anhydrous iron phosphate.

32. The process of any one of claims 25 to 31, wherein an amount of alkaline solution is added prior to separating insoluble iron phosphate from the solution.

33. The process of any one of claims 25 to 32, wherein the iron source, where containing acid insoluble impurities, is digested in the mixture of phosphoric acid and mineral acid to form an iron (II) phosphate solution prior to conversion to solid iron phosphate pCAM.

34. The process of claim 33, wherein said digestion is conducted at ambient pressure at temperature below 100°C; or said digestion is conducted hydrothermally at above atmospheric pressure and temperature below 300°C.

35. The process of claim 33 or 34, wherein iron phosphate pCAM is precipitated by progressive addition of oxidising agent to the iron (II) phosphate solution.

36. The process of any one of claims 25 to 35, wherein said mixed acid solution is recycled for converting further iron source to iron phosphate.

37. The process of claim 36, wherein said recycled mixed acid solution is purified to remove dissolved impurities from the iron source.

38. The process of claim 37, wherein said recycled mixed acid solution is purified by a process selected from the group consisting of ion exchange, solvent exchange and selective precipitation depending on the nature of the dissolved impurities remaining in the mixed acid solution.

39. The process of any one of claims 19 to 38, wherein the iron source, where containing residual iron phosphate recovered from the lithium iron phosphate (LFP) black mass, is heated in said mixed phosphoric acid to selectively leach metals from the metal fragments.

40. The process of claim 1, wherein step (b) comprises the steps of: (i) digesting the iron source in oxalic solution to form a mixed solution of iron (II) oxalate and iron (III) oxalate; (ii) adding oxidising agent, optionally hydrogen peroxide, to the mixture of iron (II) oxalate and iron (III) oxalate to form a soluble iron (III) oxalate solution;(iii) separating undigested residual iron source and impurities from the iron (III) oxalate solution; (iv) adding a phosphorus source to the iron (III) oxalate solution to form an iron phosphate solution; (v) separating an insoluble fraction from the iron phosphate solution to form a purified iron phosphate solution; and (vi) drying the purified iron phosphate solution to form amorphous iron phosphate pCAM powder.

41. The process of claim 40, wherein the molar ratio of oxalic acid to iron source in step (a) is higher than 1.

3.

42. The process of claim 41 or 42, wherein the phosphorus source is selected from the group consisting of phosphoric acid, monoammonium phosphate, diammonium phosphate and mixtures of these.

43. The process of any one of claims 40 to 42, wherein the ratio of phosphorus to iron in the iron phosphate solution of step (d) is greater than equal to 1.

44. The process of any one of claims 40 to 43, wherein the iron phosphate pCAM powder of step (f) is calcined in an oxidising atmosphere to form anhydrous iron phosphate pCAM.

45. The process of any one of claims 40 to 44, wherein the iron (III) oxalate solution of step (c) or the iron phosphate solution of step (d) is polished to remove trace impurities, optionally by a process selected from the group consisting of ion exchange, solvent exchange and selective precipitation depending on the nature of trace impurities in the iron (III) oxalate solution.

46. The process of any one of the preceding claims, wherein an iron source including iron phosphate pCAM is converted into energy dense lithium iron metal phosphate (LiFexM1-xP) battery cathode, the process comprising the following steps: (a) adding water, lithium, phosphorus and optionally at least one transition metal precursor to said iron source to form a stoichiometric suspension of an LiFexM1-xP precursor;(b) wet grinding said LiFexM1-xP precursor suspension in the presence of a carbon precursor for mechanochemical activation to form an LiFexM1-xP precursor slurry; (c) drying the LiFexM1-xP precursor slurry to produce a LiFexM1-xP precursor powder or cake; and (d) calcining the dried LiFexM1-xP precursor in an inert atmosphere to form LiFexM1- xP cathode powder.

47. The process of claim 46, wherein the at least one transition metal precursor is present in the range 0 wt% to 99 wt% (x=0.1 to 1) in the stoichiometric suspension depending on the type of LiFexM1-xP being produced.

48. The process of claim 46 or 47, wherein said carbon precursor is selected from the group consisting of sucrose, glucose and water soluble polymers.

49. The process of any one of claims 46 to 48, wherein said dried LiFexM1-xP precursor is calcined at temperature in the range 450°C to 900°C.

50. The process of any one of claims 46 to 49, wherein the LiFexM1-xP cathode powder is used to tune particle size of LiFexM1-xP cathode, the process comprising the steps of: (a) grinding the LiFexM1-xP cathode powder in the presence of an activating solution of lithium and phosphorus; (b) drying the activated LiFexM1-xP cathode powder; and (c) calcining the dried activated LiFexM1-xP cathode powder in an inert atmosphere to produce size tuned LiFexM1-xP cathode powder.

51. The process of claim 50, wherein the solution of lithium and phosphorus is prepared by adding lithium (Li) and phosphorus (P) salts to water.

52. The process of claim 51, wherein the ratio of Li:P in the solution containing Li and P is stoichiometric (equal to 1) or preferably >1.

53. The process of any one of claims 50 to 52, wherein the amount of Li and P is from 0.001 molar wt% to 10 molar wt% of the LiFexM1-xP in the cathode powder.

54. The process of any one of claims 50 to 53, wherein calcining temperature is between 600 and 900°C and the inert atmosphere comprises at least one gas selected from the group consisting of argon, nitrogen, hydrogen and mixtures thereof.

55. The process of any one of claims 46 to 54, wherein the LiFexM1-xP particle size is tuned to between 50 nm and 500 nm.

56. The process of any one of claims 46 to 55, wherein the density of LiFexM1-xP cathodes following tuning is from 1.5 g / cc to 2.8 g / cc.

57. The process of any one of claims 46 to 56, wherein the LiFexM1-xP cathode powder is further grind following calcining.

58. The process of any one of claims 1 or 3 to 57, wherein the iron source is other than iron ore and selected from the group consisting of pure or impure iron sources such as iron powder, sponge iron, synthetic iron oxides and iron salts.

Images