A method for regeneration of a cathode active material

Abstract

A method for regeneration of a cathode active material with controllable tuning of particle size from a solid electrode material containing lithium metal phosphate and impurities comprising oxidative leaching of a mixture containing solid electrode material, at least one organic acid and an oxidising agent for selectively solubilising lithium, iron and phosphorus, and manganese where present in the solid electrode material, preferentially to impurities into a precursor solution; separating solid residue containing insoluble impurities from the precursor solution; and regenerating lithium metal phosphate cathode active materials from the precursor solution with controllable tuning of particle size.

Description

A METHOD FOR REGENERATION OF A CATHODE ACTIVE MATERIALTECHNICAL FIELD

[0001] The present invention relates to a method for regeneration of a cathode active material.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] Due to unprecedented growth of lithium-ion batteries (or LIBs) in recent years, a need has arisen for more economical and efficient technology for the extraction of valuable minerals from spent or waste batteries. This need is reflected by an increase in research activity devoted to this subject. However, the recycling of LIBs is still problematic and the overall material recovery efficiency for current recycling technologies is less than 50% by weight. Cathode active materials account for more than 50% of the materials cost for LIBs and are considered the most valuable component of an LIB from a resource recovery perspective.

[0004] Most current recycling processes fall under the umbrella of ‘reagent recovery’ because the materials, with sufficient purity, can be re-used not just for re-synthesising the original cathode materials, but also in a range of other applications. The recycling methods for the recovery of valuable minerals from spent LIBs involves a combination of physical and chemical separation technologies. The recovered materials from spent LIBs after comminution are subjected to a range of physical separation processes. This results in a concentration of electrode coatings in the fine fractions of material. A concentration of plastics casing materials and metal foils occurs in the coarse fractions. The fine fraction is referred to as ‘black dust’, ‘black metal dust’ or ‘black mass’ and comprises electrode coating materials (e.g. metal oxides and carbon). The carbon can be further separated from metal oxides by froth flotation, which exploits the hydrophobicity of carbon to separate it from the more hydrophilic metal oxides (or mixed metal dust).

[0005] Pyrometallurgy and hydrometallurgy are the most common methods to extract the valuable minerals like lithium, cobalt, nickel, manganese etc. from the recycled mixed metal dust. Pyrometallurgy uses a high temperature furnace to smelt and reduce the component metal oxides to an alloy (e.g. of Co, Cu, Fe and Ni). It is particularly advantageous for the recycling of general consumer LIBs. Hydrometallurgical extraction uses aqueous solutions to leach the desired metals from the cathode material. It is the most common approach to extract valuable minerals from recycled black metal dust and uses a combination of reagents, such as sulphuric acid and hydrogen peroxide. The concentration of leaching acid, time, solution temperature, solid-to-liquid ratio and the addition of a reducing agent are optimized for efficient extraction of minerals.

[0006] Direct recycling is an alternative method where the recycled mixed metal dust can be incorporated into a new cathode electrode with minimal changes to the crystal morphology of the active material. In general, the lithium content in the cathode needs to be replenished to compensate for losses due to degradation of the material during battery use. There are also potential issues with the flexibility of direct recycling to handle metal oxides of different compositions. Direct recycling is also challenged by feedstocks that are unknown or poorly characterized. The direct recycling route is also sensitive to contamination by other metals, such as aluminium and copper, and can result in poor electrochemical performance.

[0007] Lithium iron phosphate (LiFePC , “LFP”) is a commonly used battery cathode material providing better electrochemical performance, temperature stability, safety, and cycle life. The better electrochemical performance and improved safety aspects make LFPs suitable for use in electric vehicles, energy storage and a range of other applications. It is forecast that the use of LFP cathodes will continue to increase and will occupy a sizable portion of LIBs. Currently, the major focus is directed towards recovering economically valuable components like Co, Li, Ni and Mn from spent LIBs, while the recycling of LFP-based batteries has been neglected for economic reasons.

[0008] The LFP recycling processes to date involve numerous purification steps and conventionally used pyrometallurgical and hydrometallurgical approaches are not effective for recycling LFP cells due to the lower content of valuable minerals (e.g. Li). Although some direct recycling methods and other cathode regeneration techniqueshave been reported, these methods either produce lower quality LFP cathodes or involve complicated processing steps.

[0009] Lithium manganese iron phosphate (LiFeMnPO4,”LMFP”) is a manganese doped or substituted LFP. Similar issues for recycling LFMP cathode materials arise as for LFP cathode materials.

[0010] Furthermore, volumetric energy density of LFP and LMFP cathode materials is greatly influenced by physical properties. For example, although LFP has a bulk density of 3.6 g / cc, 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, differently sized LFP with reasonable carbon content is desired for 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. Particularly with the increased uptake of LFP in electric vehicles and energy storage applications, the desire for high density LFP with good performance is ever increasing.

[0011] Sintering temperature and conductive carbon content is generally altered to tune the particle size of LFP and LFMP cathodes. Increasing the temperature increases the particle size while increasing the carbon content decreases the particle size. Control over LFP and LFMP 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 the battery life. The current LFP and LFMP production process is generally not effective to produce high density LFP and LMFP cathodes and this need remains to be met.

[0012] The present invention has been developed against this background.SUMMARY OF INVENTION

[0013] In a first aspect, the present invention provides a method for regeneration of a cathode active material with controllable tuning of particle size from a solid electrode material containing lithium metal phosphate and impurities comprising:(a) oxidative leaching of a mixture containing solid electrode material, at least one organic acid and an oxidising agent for selectively solubilising lithium, iron and phosphorus, and manganese where present in the solid electrode material, preferentially to impurities into a precursor solution;(b) separating a solid residue containing insoluble impurities from the precursor solution to form a purified precursor solution; and(c) regenerating lithium metal phosphate cathode active materials from the precursor solution with controllable tuning of particle size.

[0014] The lithium metal phosphate would typically have formula LiFexMi-xPO4, where M is a transition metal element or a combination of transition metal elements and x is between 0.01 and 1. The lithium metal phosphate is conveniently selected from the group consisting of lithium iron phosphate (LiFePC ) and lithium manganese iron phosphate (LiMnFePC ).

[0015] Preferably, the amount of organic acid, the amount of oxidising agent and oxidative leaching time for selectively solubilising lithium, iron and phosphorus, and manganese where present in the solid electrode material, preferentially to impurities are determined as a function of the quantity of impurities in the solid electrode material. The solid electrode material may contain up to about 90 wt% impurities but may be significantly lower in some cases, for example in the range 1 to 10 wt%.

[0016] Advantageously, the at least one organic acid is selected from the group consisting of oxalic acid, citric acid and ascorbic acid. Preferably, the at least one organic acid is oxalic acid. Where lithium manganese iron phosphate is treated, oxalic acid is used in admixture with at least one of ascorbic acid and citric acid. Preferably, a molar ratio of the at least one organic acid to lithium metal phosphate is between 1.0 and 4.0 and a molar ratio of oxidising agent to the lithium metal phosphate is 0.1 to 4.0.

[0017] Oxidative leaching may have temperature controlled below about 100°C under ambient pressures though higher temperatures and pressures may be selected by the user. Oxidative leaching may be conducted for up to 24 hours but leaching time is preferably less than 2 hours and may be on the order of minutes. Further oxidising agent may be added to the mixture during the oxidative leach.

[0018] The above described oxidative leach or digestion process is highly selective for solubilisation of lithium, iron and phosphorus and manganese where present. The impurities are substantially insoluble and remain in the solid phase though any minor quantity of solubilised impurities may be washed from the solid phase during separation from the precursor solution.

[0019] If required, the precursor solution may be treated by a further process, for example by ion exchange using a suitable ion exchange resin, to remove trace impurities.

[0020] In some embodiments, the precursor solution may be further treated by subjecting to a reducing environment to form the solid precipitate of iron (II) oxalate and a solution of lithium and phosphorus. Iron (II) oxalate precipitate may be separated from the precursor solution. Similarly, the resulting lithium and phosphorous solution may be treated by a further process, for example using suitable ion exchange resin, to remove trace impurities or to extract valuable elements such as lithium and produce a lithium salt, for example being selected from the group consisting of LiH2PO4, U3PO4, LiOH and U2CO3.

[0021] A lithium iron phosphate cathode material typically requires a determined Li:Fe:P stoichiometry, with a target Li:Fe:P ratio being preferably between 1 :1 :1 and 1.05:1 :1. The method may therefore comprise adjusting the Li:Fe:P stoichiometry of the precursor solution by addition of a salt containing at least one of Li, Fe and P. The salt may contain two or all of these, for example lithium dihydrogen phosphate. The following description is directed to a lithium iron phosphate though the same principles would also apply to a lithium iron manganese phosphate or lithium metal phosphate to be used as a cathode active material.

[0022] Iron (Fe) may be adjusted by adding an Fe source. Examples of a suitable Fe source may include, without limitation, a salt selected from the group consisting of iron (III) oxalate, ferri-oxalate complexes, ferric citrate, ferric acetate and iron sulphate. Examples of ferri-oxalate complexes include ammonium ferrioxalate and lithium ferrioxalate. Solid iron (II) oxalate from a prior iron precipitation step, as described above, may be added as Fe source.

[0023] Phosphorus (P) may be adjusted by adding a P source. Examples of a suitable P source may include, without limitation, phosphoric acid, ammonium phosphate, lithium dihydrogen phosphate and lithium hydrogen phosphate.

[0024] Lithium (Li) may be adjusted by adding an Li source which may, without limitation, be selected from the group consisting of lithium carbonate, lithium hydroxide, lithium metal and lithium dihydrogen phosphate.

[0025] The precursor solution, desirably with target Li:Fe:P stoichiometry, is dried, preferably spray dried, to form a lithium iron phosphate precursor powder. In some embodiments, the precursor solution may be a slurry, for example including a solid source such as iron (II) oxalate from the iron precipitation step described above. This slurry is also dried to form a lithium iron phosphate precursor powder.

[0026] Following drying, the lithium iron phosphate precursor powder may be calcined in an inert atmosphere, preferably at calcining temperature between 400 and 700°C to produce the primary lithium iron phosphate powder. The inert atmosphere may comprise, without limitation on inert gas, at least one gas selected from the group consisting of argon, nitrogen, hydrogen and mixtures thereof.

[0027] Preferably, the primary lithium iron phosphate powder is ground in the presence of a carbon precursor to form the cathode active material. Wet grinding is preferred. As small a particle size as practicable is desired, with a particle size below 500 nm being an exemplary upper particle size limit.

[0028] Following grinding, the ground lithium iron phosphate material should be dried, preferably spray dried. The dried and ground lithium iron phosphate cathode material is then calcined, preferably at temperature between 600 and 900°C, in an inert atmosphere, for example containing an inert gas as above described. The calcination produces a final lithium iron phosphate cathode active material.

[0029] Advantageously, the primary lithium iron phosphate powder is contacted with a carbon precursor and an activating solution containing lithium and phosphorus which allows tuning, or control, of the particle size of the final lithium iron phosphate powder for use as cathode material. The ability to tune the particle size, particularly to increase the particle size, of the final lithium iron phosphate powder allows energy density to be increased. Contacting of primary lithium iron phosphate powder with the solution containing lithium and phosphorus may be conducted during or after grinding.

[0030] Tuning of final lithium iron phosphate particle size to a selected size, preferably in the range 50 nm to 500 nm, is optimised by controlling the concentration of Li and P in the solution containing lithium and phosphorus. Concentration of lithium and phosphorus is preferably in the range from 0.001 molar wt% to 10 molar wt%. Preferably, the ratio of Li:P in the solution containing lithium and phosphorus is stoichiometric or preferably >1 .

[0031] Following tuning, the selected lithium metal phosphate particle size is tuned to between 50 nm and 500 nm. Density of the lithium metal phosphate cathodes is from 1 .5 g / cc to 3.0 g / cc.

[0032] The solid electrode material may, for example, be sourced from a range of waste battery materials, for example as recycled black metal dust or black mass or waste solid electrode materials or off-spec solid electrode materials.

[0033] Another aspect of the invention comprises a method for tuning the particle size of lithium iron phosphate comprising:(a) preparing an activating solution containing lithium and phosphorus for controlling the particle size of a lithium iron phosphate;(b) contacting a lithium phosphate powder with the solution containing lithium and phosphorus in the presence of a carbon precursor; and(c) tuning the lithium metal phosphate particle size by controlling the concentration of lithium and phosphorus in the solution containing lithium and phosphorus which is contacted with the lithium phosphate powder.

[0034] The lithium metal phosphate may be derived from the method involving digestion as described above. The lithium metal phosphate may also be derived from a conventional manufacturing process, for example a process producing lithium iron phosphate.

[0035] As to the carbon precursor, a soluble carbon source such as sucrose or glucose is preferred.

[0036] The method for regenerating the cathode active material involves a simpler flowsheet than for prior cathode active material recycling technologies. The ability to tune the particle size of lithium metal phosphate cathode materials also allowsproduction of batteries with high energy density (or volumetric capacity) and better elevated temperature performance.BRIEF DESCRIPTION OF THE DRAWINGS

[0037] 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 be understood 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:

[0038] Figure 1 is a process flowsheet depicting a process for generating an LFP precursor solution from a cathode active material from a spent battery according to one embodiment of the present invention.

[0039] Figure 2 is a process flowsheet depicting a process for generating an LFP powder from the process depicted in Figure 1 .

[0040] Figure 3 is a process flowsheet depicting a process for producing a final LFP cathode material product with tuned particle size.

[0041] Figure 4 is an X-ray diffraction spectrum for regenerated LFP cathode material produced by the process according to embodiments of the present invention.

[0042] Figure 5 shows a galvanostatic charge and discharge cycle of the regenerated LFP cathode material at 0.1 C rate

[0043] Figure 6 shows a galvanostatic charge and discharge cycle of the regenerated LFP cathode from the waste LFP cathode materials from manufacturing process.DESCRIPTION OF PREFERRED EMBODIMENTS

[0044] In some embodiments, black metal dust is the solid electrode material treated to form lithium iron phosphate or lithium iron manganese phosphate. Lithium iron manganese phosphate is a lithium iron phosphate in which some iron is substituted by manganese, for example being doped by manganese.

[0045] In summary, the regeneration method involves the following steps:(a) oxidative leaching of a mixture containing solid electrode material, at least one organic acid and an oxidising agent for selectively solubilising lithium, iron and phosphorus, and manganese where present in the solid electrode material, preferentially to impurities into a precursor solution;(b) separating a solid residue containing insoluble impurities from the precursor solution to form a purified precursor solution; and(c) regenerating lithium metal phosphate cathode active materials from the precursor solution with controllable tuning of particle size. which will now be described in further detail below.

[0046] Recycled LFP black metal dust powder is added to a mixture containing oxalic acid solution and oxidising agent (e.g. hydrogen peroxide) to initiate the digestion of the recycled LFP black metal dust to form a precursor solution containing Li, Fe and P and, in other embodiments concerning LFMP, Mn also. Here, the sequence of materials addition is of lesser significance.

[0047] The presence of both the oxalic acid and oxidising agent is important to the digestion process and the formation of the Li, Fe and P containing precursor solution. The combination of oxalic acid and oxidising agent allows selective solubilisation of Li, Fe and P from the black metal dust powder.

[0048] The recycled LFP black metal dust may comprise different impurities not being limited to carbon, binders, fine aluminium powders and / or fragments, fine stainless steel powder and / or fragments and other impurities such as mixed metal oxide cathode powders. The fraction of the impurities can be from 0 wt% up to 90 wt%. However, these impurities remain either unreacted or in the form of insoluble components at the conclusion of the digestion step.

[0049] Thus, formation of the Li, Fe and P containing precursor solution may require only a single digestion step allowing a less complicated process than those currently known.

[0050] Depending on the levels of different impurities in the recycled black metal dust, the amount of oxalic acid, oxidising agent, temperature, and reaction time can be optimised for maximum removal of the impurities.

[0051] With regard to the amount of oxalic acid, the molar ratio of the oxalic acid to the LFP can be from 1.0 to 4.0. The molar ratio of the oxidising agent to the LFP can be from 0.1 to 4.0.

[0052] With regard to temperature, the digestion process is exothermic and generates heat such that no external heat is generally required to initiate the digestion process. This accelerates the digestion process though the temperature of digestion would typically be controlled below 100°C which may require cooling.

[0053] The digestion step can be conducted within a few minutes to 24 hours but, conveniently, in less than 2 hours.

[0054] In some embodiments, the recycled LFP black metal dust is pre-treated before digestion to further improve the removal of soluble impurities such as residual battery electrolytes or to enhance the hydrophilicity of the recycled black metal dust. Wetting agents such as surfactants, for example polyethylene glycol, may be added to enhance the hydrophilicity of the recycled black metal dust. Soluble impurities from the recycled black metal dust are removed by pre-treating with water or with an alkaline solution. Examples of alkaline solutions that may be used for the purpose include lithium hydroxide and sodium hydroxide.

[0055] In some embodiments, the LFP precursor solution is separated from the solid impurity fraction. Although already substantially pure due to selective solubilisation of lithium, iron and phosphorus, trace impurities may remain. Such trace impurities may be removed by a suitable polishing process, for example ion exchange involving an ion exchange resin. However, processes other than ion exchange could be used.

[0056] In some embodiments, the LFP precursor solution extracted from the recycled LFP black metal dust is further subjected to a reducing environment to form the solid precipitates of iron (II) oxalate and a solution of lithium and phosphorus. The reducing environment can be photo-induced, electrochemically induced or chemically induced. The solid iron (II) oxalate is then separated from the lithium and phosphorus containing solution. Different separation technologies such as filtration, centrifugation, sedimentation etc may be used for separating the iron (II) oxalate fractions. The liquor containing lithium and phosphorus is then purified to remove undesirable trace level impurities. Ion exchange processes using ion exchange resins may be applied for this step, if desired, though other options are available.

[0057] The separated lithium and phosphorus containing solution may be further processed to form lithium and phosphorus based chemicals such as LiH2PO4, LisPC , LiOH, Li2CO3, H3PO4 and so on.

[0058] In other embodiments, black metal dust (for example) may be treated to regenerate lithium manganese iron phosphate (LiMnFePC or LMFP). In such embodiments, the digestion mixture contains - as organic acid portion - a mixture of oxalic acid with other organic acids, in particular ascorbic acid and / or citric acid. With manganese present, it is possible to also preferentially solubilise Mn from the impurities.

[0059] The process for regenerating LMFP follows the same method as described above for LFP.

[0060] The particle size of cathode active material, whether LFP or LMFP, is tunable or controllable to optimise the energy density for battery use. In embodiments, the tuning method proceeds as follows with the LFP embodiment being taken for purposes of example.

[0061] The stoichiometry of the LFP precursor solution is adjusted to a target Li:Fe:P ratio of 1 :1 :1 to 1.05:1 :1 by adding additional amounts of Li, Fe and P. This step avoids the formation of impurity phases.

[0062] The Li:Fe: P stoichiometry may be adjusted by Li, Fe and / or P sources. It will be understood that Li, Fe or P salts or salts containing one or all of Li, Fe, P may be used for purposes of adjustment with it being desirable that such salts contain a minimum of cationic impurities. The following examples of Li, Fe and P sources are not intended to be limiting.

[0063] Required amounts of Li, Fe and P precursors are measured to adjust the Li:Fe:P stoichiometry of the precursor solution,. For example, Li2COs is used as Li precursor, iron (III) oxalate is used as Fe precursor and phosphoric acid is used as P precursor.

[0064] Iron (III) oxalate solution may be prepared by oxidation of iron (II) oxalate dihydrate by an oxidising agent, conveniently hydrogen peroxide in the presence of excess oxalic acid. By ‘excess’ is intended a higher than stoichiometric ratio of 1 :1 between iron and oxalate in iron (II) oxalate. Normally, iron (III) oxalate will have an iron to oxalate ratio of 1 :1 .5 or above but sometimes even below, like 1 :1.3 have been found to exist thus oxalic acid is preferably added.

[0065] In this embodiment, U2CO3 may be added to the lithium (III) oxalate solution together with phosphoric acid. This solution is then available for adjustment of the LFP precursor solution. It will be understood that other solution compositions for Li:Fe:P adjustment may be adopted.

[0066] In an alternative embodiment, the Fe source may be solid iron (II) oxalate which is added to the LFP precursor solution to form a slurry. Alternatively, the solid iron (II) oxalate may be combined with the purified lithium and phosphorus solution. The stoichiometry of the resulting LFP precursor solution is then adjusted - as described above - to form a stoichiometric LFP precursor solution to be directed to the following steps of the method.

[0067] The LFP precursor solution at target Li:Fe:P stoichiometry is then dried to form a powder which is calcined in an inert atmosphere to produce primary LFP cathode material. Preferably, spray drying is used as drying technology. Other drying options could be used including vacuum drying, freeze drying, thin film evaporation and so on. The calcination temperature for producing the primary LFP cathode material is optionally between 400 and 700°C. Different inert gases or gas mixtures, such as argon, nitrogen or Fh / argon mixtures and so on, may be used to form the inert atmosphere. Calcination may be conducted in any suitable vessel, for example rotary furnace, fixed bed furnace, fluidised bed reactors and so on.

[0068] The calcined primary LFP powder is then subjected to grinding in the presence of carbon precursor (e.g. a soluble carbon compound such as sucrose or glucose) and a tuning solution of lithium and phosphorus for tuning the final LFP particle size. Wet grinding of the primary LFP powder is preferred. The grinding media bead size may be selected between from 0.1 mm to 2 mm, dependent on desired LFP particle size (there being a direct relationship between bead size and LFP particle size), while the grinding time is, for example, 5 minutes to 5 hours to achieve a final primary particle size, for example below 500 nm.

[0069] The solution of lithium and phosphorus may be prepared in a number of ways. Typically, embodiments will comprise mixing of lithium and phosphorus precursors to form the solution containing lithium and phosphorus. Conveniently, lithium carbonate and phosphoric acid are respectively used as the lithium and phosphorus precursors. However, other lithium and phosphorus precursors may be used.

[0070] Following grinding, the solution (or slurry) containing primary LFP and additional lithium and phosphorus from the particle size tuning solution are dried, again preferably by spray drying. As described above, other drying technologies could be used. The product is a lithium and phosphorus activated primary LFP powder.

[0071] This primary LFP powder is calcined in an inert atmosphere to produce a final LFP powder. The calcination temperature is optionally between 600 and 900°C. The inert atmosphere is conveniently formed by an inert gas or gas mixture as described above.

[0072] As alluded to above, the addition of the tuning solution containing lithium and phosphorus to the primary LFP during grinding is important for tuning, i.e. controlling, the particle size, of the final LFP crystals. Increasing the amount of lithium (Li) and phosphorus (P) in the activated primary LFP increases the particle size of the final LFP crystals. Without wishing to be bound by theory, the presence of Li and P acts as a flux during sintering of the primary LFP particles thus increasing the particle size of the final LFP crystals. Preferably, the Li:P ratio of the tuning solution is stoichiometric or >1. The amount of Li and P may be from 0.001 molar wt% to 10 molar wt% of the primary LFP for tuning the final LFP particle size, preferably to between 50 and 500 nm. The density of the resulting LFP electrodes may be from 1 .5 g / cc to 3.0 g / cc.

[0073] In other embodiments, an activating solution containing lithium and phosphorus may be added after grinding but before drying.

[0074] In some embodiments, the LFP black metal dust may be replaced by waste LFP cathodes from a conventional manufacturing process. A conventional manufacturing process may involve producing LFP cathode materials from raw materials such as iron oxalate, iron phosphate, iron oxides and so on as known in the art of LFP battery manufacture. Furthermore, the particle size of preformed or commercially produced LFP may also be tuned using the method as described above. The commercial LFP cathode may then be subjected to grinding in the presence of carbon precursor and tuning solution containing lithium and phosphorus as described above.

[0075] In such an embodiment, the primary LFP cathode material may be produced using iron (II) oxalate dihydrate as the iron precursor. The iron (II) oxalate dihydrate may then be added to a solution for example comprising lithium carbonate and phosphoric acid. Alternatively, and again for example, the solution could contain lithiumphosphate and phosphoric acid. The grinding, activation, drying and calcining steps then proceed as described above.

[0076] Embodiments of the invention will be more fully understood from the following examples.Example 1

[0077] This example illustrates the regeneration process of LFP cathode from recycled LFP black metal dust according to embodiments of the present invention. Figs. 1 and 2 represent the schematic illustration of the production of an LFP precursor solution as well as conversion of the LFP precursor solution to a high quality LFP cathode with tunable particle size from the recycled black metal dust.

[0078] In summary, given the description above, the black metal dust containing LFP cathode materials and impurities from the battery recycling process was digested in oxalic solution containing oxidising agent, here hydrogen peroxide. In this embodiment, the molar ratio of oxalic acid to LFP was maintained at 2:1 ratio. The digestion process generates heat during the reaction, which increases temperature of the digestion mixture. The digestion temperature was controlled to 80°C. The time for digestion may be from 5 minutes to 2 hours.

[0079] Before the digestion process, a wetting agent or hydrophilic surfactant, e.g. polyethylene glycol, may be added to the black metal dust powder to enhance wettability of the black metal dust powder. Here the addition of polyethylene glycol solution or other wetting agents is optional and can be omitted from the process if the black metal dust has sufficient wettability.

[0080] Further hydrogen peroxide was progressively added to completely digest the LFP in black metal dust.

[0081] The resulting precursor solution, after such progressive addition of hydrogen peroxide, was then passed through a vacuum filtration step to remove the solid undigested materials.

[0082] The above process purifies the LFP precursor solution as shown in Table 1 .Table 1 Results of ICP Analysis of waste LFP and LFP Black Metal Dust

[0083] The stoichiometric ratio or Li:Fe:P ratio of the resulting LFP precursor solution, following filtration and separation of undigested material, was adjusted by adding a solution containing Li, Fe and P. In this embodiment, the required Li, Fe and P containing solution was prepared by oxidising iron (II) oxalate dihydrate in excess oxalic acid solution with hydrogen peroxide and then adding the required amount of Li and P, here by addition of phosphoric acid and lithium carbonate.

[0084] The stoichiometry adjusted LFP precursor solution was spray dried to form LFP precursor powder. The dried LFP precursor powder was then calcined in an inert atmosphere at 460°C to form a primary LFP powder.

[0085] The primary LFP powder was then wet ground in the presence of carbon source (e.g. sucrose) and a solution containing Li and P. The Li and P solution was prepared by adding lithium carbonate in phosphoric acid solution. Other suitable carbon sources may include glucose, fructose, saccharides and soluble polymers such as carboxymethyl cellulose, polyvinylalcohol and polyethylene glycols for example. The primary LFP powder was ground to ~250 nm.

[0086] The primary LFP with Li and P solution was then spray dried to form an Li and P activated primary LFP powder. The presence of both Li and P allowed control over the particle size of LFP crystals. The resulting powder was then calcined in an inert atmosphere at 740°C to form the final LFP powder. Figs. 4 and 5 respectively show the X-ray diffraction pattern and the galvanostatic charge / discharge cycles for regenerated LFP cathode material.Example 2

[0087] This example illustrates regeneration of LFP cathode material from the waste and / or by-product LFP from a conventional manufacturing process. In summary, the waste containing LFP cathode materials from the conventional manufacturing process was digested in a mixture containing oxalic acid and oxidising agent in solution. The molar ratio of oxalic acid to LFP was maintained at a 2:1 ratio. Again an exothermic process, the digestion temperature was controlled to 80°C. The time for digestion may be from 5 minutes to 2 hours.

[0088] Before the digestion process, a wetting agent or hydrophilic surfactant, e.g. polyethylene glycol, was added to the waste LFP powder to enhance wettability of the waste LFP powder. Here the addition of polyethylene glycol solution or other wetting agents is optional and can be omitted from the process if the waste LFP has sufficient wettability.

[0089] Further hydrogen peroxide was progressively added to completely digest the waste LFP with selective solubilisation of Li, Fe and P preferentially to impurities.

[0090] The resulting precursor solution, after such progressive addition of hydrogen peroxide, was then passed through a vacuum filtration step to remove the solid undigested materials.

[0091] The above process purifies the LFP precursor solution as shown in Table 1 .

[0092] The stoichiometric ratio or Li:Fe:P ratio of the resulting LFP precursor solution, following filtration and separation of undigested material, was adjusted by adding a solution containing Li, Fe and P. In this embodiment, the required Li, Fe and P containing solution was prepared by oxidising iron (II) oxalate dihydrate in excess oxalic acid solution with hydrogen peroxide and then adding the required amount of Li and P, here by addition of phosphoric acid and lithium carbonate.

[0093] The stoichiometry adjusted LFP precursor solution was spray dried to form LFP precursor powder. The dried LFP precursor powder was then calcined in an inert atmosphere at 460°C to form a primary LFP powder.

[0094] The primary LFP powder was then wet ground in the presence of carbon source (e.g. sucrose) and a solution containing Li and P. The Li and P solution was prepared by adding lithium carbonate in phosphoric acid solution. Other suitable carbon sources may include glucose, fructose, saccharides and soluble polymers for example as described above. The primary LFP powder was ground to ~250 nm.

[0095] The primary LFP with Li and P solution was then spray dried to form an Li and P activated primary LFP powder. The presence of both Li and P allowed control over the particle size of LFP crystals. The resulting powder was then calcined in an inert atmosphere at 740°C to form the final LFP powder. Fig. 6 shows the galvanostatic charge / discharge cycles for regenerated LFP cathode material.Example 3

[0096] This example illustrates tuning of the particle size of LFP cathode material by adding a lithium and phosphorus containing tuning solution during the grinding of primary LFP as described above. Here, the molar ratio of lithium and phosphorus in the tuning solution was adjusted to tune the LFP particle size.

[0097] The primary LFP was first prepared with iron (II) oxalate dihydrate as the iron precursor. Iron (II) oxalate dihydrate was added to a solution containing lithium and phosphorus to produce a slurry of LFP precursor. In this example, lithium and phosphorus containing solution was prepared by adding lithium carbonate to phosphoric acid solution. The LFP precursor slurry was then wet ground using 0.5mm zirconia beads at 2000 rpm for mechanochemical activation and spray dried to form LFP precursor powder.

[0098] The ground and dried LFP precursor powder was then calcined under a nitrogen gas atmosphere at 460°C to form the primary LFP.

[0099] Then a tuning solution containing lithium and phosphorus was prepared by mixing lithium and phosphorus precursors in deionised water under ambient conditions. Here, lithium carbonate and phosphoric acid were used as precursors though other options are available, for example as described above. Lithium carbonate or lithiumhydroxide, preferably battery grade or above, have the advantage of minimising impurities added to the powder. Molar ratio was Li>P. The lithium and phosphorus containing tuning solution was then added to the primary LFP cathode together with sucrose and ground to form a slurry.

[0100] 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 under a nitrogen atmosphere at 740°C to form the final LFP powder with a range of particle size achievable as shown in Table 2 below. Here the amount of Li and P was increased to increase the particle size. The dried Li and P from the tuning acts as a flux during calcination over a 1 hour calcination time.Table 2 Particle Size Tuning

[0101] It will be understood that the tuning solution could be added after grinding with a similar outcome. Similarly, the primary LFP can also be replaced by commercial LFP to tune the particle size.

[0102] 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

CLAIMS1 . A method for regeneration of a cathode active material with controllable tuning of particle size from a solid electrode material containing lithium metal phosphate and impurities comprising:(a) oxidative leaching of a mixture containing solid electrode material, at least one organic acid and an oxidising agent for selectively solubilising lithium, iron and phosphorus, and manganese where present in the solid electrode material, preferentially to impurities into a precursor solution;(b) separating solid residue containing insoluble impurities from the precursor solution; and(c) regenerating lithium metal phosphate cathode active materials from the precursor solution with controllable tuning of particle size.

2. The method of any one of the preceding claims, wherein the lithium metal phosphate has formula LiFexMi-xPO4, where M is a transition metal element or a combination of transition elements and x is between 0.01 and 1.

3. The method of claim 1 or 2, wherein the amount of organic acid, the amount of oxidising agent and oxidative leaching time for selectively solubilising lithium, iron and phosphorus, and manganese where present in the solid electrode material, preferentially to impurities are determined as a function of the quantity of impurities in the solid electrode material, the solid electrode material optionally comprising less than 90 wt% impurities.

4. The method of claim 3, wherein the at least one organic acid is selected from the group consisting of oxalic acid and citric acid, preferably oxalic acid.

5. The method of claim 4, wherein a molar ratio of the at least one organic acid to lithium metal phosphate is between 1 .0 and 4.0 and the molar ratio of oxidising agent to the lithium metal phosphate is 0.1 to 4.0.

6. The method of any one of the preceding claims, wherein oxidative leaching temperature is controlled below about 100°C.

7. The method of any one of the preceding claims, wherein oxidative leaching is conducted for up to 24 hours, preferably less than 2 hours.

8. The method of any one of the preceding claims, wherein further oxidising agent is added to the mixture during oxidative leach.

9. The method of any one of the preceding claims, wherein the lithium metal phosphate is selected from the group consisting of lithium iron phosphate (LiFePC ) and lithium manganese iron phosphate (LiMnFePC ).

10. The method of claim 9, as dependent from claim 3, wherein, when the lithium metal phosphate is lithium manganese iron phosphate (LiMnFePC ) the mixture contains oxalic acid and at least one of ascorbic acid and citric acid, oxidative leaching step (a) also solubilising manganese into the precursor solution.11 . The method of any one of the preceding claims, comprising pre-treatment for at least one of a) removing soluble impurities from the solid electrode material and b) increasing hydrophilicity of the solid electrode material.

12. The method of claim 11 , wherein the solid electrode material is washed with water or an alkaline solution to remove soluble impurities from the solid electrode material.

13. The method of claim 11 or 12, wherein a surfactant is added to the solid electrode material to increase hydrophilicity.

14. The method of any one of the preceding claims, wherein oxidative leaching step (a) is conducted under pressure, optionally at temperature above 100°C.

15. The method of any one of the preceding claims, wherein the precursor solution containing lithium, iron and phosphorus is treated to remove trace impurities present in the precursor solution.

16. The method of claim 15, wherein the precursor solution is subjected to ion exchange for removal of impurities.

17. The method of any one of the preceding claims, wherein the precursor solution is subjected to a reducing environment to precipitate iron, preferably as iron (II) oxalate, precipitated iron being separated from the precursor solution.

18. The method of claim 17, wherein the precursor solution following iron precipitation and containing Li and P is treated to remove remaining trace impurities, preferably by ion exchange.

19. The method of claim 17 or 18, wherein the purified precursor solution is further treated to produce a lithium salt whether or not containing phosphorus.

20. The method of claim 19, wherein the lithium salt is selected from the group consisting of I H2PO4, LisPC , LiOH and U2CO3.21 . The method of claim 19, wherein the precursor solution is treated to recover phosphoric acid.

22. The method of claim 17 or 18, comprising grinding, preferably wet grinding, of iron (II) oxalate with precursor solution to form a precursor slurry.

23. The method of any one of the preceding claims, the cathode regeneration process comprises adjusting the stoichiometry of the precursor solution containing lithium, iron and phosphorus to a target Li:Fe:P ratio by addition of at least one of Li, Fe and P to the precursor solution, optionally by addition of a salt containing at least one of Li, Fe and P.

24. The method of claim 23, wherein the target Li:Fe:P stoichiometry is 1 :1 :1 to 1.05:1 :1.

25. The method of claim 23 or 24, wherein Fe is adjusted by adding a Fe source selected from the group consisting of iron (III) oxalate, ferri-oxalate complexes, ferric citrate, ferric acetate and iron sulphate.

26. The method of claim 25, wherein said ferri-oxalate complex is selected from the group consisting of ammonium ferrioxalate and lithium ferrioxalate.

27. The method of any one of claims 23 to 26, as dependent from claim 17 or 18, wherein solid iron (II) oxalate from iron precipitation is added to the precursor solution to adjust Fe.

28. The method of claim 25, wherein an iron (III) oxalate solution is prepared by oxidation of iron (II) oxalate dihydrate by hydrogen peroxide in the presence of excess oxalic acid.

29. The method of any one of claims 23 to 28, wherein P is adjusted by adding a P source selected from the group consisting of phosphoric acid, ammonium phosphate, lithium dihydrogen phosphate and lithium hydrogen phosphate.

30. The method of any one of claims 23 to 29, wherein Li is adjusted by adding an Li source selected from the group consisting of lithium carbonate, lithium hydroxide, lithium metal and lithium dihydrogen phosphate.31 . The method of any one of claims 23 to 31 , wherein said the precursor solution or slurry is dried, preferably spray dried, to form a lithium metal phosphate precursor powder.

32. The method of claim 31 , wherein said precursor powder is calcined in an inert atmosphere to produce a primary lithium iron phosphate cathode material.

33. The method of claim 32, wherein calcining temperature is between 400 and 700°C and the inert atmosphere comprises at least one gas selected from the group consisting of argon, nitrogen, hydrogen and mixtures thereof.

34. The method of claim 32 or 33, comprising grinding of the primary lithium iron phosphate cathode material in the presence of carbon precursor and an activating solution containing lithium and phosphorus to controllably tune the particle size.

35. The method of claim 34, wherein said grinding is wet grinding.

36. The method of claim 34 or 35, wherein said grinding is conducted for time to achieve a primary lithium iron phosphate particle size below 500 nm.

37. The method of claim 36, wherein said ground lithium iron phosphate cathode material is dried, preferably spray dried.

38. The method of claim 37, wherein said dried and ground lithium iron phosphate cathode material is calcined in an inert atmosphere to produce a final lithium iron phosphate cathode material.

39. The method of claim 38, 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.

40. The method of any one of the preceding claims, wherein controllable tuning of the particle size of lithium metal phosphate comprises:(a) preparing an activating solution containing lithium and phosphorus for controlling the particle size of lithium metal phosphate;(b) contacting a lithium metal phosphate powder with the solution containing lithium and phosphorus in the presence of a carbon precursor; and(c) tuning the lithium metal phosphate particle size by controlling the concentration of lithium and phosphorus in the solution containing lithium and phosphorus which is contacted with the lithium phosphate powder.41 . The method of claim 40, wherein the solution of lithium and phosphorus is prepared by adding lithium and phosphorus salts in water.

42. The method of claim 41 , wherein the ratio of Li: P in the solution containing Li and P is stoichiometric or preferably >1 .

43. The method of any one of claims 40 to 42, wherein the amount of Li and P is from 0.001 molar wt% to 10 molar wt% of lithium metal phosphate for tuning the lithium metal phosphate particle size to a selected particle size.

44. The method of any one of claims 40 to 43, as dependent from claim 32, wherein the said lithium metal phosphate is the primary lithium iron phosphate powder following calcination.

45. The method of any one of the claims 40 to 44, wherein the said lithium metal phosphate is derived from the primary or final lithium iron phosphate produced by a conventional manufacturing process.

46. The method of any one of the claims 40 to 44, wherein the said lithium metal phosphate is lithium manganese iron phosphate.

47. The method of claim 40 to 46, wherein the said lithium metal phosphate is contacted with the solution containing lithium and phosphorus in the presence of carbon precursor during grinding.

48. The method of claim 47, wherein the said grinding is wet grinding.

49. The method of claim 48, wherein said grinding is conducted for time to achieve lithium metal phosphate particle size below 500 nm.

50. The method of claim 49, wherein said ground lithium metal phosphate cathode material is dried, preferably spray dried.51 . The method of claim 50, wherein said dried and ground lithium metal phosphate cathode material is calcined in an inert atmosphere to produce a final lithium metal phosphate cathode material.

52. The method of claim 51 , 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.

53. The method of claim 40 to 52, wherein the selected lithium metal phosphate particle size is tuned to between 50 nm and 1 pm, optionally 50 nm to 500 nm.

54. The method of claim 40 to 53, wherein the density of lithium metal phosphate cathodes resulting from the final lithium metal phosphate is from 1 .5 g / cc to 3 g / cc.

55. The method of any one of claims 40 to 55, wherein said carbon precursor is any soluble form of organic carbon precursor, preferably sucrose or glucose.

56. The method of any one of the preceding claims, wherein said solid electrode material is derived from a lithium metal phosphate battery.

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