WO2024182839A1

WO2024182839A1 - Recycling of battery metals

Info

Publication number: WO2024182839A1
Application number: PCT/AU2024/050171
Authority: WO
Inventors: Junnan LU; Kathryn Anne MUMFORD; Geoffrey Wayne STEVENS
Original assignee: University of Melbourne
Current assignee: University of Melbourne
Priority date: 2023-03-03
Filing date: 2024-03-01
Publication date: 2024-09-12
Anticipated expiration: 2025-09-03

Abstract

The present invention provides a method of producing a battery-grade precursor solution for production of a cathode material, the method comprising the steps of: providing a battery black-mass liquid leachate, said liquid leachate comprising one or more battery metals; adding an immiscible liquid solvent to said liquid leachate and performing liquid-liquid extraction to load said liquid solvent with the one or more battery metals; and subjecting the resulting loaded liquid solvent to stripping in at least one stripping unit; wherein stripping is performed using an aqueous stripping solution having a pH that extracts the one or more battery metals into the aqueous stripping solution to provide for said battery-grade precursor solution.

Description

RECYCLING OF BATTERY METALS FIELD OF THE INVENTION The present invention relates generally to a method of isolating battery metals from battery black-mass leachate, and more particularly to a method of producing a battery-grade precursor solution for production of a cathode material. BACKGROUND OF THE INVENTION Batteries are ubiquitous means of storing and providing electrical energy in a wide variety of devices, including electric vehicles, portable electronics, and renewable energy storage systems. As the demand for batteries increases, so does the need for efficient recycling processes aiming at "closing the loop" on the life cycle of battery metals. Recycling battery metals has become a main technology priority to minimise dependency from environmentally-tasking extraction processes and geopolitically sensitive access to mining sites. Battery metals are mainly concentrated in the cathode part of the battery, and can be recovered from spent batteries using combinations of mechanical, pyrometallurgical, and hydrometallurgical procedures. Recycling typically requires an initial physical shredding, sieving and magnetic separation of a spent battery. Those physical steps result in a fine fraction commonly referred to as "black-mass", mainly made of comminuted cathode material. Liberation of battery metals from the back-mass is typically achieved by acid leaching, resulting in multi-metal acid leachate solutions. To close the loop on the life cycle of battery metals it is therefore necessary to eventually isolate those metals from the acid leachate. Conventional procedures for isolating battery metals from those leachate solutions mostly involve fractional and selective chemical precipitation, membrane separation, liquid-liquid extraction and/or ion-exchange. While those procedures can achieve some degree of separation of the battery metals, they are not immune from carry-over of impurities from the leachate solution, and the separated fractions need further processing before the metals can effectively be used in the production of new battery cathodes. Also, conventional chemical extraction procedures still require extensive use of additional chemicals, adding to an already environmentally tasking recycle procedure. Accordingly, there is an opportunity for the development of more efficient and environmentally-friendly procedures for the extraction of battery metals from spent batteries. SUMMARY OF THE INVENTION The present invention provides a method of producing a battery-grade precursor solution for production of a cathode material, the method comprising the steps of: providing a battery black-mass liquid leachate, said liquid leachate comprising one or more battery metals; adding an immiscible liquid solvent to said liquid leachate and performing liquid- liquid extraction to load said liquid solvent with the one or more battery metals; and subjecting the resulting loaded liquid solvent to stripping in at least one stripping unit; wherein stripping is performed using an aqueous stripping solution having a pH that extracts the one or more battery metals into the aqueous stripping solution to provide for said battery-grade precursor solution. The method of the present invention proposes a sequence of liquid-liquid extraction and stripping steps, in which the extraction step is designed to achieve the initial transfer of all the battery metals from the black-mass leachate into one liquid solvent. Battery metals can then be selectively stripped off the loaded solvent by one or more stripping solutions at a pH tuned to target removal of one or more metals. Accordingly, the proposed method allows for the use of a single immiscible liquid solvent to achieve separation of multiple battery metals at once, as opposed to multiple solvents selected to target each metal separately. The proposed method therefore allows to recycle, purify, and concentrate battery metals from recycled spent batteries in one step using the same solvent. This can prevent solvent contamination, and avoiding the need for subsequent extraction and purification of battery metals from the extraction raffinate, which can simply be disposed. In some embodiments, stripping is performed in multiple stripping units, for example in a cascade of stripping units affording collection of multiple battery metal-enriched streams. This configuration ensures significant process efficiency and flexibility, in that the composition of downstream metal-enriched streams can be easily tuned by modulating the pH of the stripping solution(s). The composition of the metal-enriched streams can therefore be tailored to battery-grade specifications for direct production of cathode materials by simply acting on the pH of the stripping solutions. The composition of said multiple streams can also be advantageously controlled such that any of the streams can be combined pro rata for direct production of cathode materials. Advantageously, the battery metals can be isolated either as one or more solution streams of individual target metals or one or more solutions of mixed metals compositions in battery- grade stoichiometry. As such, the method allow for the continuous production of battery metal solutions that can be used for the direct production of cathode materials with no need for further manipulation. Also, the pH of the stripping solution(s) can be dynamically and adaptively modulated in accordance to varying formulations of the initial black-mass leachate to achieve and maintain desired formulations of the battery-grade precursor solutions. This allows for the continuous production of streams of recovered battery metals having target compositions that can be customised irrespective of the specific formulation of the leachate being treated. In some embodiments, stripping is performed in a cascade of at least two stripping units. This configuration allows for the continuous provision of one or multiple streams of battery- grade cathode precursor solutions having different compositions. The composition of any such stream can be tailored for production of cathode materials, or for downstream pro rata combination to form precursor solutions having a formulation tailored for production of cathode materials. The proposed extraction-stripping sequence also makes it possible to co-extract battery metals from a recycled battery leachate in one continuous recycling procedure using a single solvent to produce one or more battery-grade streams for direct synthesis of cathode material. If desired, depleted solvent collected after stripping can be recycled for reuse in the upstream liquid-liquid extraction stage, enhancing process efficiency. The method can be advantageously applied to any black mass leachate derived from recycling of spent batteries. As such, the method is effective to recover battery metals from a variety of spent batteries, including lithium-ion batteries. In that regard, the composition of streams resulting from the stripping stage can be advantageously tailored to be used in the direct manufacture of new cathode materials for lithium-ion batteries. Since the proposed procedure can rely on the use of a single solvent and straightforward pH tuning of the stripping aqueous solutions, the proposed process is significantly cost-efficient and versatile for recycling a varieties of battery, including conventional lithium-ion batteries. As such, the method presents as a significant step toward closing the loop on the life cycle of battery metals, such as lithium. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will be now described with reference to the following non- limiting drawings, in which: Figure 1 shows a comparison model data fitted with experimental data for equilibrium composition of impurities in the liquid-liquid extraction procedure described in in Example 1, Figure 2 shows the calculated extraction profile of extracting metals at varying pH, constant temperature of 21ºC, using a solvent comprising 16% Cyanex 272 and 10% TBP, from a synthetic black mass leachate relative to the liquid-liquid extraction procedure described in Example 1, Figure 3 shows a diagram of the three-stage counter-current liquid-liquid extraction unit described in Example 2, Figure 4 shows the McCabe-Thiele diagram for lithium in the cascade liquid-liquid extraction described in Example 2, Figure 5 shows a schematic of the recycling procedure for spent batteries described in Example 3, and Figure 6 shows a schematic of an integrated recycling process flow incorporating an embodiment method according to the present invention. The schematic shows integration of an embodiment method of the invention in a complete recycling loop, from the initial acid leaching of battery black-mass to the direct production of cathode material using metal extracted from the battery black-mass leachate. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of producing a battery-grade precursor solution. The expression "battery-grade" is used herein to indicate a composition including one or more battery metal(s) having a level of impurities below 1% by weight. As such, by being "battery-grade" said precursor solution would be of such quality as to be acceptable for use in a typical downstream battery refining plant, such as a precursor cathode active materials manufacturing plant. The exact specifications of said solution may vary depending on the intended use and the specifications of the manufactured cathode materials. In some embodiments, the battery-grade precursor solution is suitable for direct production of a cathode material. Those instances are particularly advantageous when the solution contains two or more battery metals. In those cases, the battery-grade precursor solution contains battery metals in a stoichiometric ratio characteristic of an intended cathode material. For example, a battery-grade precursor solution containing nickel, manganese and cobalt according to a 5-3-2 molar ratio can be used as is for the direct production of NMC532 cathode material, which has the same relative metal stoichiometry as the precursor solution. In some embodiments, two or more battery-grade precursor solutions collected from the stripping unit(s) have a composition such that they can be combined pro rata to obtain a solution containing battery metals in stoichiometric ratio corresponding to that of an intended cathode material. The method of the invention comprises a step of providing a battery black-mass liquid leachate. In a typical battery recycling procedure, spent batteries are collected, sorted, discharged and disassembled. This is followed by mechanical crushing, drying, sorting sieving and/or pyrolysis to remove any remaining electrolyte and potentially hazardous to health fluorine- containing components. The resulting fine material, physically separated from copper, aluminium, and polymer scrap materials, is what is referred to in the battery recycling industry as "black-mass". Accordingly, the expression "black-mass" used herein will be understood in accordance to its broadest meaning to mean a composition, typically in solid form, comprising at least one battery metal recovered from battery or battery-related input scrap feeds. For example, the black-mass may comprise at least one of lithium, cobalt, nickel, iron, and manganese. Typically, when a spent lithium-ion battery is recycled, the black-mass would comprise at least lithium. The battery black-mass may be obtained from a variety of sources, including spent batteries and scrap materials containing battery metals. These sources may include lithium-ion batteries, lithium metal batteries, solid state batteries, nickel-cadmium batteries, nickel- metal-hydride batteries, or other types of batteries. Different battery chemistries such as primary batteries and Ni-MH batteries may also be processed to produce black-mass. The actual composition of black-mass changes with the composition of the recycled battery. For instance, the composition of black-mass derived from a lithium-ion battery can vary significantly depending on the composition of the cathode as well as the producer. Also, several types of spent batteries may be recycled at the same time, resulting in a black-mass formulation resulting from the combined composition of those batteries. Black-mass suitable for use in the method of the present invention would therefore comprise at least one battery metal. With "battery metal" is meant herein a metal from the s-block (e.g. lithium) or d-block (e.g. cobalt, nickel, iron, and/or manganese) of the Periodic Table of Elements which is used for the manufacture of an active component of a battery. In some embodiments, the black-mass comprises at least one battery metal selected from lithium, cobalt, manganese, iron, and nickel. The black-mass may have any formulation deriving from the physical processing of one or more types of spent batteries. As a skilled person would appreciate, the composition of black-mass can be significantly diversified as the composition of batteries varies significantly across different producers, as well as from one application to another. Typically, black-mass derived from recycling of spent lithium-ion batteries includes at least a combination of cathode and/or anode electrode powders comprising lithium transition metal oxides and lithium iron phosphate (cathode) and graphite (anode). Materials present in rechargeable lithium-ion batteries also include organics such as alkyl carbonates (e.g. C₁- C₆ alkyl carbonates, such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), and mixtures thereof), iron, aluminium, copper, plastics, graphite, cobalt, nickel, manganese, and of course lithium. Typically, black-mass derived from spent lithium-ion batteries may contain up to 15 wt.% lithium, up to 60 wt.% cobalt, up to 70 wt.% manganese, up to 40 wt.% iron, and/or up to 60 wt.% nickel. The composition of black-mass differs significantly due to different battery providers, and chemicals of lithium-ion battery cathodes. The black-mass may also contain one or more impurities, which typically include battery elements other than battery metals, such as aluminium, phosphorous, and/or copper. For instance, a lithium-ion battery may contain up to 17% copper and up to 10% aluminium. Aluminium and copper impurities usually derive from the processing of the electron collectors of the battery, and phosphorous from remaining or decomposed electrolyte. Accordingly, in some embodiments the black-mass further comprises impurities selected from one or more of aluminium, phosphorous, and copper. In some embodiments, the black-mass derives from the processing of LFP batteries. In those instances, battery materials, including battery metals, present in the black mass may be expected to include a majority of phosphorous and iron (by weight) along with lithium. In the present invention, materials of the black-mass are provided in the form of a black- mass liquid leachate. As a skilled person would know, black-mass can be leached with a suitable leaching agent, typically an acid, a base, or supercritical CO₂. For instance, black mass leachate for use in the invention may be obtained by solid-liquid extraction of black- mass where the solid material (black-mass) is dissolved using a leaching agent. Said leaching agent can be either an inorganic acid such as H₂SO₄, HCl and HNO₃, or an organic acid such as citric acid, DL-malic acid and oxalic acid. If needed, leaching efficiency can be increased by adding a reducing agents (e.g. H₂O₂, glucose and/or NaHSO₃) to reduces the oxidation number of metal ions by donating electrons (e.g. Co³⁺, Mn⁴⁺ to Co²⁺, Mn²⁺, etc.). The leaching agent dissolves battery metals and other materials present in the black-mass, resulting in a liquid composition containing a mixture of the battery metals. Said composition may also include other battery materials and/or impurities of the kind described herein. Battery metals, such as lithium, cobalt, nickel, iron, and/or manganese, are typically present in the black-mass liquid leachate in the form of metal ions. The leaching agent is typically an aqueous acid or basic solution. Accordingly, in some embodiments the black-mass liquid leachate used in the method of the invention is an aqueous solution. The leachate may have a composition corresponding to that of the initial black-mass. In some embodiments, the black-mass liquid leachate comprises lithium, for example at least 5 mmol/L of lithium. In some embodiments, the black-mass liquid leachate comprises one or more of nickel, manganese, and cobalt. For example, the black-mass liquid leachate may contain one or more of nickel, manganese, and cobalt providing for a sum of their respective concentration of at least 35 mg/L. In some embodiments, the black-mass liquid leachate comprises one or more of iron, copper, and aluminium. The sum of the concentrations of each of iron, copper, and/or aluminium may be at least 20 mg/L. The method of the invention comprises a step of adding an immiscible liquid solvent to the liquid black-mass leachate. By being a "solvent", the immiscible liquid solvent used in the method of the invention is a liquid capable to solubilise the at least one or more battery metals. The liquid solvent used in the invention is an "immiscible" liquid solvent in that, under the process conditions described herein, it resists formation of a homogeneous liquid phase with the black-mass leachate, such that the solvent and the leachate remain separate from one another by a distinct liquid-liquid interface. For instance, when the black-mass leachate is an aqueous solution, the immiscible liquid solvent may be an organic liquid solvent. Any solvent that can dissolve the one or more battery metals while being immiscible with the black-mass leachate may be used in the method of the invention. In that context, when choosing an immiscible liquid solvent for use in the method of the invention a skilled person may have regard to a number of factors, for example the specific composition of the black- mass leachate and the solubility of the one or more battery metal in the solvent. Typically, the liquid immiscible solvent comprises a chelating agent (herein referred to also as "extractant") capable to coordinate metal ions in solution. Said chelating agent would be understood to be a chemical compound that can form complexes with the metal ions. Preferably, said chelating agent would have a high affinity for the target metal ions, and would be able to selectively extract them from the black-mass liquid leachate even in the presence of other species. The extractant may be a neutral or charged molecule, and may contain one or more donor atoms, such as nitrogen, oxygen, phosphorous, or sulphur, that can coordinate with the battery metal ions. The extractant may also contain one or more ligand groups, such as amine, carboxylic acid, or thiol groups, that can donate or accept electrons from the metal ions. Examples of suitable extractants for use in the invention include acid extractants, neutral extractants, or a mixture thereof. Any such extractant may be an organic extractant. For instance, the liquid immiscible solvent may comprise an organic acid extractants, an organic neutral extractants, or a mixture thereof. Suitable organic acid extractants may be selected from one or more of an organic acid extractant, chelating extractant, solvating extractant, and an organic basic extractant. Suitable organic acid extractants for use in the invention may include di-2-ethylhexyl phosphoric acid (D2EHPA), 2-ethylhexyl Phosphate (P507), mono-2-ethylhexyl (2- ethylhexyl) phosphonate (PC-88A), sulfanyl-sulfanylidene-bis[(2R)-2,4,4-trimethylpentyl]- lambda5-phosphane (Cyanex 301), bis(2-ethylhexyl) hydrogen phosphate (Ionquest 220), bis(2,4,4- trimethylpentyl)phosphinic acid (Ionquest 290, Cyanex 272) and/or a mixture thereof. Suitable chelating extractants for use in the invention may include β-hydroxyaryloximes (LIX84, Acoraga), β-diketone (Metral, EOL, HTTA, HBTA, LIX54), and/or a mixture thereof. Suitable solvating extractants for use in the invention may include phosphorus esters (TBP, TOPO), phosphine oxides (Cyanex 923), and/or a mixture thereof. Suitable organic basic extractants for use in the invention may include amines (Alamine 336, TOA, Aliquat 336), and/or a mixture thereof. Accordingly, in some embodiments the liquid immiscible solvent comprises di-2-ethylhexyl phosphoric acid (D2EHPA), 2-Ethylhexyl phosphonic acid mono-2-ethylhexylester (PC- 88A), bis-2,4,4-trimethylpentyl dithiophosphinic acid (Cyanex 301), bis(2,4,4- trimethylpentyl) phosphinic acid (Cyanex 272), neodecanoic acid (Versatic acid 10), LIX 84, or a mixture thereof. Organic extractants of the kind described herein are particularly suited for use when the black-mass leachate is in aqueous form. It will therefore be understood that in those circumstances the organic solvent would be immiscible in water. The liquid immiscible solvent may also comprise one or more modifiers to aid the extraction of the one or more battery metals from the black-mass liquid leachate. Suitable examples of said modifiers include trialkylphosphine oxide (TOPO), trioctylamine (TOA), tributyl phosphate (TBP), or Cyanex 923. Said additives can advantageously tune the selectivity of the solvent to the target metals. TOA and TBP may also act to improve poor phase behaviour during the liquid-liquid extraction by preventing third phase formation. The modifier may be used in an amount that is conducive to provide the required function. In some embodiments, the immiscible liquid solvent comprises a modifier in an amount from about 5 vol.% to about 20 vol.%. The extractant agent may be used pure as the immiscible liquid solvent, or diluted in a liquid diluent. Suitable diluents in that regard include kerosene or kerosene-based diluents (e.g. Vivasol 2046). The diluent may be used in an amount that is conducive to provide the required function. In some embodiments, the immiscible liquid solvent comprises a diluent in an amount from about 50 vol.% to about 90 vol.%. For instance, the immiscible liquid solvent may comprise a diluent in an amount from about 60 vol.% to about 80 vol.%. In some embodiments, the liquid immiscible solvent comprises Cyanex 272 and TBP. In some embodiments, the liquid immiscible solvent comprises Cyanex 272, TBP, and Vivasol 2046. Examples of suitable compositions of immiscible liquid solvents for use in the invention are listed in the Table below. Table 1 - Compositions of organic solvent used and their abbreviations Cyanex272 [v%] ^TBP Vivasol 2046 %

Adding the immiscible liquid solvent to said black-mass liquid leachate in the method of the invention will result in a biphasic liquid made of the immiscible liquid solvent and the black- mass liquid leachate separated by a liquid-liquid interphase (as in an oil and water mixture). The method of the invention requires adding the immiscible liquid solvent to the black-mass liquid leachate, and performing liquid-liquid extraction to load said liquid solvent with the one or more battery metals. Accordingly, and for avoidance of doubt, the expression "liquid- liquid extraction" is used herein to indicate a process by which the battery metals are transferred from the leachate liquid solution into the immiscible liquid solvent. The liquid-liquid extraction is intended to promote transfer of the one or more battery metal from the black-mass liquid leachate into the immiscible liquid solvent through the liquid- liquid interphase. For avoidance of doubt, it will be understood that during liquid-liquid extraction all types of battery metals contained in the black-mass liquid leachate will be loaded into the immiscible liquid solvent for subsequent separation in the stripping step. For instance, if the black-mass liquid leachate contains lithium, cobalt and manganese, all of those metals will be loaded into the immiscible liquid solvent during the liquid-liquid extraction for subsequent separation in the stripping step. For instance, when the black-mass leachate contains lithium (either alone or together with any other battery metal of the kind described herein), the method of the invention comprises performing liquid-liquid extraction to load the liquid solvent with said lithium (and the other battery metals, if any) contained in the black-mass liquid leachate. Accordingly, the present invention may also be said to relate to a method of producing a battery-grade precursor solution for production of a cathode material, the method comprising the steps of: providing a battery black-mass liquid leachate, said liquid leachate comprising one or more battery metals; adding an immiscible liquid solvent to said liquid leachate and performing liquid-liquid extraction to load said liquid solvent with all the one or more battery metals; and subjecting the resulting loaded liquid solvent to stripping in at least one stripping unit; wherein stripping is performed using an aqueous stripping solution having a pH that extracts the one or more battery metals into the aqueous stripping solution to provide for said battery-grade precursor solution. In other words, the present invention may also be said to relate to a method of producing a battery-grade precursor solution for production of a cathode material, the method comprising the steps of: providing a battery black-mass liquid leachate, said liquid leachate comprising one or more battery metals; adding only one immiscible liquid solvent to said liquid leachate and performing liquid-liquid extraction to load said liquid solvent with all the one or more battery metals; and subjecting the resulting loaded liquid solvent to stripping in at least one stripping unit; wherein stripping is performed using an aqueous stripping solution having a pH that extracts the one or more battery metals into the aqueous stripping solution to provide for said battery-grade precursor solution. Transferring all battery metals into the solvent phase in the liquid-liquid extraction step is particularly advantageous over conventional recovery systems, for example when recycling lithium-ion batteries. Lithium-ions can have poorer affinity towards extractant agents relative to the other battery metals. As a result, in conventional recycling procedures battery metals other than lithium (e.g. nickel, cobalt, and/or manganese) are extracted from the leachate phase while most of the lithium is retained in the leachate raffinate. In those instances, lithium is subsequently separated from the leachate raffinate with additional (and less efficient) separation procedures, such as chemical precipitation (e.g. as Li2CO3) or ion exchange (as LiOH). Advantageously, the present invention affords extraction and recovery of all battery metals in one continuous step using one solvent, with no need for additional targeted treatment of the extraction raffinate. In that regard, the operative conditions for the liquid-liquid extraction may be such that at least 50% (molar) of each of the one or more battery metal present in the initial black-mass liquid leachate is loaded into the immiscible liquid solvent. In some embodiments, the liquid- liquid extraction results in at least about 75% (molar) at least about 90% (molar), at least about 95% (molar), at least about 97% (molar), at least about 98% (molar) or at least about 99% (molar) of each of the one or more battery metal present in the initial black-mass liquid leachate being loaded into the immiscible liquid solvent. In some embodiments, the operative conditions for the liquid-liquid extraction may be such that at least 50% (molar) of lithium present in the initial black-mass liquid leachate is loaded into the immiscible liquid solvent. In some embodiments, the liquid-liquid extraction results in at least about 75% (molar) at least about 90% (molar), at least about 95% (molar), at least about 97% (molar), at least about 98% (molar) or at least about 99% (molar) of lithium present in the initial black-mass liquid leachate being loaded into the immiscible liquid solvent. In some embodiments, the loaded immiscible liquid solvent following liquid-liquid extraction contains lithium in a concentration of at least 70 mg/L. In some embodiments, raffinate exiting the liquid-liquid extraction step (i.e. the leachate phase depleted of the battery metals) comprises lithium in an amount of not higher than 140 mg/L. When the black-mass liquid leachate is an aqueous mixture, the pH of said leachate may be modulated to affect solvent loading (all other operative parameters being constant). Modulating the pH can assists with deprotonating the extractant agent such that it can effectively coordinate the metal ions. Typically, the pH of the leachate is maintained below 8.5 to avoid emulsion formation. Battery metals display significant extraction efficiency change at increasing pH. The changing range differs from different metals, which typically enables selective separation by adjusting the pH of the leachate phase. For a given formulation of the leachate and solvent, slope analysis can be useful to determine effective pH conditions within which to operate the liquid-liquid extraction. For a given composition of the liquid leachate, empirical equilibrium modelling can provide guidance on devising extraction parameters based on equilibrium compositions of the leachate and solvent phases. Equilibrium conditions may be expressed by the following formula (I): logC = logD_M – a· log [NaL_(org)] (I) in which logC is the extraction constant for a given metal M, and is representative of equilibrium constants and activity coefficients of metal ions in the leachate and organic phases, DM is the distribution ratio of metal M, a is the stoichiometric ratio of extractant molecular over metal ion, and [NaL_(org)] is molarity of deprotonated extractant agent in the solvent. Extraction data taken at different operating conditions (e.g. constant T and varying pH) provide values for D_M and NaL_(org) (assuming NaOH is used to as pH modifier), can be used to regress logC and a. The resulting data allow construction of slope concentration curves for each metal at varying pH, for a given extraction temperature. A representative empirical procedure to determine equilibrium data for a given leachate composition and solvent composition is provided in Example 1. In some embodiments, the liquid-liquid extraction is performed at a pH of from about 2.0 to about 9.0. In some embodiments, the liquid-liquid extraction is performed at a pH of at least 5.5, for example from 5.5 to about 8. The proposed pH range was found to be particularly effective to achieve the intended extraction of the one or more battery metals using the same solvent. For example, it was advantageously found that performing extraction using pH above 5.5 can be particularly useful to perform combined extraction of lithium with all other battery metals, for example when lithium displays less affinity to the extractant agent than the other battery metals. In some embodiments, the pH of the leachate liquid phase during liquid-liquid extraction is at least about 6, at least about 7, or about 8. Any pH modifier can be used to modulate the pH of the leachate phase to the desired values. Suitable examples of pH modifiers for use in the method of the invention include NaOH, lime, and/or ammonia solution. Provided the liquid-liquid extraction results in the transfer of said one or more battery metals into the immiscible liquid solvent, the extraction can be effected by any means and under any conditions known to the skilled person. The liquid-liquid extraction in the method of the invention may involve contacting the black- mass liquid leachate and the immiscible liquid solvent in a separation vessel, such as a mixer- settler, an extraction column, or a centrifugal contactor. The leachate and organic phase are mixed together, allowing the extractant forming the solvent to complex with the metal ions of the leachate at the liquid-liquid interface. The mixture is then allowed to separate into two phases, with the metal ions and extractant being preferentially solubilized in the solvent phase to provide a loaded solvent, and the remaining species being present in the raffinate. Those skilled in the art would be aware of a number of operation conditions that can be tuned to effect the required extraction. In that context, a skilled person would recognise that extraction conditions such as, initial leachate pH, initial leachate oxidation potential, equilibrium pH, extractant concentration, relative volume ratio of immiscible liquid solvent / liquid leachate volume ratio (also referred to as "organic/aqueous", or "O/A ratio" when the solvent is an organic solvent and the leachate is in aqueous form), temperature, time, and extraction system (extractant concentration, and/or leachate composition), can interplay to affect extraction efficiency. In some embodiments, the liquid-liquid extraction is performed with a volume ratio of immiscible liquid solvent / liquid leachate volume ratio (also referred to as "organic/aqueous", or "O/A ratio" when the solvent is an organic solvent and the leachate is in aqueous form) of between 0.1 and 10, for example 6. The liquid-liquid extraction may be performed at any temperature conducive to achieve the intended extraction. In some embodiments, the liquid-liquid extraction is performed at a temperature from about 10°C to about 85°C, for example 21°C. The extraction units for the liquid-liquid extraction may be arranged in a variety of configurations known to the skilled person, provided the extraction results in the immiscible liquid solvent being loaded with the one or more battery metals. For instance, the extraction units may be configures in series or parallel, or a combination thereof. In a series configuration, the leachate is passed through each extraction unit in sequence, with the raffinate from one unit serving as the feed for the next unit. In a parallel configuration, the leachate is divided and passed through multiple extraction units simultaneously. In some embodiments, the liquid-liquid extraction is performed in a series of two or more extraction units operating in counter-current. In some embodiments, the liquid-liquid extraction is performed in a series of three extraction units operating in counter-current. Advantageously, when the leachate contains lithium, performing the liquid-liquid extraction in a cascade of multiple units can assist with the mass transfer of lithium, improving its transfer into the immiscible solvent, for example where affinity of lithium to the extractant agent is poorer than that of the other battery metals. An example of one such arrangement is shown in Figure 3. Slope analysis and McCade-Thiele diagrams can assist the skilled person in devising adequate operative conditions to achieve extraction of the one or more battery metals when operating with multiple extraction units. For instance, for a given pH one may consider modulating the immiscible liquid solvent / liquid leachate volume ratio (also referred to as "organic/aqueous", or "O/A ratio" when the solvent is an organic solvent and the leachate is in aqueous form) to prevent undesired precipitation of immiscible salts. This may be an issue at high pH (e.g. pH of up to 8), at which metals such as manages, cobalt, nickel, aluminium, and/or copper may precipitate as the metal hydrolyses. For a given pH, one may determine the maximum tolerating concertation of a given metal based on the corresponding solubility product constant characteristic of the hydrolysis equilibrium reaction, then consider the adequate operating immiscible liquid solvent / liquid leachate volume ratio (or the O/A ratio in case of organic solvent / aqueous leachate system) to ensure the metal does not exceed said maximum tolerating concertation during extraction. A reference procedure in that regard is described in Example 2. In some embodiments, the method of the invention further comprises a filtration step upstream of the liquid-liquid extraction step. The filtration step may be recommended in case the liquid leachate contains metals (such as iron) having extremely high affinity to the extractant agent. In those instances, presence of those metals may compromise the extraction efficiency in the downstream steps, making it preferable to extract them prior to the liquid- liquid extraction stage. Filtration may be achieved by any means and procedures effective to selectively separate the target impurity metal from the leachate stream. For instance, the target impurity metal may be first precipitated by chemical means, and the precipitate subsequently mechanically filtered out of the leachate stream (e.g. by way of a plate and frame filter). In some embodiments, the filtration step is intended to separate iron from the black-mass liquid leachate upstream of the liquid-liquid extraction step. In those instances, iron may be chemically precipitated (for example as ferric hydroid) and filtered (for example by a plate and frame filter). An example in that regard is provided by the inline precipitation/filtration units G2 and G3 in the process schematic of Figure 5. The method of the invention comprises a step of subjecting the resulting loaded liquid solvent to stripping in at least one stripping unit. A main purpose of the stripping step is to selectively extract one or more battery metals from the loaded immiscible liquid solvent into one or more battery-grade solution streams, in which battery metals are contained in an amount, purity, and/or relative ratio suitable for use of said streams as battery-grace precursor solutions for cathode materials. Stripping of the target battery metals is achieved by contacting the loaded solvent with an aqueous stripping solution. Accordingly, and for avoidance of doubt, the term "stripping" is used herein to indicate a process by which the battery metals are transferred from the immiscible liquid solvent into a stripping solution, in this instance an aqueous stripping solution. In the method of the invention, said aqueous stripping solution has a pH that extracts the one or more battery metals into the aqueous stripping solution to provide for said battery-grade precursor solution. Accordingly, the initial pH, the initial composition, and the relative volume of the stripping solution can be controlled such that, as stripping progresses in the stripping unit, the pH of the stripping solution reaches an equilibrium value at which the composition of the target metal(s) in the solution corresponds to the desired battery-grade formulation. As a result, the battery metal(s)-enriched aqueous stripping solution exits the stripping unit at the equilibrium pH characteristic of a targeted stoichiometric ratio of metal(s). In some embodiments, said aqueous stripping solution has a pH that extracts the one or more battery metals into the aqueous stripping solution to provide for a battery-grade precursor solution having a stoichiometric ratio of metal(s) making it suitable for direct production of a cathode material. That is, said battery-grade solution can be used for direct production of cathode material with no need for additional preparation (for example addition of other metal precursors such as CoSO₄, NiSO₄, LiOH, Li₂CO₃, etc.). Those instances are particularly advantageous when the solution contains two or more battery metals. In those cases, the battery-grade precursor solution contains battery metals in a stoichiometric ratio characteristic of an intended cathode material. For example, a battery-grade precursor solution containing nickel, manganese and cobalt according to a 5-3-2 molar ratio can be used as is for the direct production of NMC532 cathode material, which has the same relative metal stoichiometry as the precursor solution. The equilibrium pH of the stripping solution affects the solubility and stability of the target battery metal(s) species present in the loaded solvent. During stripping, transfer of the target battery metal(s) from the loaded solvent into the stripping solution is controlled by the state of the extractant in the loaded solvent. Accordingly, depending on the solubility of the target battery metal(s) at different pH values in a given solvent and a given aqueous leachate, adjusting the pH of the stripping solution makes it possible to selectively extract or reject certain battery metals, and reject certain impurities according to the desired battery-grade composition one intends to achieve in the stripping solution. The pH of the stripping solution may be any pH leading to the transfer of the desired type and amount of battery metal(s) from the solvent to the aqueous solution. A skilled person practicing the invention will understand that in that context, the selection of the appropriate initial and equilibrium pH values of the stripping solution depend also on the nature of the extractant in the solvent. In that regard, slope analysis, or pH dependence of metal extraction for a given solvent can assist to devise the appropriate pH of the stripping solution when targeting specific equilibrium composition of metals. In some embodiments, the stripping solution has an initial pH of from -2 to 8. For example, the stripping solution may have a pH of from -2 to 7, from -2 to 4, from -2 to 3, from -1 to 3, from -0.5 to 3, from -0.5 to 1, from -0.25 to 0.6, from -0.15 to 0.54. In some embodiments, the stripping solution has an initial pH of -0.15, 0.35, or 0.54. Advantageously, for a given solvent, pH modulation of the stripping solution(s) can be automated based on the composition of the loaded solvent and that of the target battery-grade stream. This may be achieved, for example, by continuously monitoring the pH of the stripping stream(s), and adjusting it to optimize the separation and enrichment of the target components. During stripping, the target equilibrium pH of the aqueous phase is reached dynamically as battery metals transfer from the solvent into the stripping solution. Any aqueous stripping solutions may be used in that regard, provided the pH of the solution can be modulated. In that regard, pH modulation may be performed using any suitable acid or base. The specific acid or base used will depend on the solubility of the battery metals in the stripping solution at different pH values. In some embodiments, said aqueous stripping solution is an aqueous solution containing an acid selected from HCl, H₂SO₄, HNO₃, citric acid, lactic acid, malic acid, oxalic acid, and a mixture thereof. Provided stripping achieves transfer of the target metals from the loaded solvent into the stripping solution, stripping may be performed by any means known to the skilled person. For instant, stripping may be achieved by promoting intimate contact between the loaded solvent and water in a mixer-settler, for example a cascade of mixer settlers through which the liquid phases flow in co-current, cross-current, or counter-current arrangement. In some embodiments, stripping is performed in a cascade of two or more units in series, for example three units in series. An example in that regard is represented by units B, C, and D in the schematic of Figure 5. Parameters such as residence time (i.e. contact time) of the loaded solvent and the stripping solution in the striping unit(s) may be controlled to ensure the desired equilibrium pH is reached. Accordingly, for a given stripping unit, residence time of the contacting solvent and stripping solution can be adjusted to any value conducive to produce an aqueous stream having a required battery-grade composition. In some embodiments, stripping is performed using a residence time of at least about 30 seconds, at least about 60 seconds, at least about 120 seconds, at least about 180 seconds, at least about 240 seconds, at least about 300 seconds. When the stripping step is performed in a cascade of multiple stripping unit in series, the total amount of residence time may be at least about 10 minutes, at least about 20 minutes, at least about 30 minutes, or at least about 60 minutes. Stripping may be performed at any stripping temperature conducive to produce an aqueous stream having a required battery-grade composition. For instance, the stripping temperature may be at least about 15°C, at least about 20°C, at least about 25°C. In some embodiments, the stripping temperature is from about 15°C to about 25°C. For example, the stripping temperature is about 21°C. In a general sense, higher stripping temperatures can be beneficial to reaching equilibrium conditions. When stripping is conducted in a cascade of multiple stripping units, the pH of the stripping solution used in one or more of those units can be independently modulated to target specific formulations of the aqueous phase exiting a given unit, for example to obtain a battery-grade solution. For example, stripping may be conducted in a cascade of stripping units, each unit operating at a different pH of the stripping solution to achieve streams with different compositions. Any of said streams may be a battery-grade solution having stoichiometry of metal(s) according to the requirement of battery cathode material compositions, or may be combined pro rata to obtain battery-grade solutions according to the requirement of battery cathode material compositions. An example practical implementation in that regard is presented in Example 3, with reference to the system schematic of Figure 5. In some embodiments, an enriched aqueous solution exiting the one or more stripping unit(s) comprises lithium in a concentration of at least 70 mgl/L, for example at least 350 mg/L. For example, said enriched aqueous solution may contain lithium in a concentration of at least about 350 mg/L and other battery metals in a concentration lower than about 1000 mg/L. In some embodiments, an enriched aqueous solution exiting the one or more stripping unit(s) comprises 0.1-0.5 mol/mol lithium, 0.1 – 0.5 mol/mol nickel, 0.01 – 0.5 mol/mol manganese, and 0.01 – 0.5 mol/mol cobalt. The solution can advantageously be directly collected from the aqueous phase of a stripping unit, with stoichiometric ratio of the metals aligned for direct production of cathode material, i.e. without the need for further preparation (e.g., adding other precursor chemicals, such as CoSO₄, NiSO₄, LiOH, Li₂CO₃, etc.) and/or precipitation. In some embodiments, stripping is performed in a cascade of three stripping units in series, each unit operating at an equilibrium pH of the stripping solution of 6, 4.5, and 3, respectively. An example of one such stripping procedure is described in detail in Example 3. In those instances, the first stripping unit may operate to produce an aqueous stream having a battery-grade formulation of about 95.8 mol % Li and about 4.2 mol % Nickel. Said battery-grade stream can be used for direct production of battery grade lithium cathode. The second stripping unit may operate to produce an aqueous stream having a battery-grade formulation of about 51.2 mol % Li, about 40.1 mol % Ni, about 1.95 mol % Mn, and about 6.54 mol % Co. Said battery-grade formulation would be suitable for the synthesis of a cathode for an LNMC811 battery. The third stripping unit may operate to produce an aqueous stream having a battery-grade formulation of about 2.8 mol % Li, about 5.2 mol % Ni, about 35 mol % Mn, and about 55.9 mol % Co. Battery-grade solutions collected downstream of one or more stripping used can be advantageously used as precursor solutions for production of a variety of cathode materials. Example of cathode materials in that regard include LCO, LFP, LMO/LMNO, NCA80, NCA90, NMC333, NMC532, NMC523, NMC622, and NMC811. The cathode material may be produced by any suitable method, including chemical synthesis (e.g., co-precipitation, solid state reaction, sol-gel synthesis), physical vapor deposition (e.g., spray pyrolysis), or electrodeposition (e.g., electrospinning). The choice of method will depend on the specific requirements and properties of the battery-grade precursor and the desired final product. Lean immiscible solvent collected downstream of the stripping step may contain residual impurities, for example residual aluminium and/or copper impurities, or residual metals such as iron. In those instances, the lean solvent may undergo washing for impurity removal. Said washing may be performed in accordance to any procedure known to the skilled person, for example further stripping. In some embodiments, washing comprises saponification of the lean solvent. This may be achieved by any means known to the skilled person. For example, saponification of the lean solvent may be performed by adding a base to the lean solvent. Examples of suitable bases in that regard include NaOH, ammonia, and/or lime. An example of a saponification unit in the context of an embodiment method is represented by unit F in the schematic of Figure 5. In those instances where solvent is recycled into the liquid-liquid extraction step, saponification downstream of the stripping step may be performed to regenerate the solvent to conditions appropriate for the liquid-liquid extraction. An example for the regeneration in the context of an embodiment method is represented by the mass flow from unit F to unit A1 in the schematic of Figure 5. Figure 5 shows an example schematic of a recycling process that incorporates the method of the invention. The process in the schematic of Figure 5 covers the upstream leaching of black-mass obtained from spent batteries. The black mass is introduced in a stirrer tank G1, where it is leached with HCl stream G101 (for example an aqueous solution of HCl) to produce black- mass liquid leachate (stream G102). Reverse osmosis (RO) unit H provides leaching unit G with RO water recycled from saponification unit F, which is located downstream of stripping units B-D. In a working example, 31.5% HCl and water treated from the reverse osmosis unit H can be mixed with the solid black-mass to achieve required leaching condition. Insoluble graphite is separated from soluble cathode and copper-aluminium scraps. Black-mass leachate aqueous solution G102 is then pumped into a second mixer G2, where excess acids are neutralised by adding alkali. Addition of alkali contributes to hydrolysis and precipitation of iron from the black-mass leachate solution, which can be filtered by a plate and frame filter (units G3 downstream of G103). Hydrolysis of other metals in the liquid leachate can be neglected at this stage. In the example scheme, NaOH is introduced (stream G302) into the stirrer tank that receives the black-mass leachate to induce formation and precipitation of iron hydroxide. The iron hydroxide is then transferred to a plate filter through stream G103, resulting in iron-depleted filtered stream G104 and Fe(OH)₃ filtrate G303. Filtrate G303 may be either disposed of, or the iron used for production of iron-based cathode materials (e.g. LFP), for example in combination with suitable streams collected from at least one of the stripping units. Black-mass aqueous leachate G104 stream is subsequently fed into liquid-liquid extraction cascade units A. In cascade units A, battery metals are efficiently extracted from the leachate phase and loaded into an immiscible liquid solvent. In the schematic of Figure 5, the immiscible liquid solvent is fed into the units as washed solvent stream F201, which is recycled from unit F downstream of stripping units B-D. Battery metals are sequentially loaded into the immiscible liquid solvent as it flows through cascade extraction units A (streams A201, A202, and A203). The leachate phase is progressively depleted of battery metals as it flows through cascade extraction units A (streams A101, A102, and A103), and is eventually discarded as raffinate stream A103, then circulated back to unit H to be treated. Loaded solvent stream A203 exits the liquid-liquid extraction units A and is fed into stripping unit B ,which is the first of three cascade stripping units B, C, and D. Individual aqueous stripping solutions are fed into each of units B-D as streams B101, C101, and D101, and sequentially strip battery metals out of the solvent. As fed, the stripping solutions are aqueous solutions of acid, which in schematic of Figure 5 is HCl. After each stripping stage, the solvent phase exits units B-D as stripped streams B201, C201, and D201. Solvent streams B201 and C201 are respectively fed into subsequent stripping units C and D. In a working procedure, equilibrium pH of aqueous streams B102, C102 and D102 exiting stripping cascade units B-D, respectively, may be tailored to provide battery-grade formulations (e.g., 6.00, 4.50, and 3.20 in Example 3). Those streams may each respectively comprise lithium, nickel and lithium, and cobalt and manganese. These streams can potentially be used as is, or combined to produce new lithium-ion battery cathode material. The schematic of Figure 5 also includes a further stripping unit E, in which solvent stream D201 exiting stripping unit D, or a portion of it (stream D203), can be stripped of further impurities (e.g. aluminium) or other metals (e.g. iron) at more acidic conditions with stream E101/102. Stripping with stream E101/102 is important to compensate the iron and aluminium accumulation through the process. The ratio of stream D202 and D203 can be typically assumed to be 1/9. Saponification unit F downstream of stripping units B-E treats the portion of solvent phase in stream D201/D202 exiting stripping unit D as well as the further stripped portion of solvent stream E201 exiting stripping unit E. Saponification is intended to deprotonate the lean solvent to level suitable for liquid-liquid extraction before the solvent is recycled into extraction units A as washed solvent stream F201. All mass transfer in liquid-liquid extraction units A, stripping units B-E, and saponification unit F can be practically achieved by any means known to the skilled person. For example, all units may be equipped with mixer-settlers. The mixer-settlers may be made of any suitable material, for example selected based on its corrosion-resistance to acids and process chloride. A suitable example in that regard is S31600 austenitic stainless steel, for example with 3 mm thickness. The total residence time in these mixer-settlers can be up to 40 minutes. Without wanting to me limited by theory, it was found the stripping may be chemical reaction controlled, requiring 30 minutes for all metals to be stripped from the organic phase. A working example the process scheme of Figure 5 is described in Example 3. The method of the invention can provide for recovery of over 95% of a target battery metal. For example, when recycling lithium batteries the method of the invention affords recovery of over 95% lithium. The recovered lithium can be used directly to manufacture next- generation batteries. The proposed method is also advantageously simple. With minimal steps and units, all critical materials can be recycled in sufficient amount for reuse for direct cathode manufacturing. The proposed method can also afford high level of integration with existing cathode manufacturing procedures, providing for efficient cathode resynthesis plants. An example of such integration is shown in the schematic of Figure 6. In the schematic, acid leaching of the battery black-mass is performed in the first process block using an aqueous solution of H₂SO₄. Following excess acid neutralisation with compressed gaseous NH₃ or liquid ammonia solution, the resulting leachate is fed to the liquid-liquid extraction section. In the extraction section, battery metals are extracted from the leachate phase and loaded into washed organic solvent recycled from downstream of the stripping block. The extraction column is intended to have more than 3 theoretical stages, for >90% lithium, > 99% Ni, Co, and Mn yield. Aqueous raffinate generated in the extraction block can be used to regenerate condensate water for use in the black-mass leaching, significantly minimising liquid waste. The schematic of Figure 6 shows relevant passages and operative conditions of the integrated synthesis plant numbered from (1) to (6), namely: (1) neutralisation of the excess acids; (2) use of more than three theoretical stages, for > 90% Li and > 99% Ni, Co, Mn yield; (3) minimisation of the liquid waste; (4) chelating organic acids (such as citric acid); (5) Sol- Gel cathode synthesis, alternatively, co-precipitation; (6) calcination at 450 C for 5 hours, then 900°C for 2 hours; (7) regeneration to remove Fe(III) and Al(III); (8) 90% neutralised. Loaded organic solvent exits the extraction block as pregnant leach solution (PLS), and is fed into the stripping section. In the schematic, stripping is performed in a cascade of three mixer-settler units using a chelating organic acid (e.g. citric acid) solution fed into each stripping units. Lean organic solvent is collected downstream of the stripping units and sent to a regeneration block, where it is washed for removal of residual Fe(III) and Al(III) impurities, 90% neutralised, and recirculated as washed organic solvent into the liquid-liquid extraction column. Battery-grade solutions of lithium, nickel, cobalt, and manganese are collected from the stripping units and transferred to the cathode synthesis section. The solutions of battery metals either possess already a target metal stoichiometry for direct production of cathode material, or can be mixed to obtain the desired metal stoichiometry for cathode fabrication. In this case, LMNC cathode material is produced using a sol-gel synthesis route, terminating with a two-stage oven calcination (450°C for 5 hours, then 900°C for 2 hours to produce the final cathode material). The proposed method is significantly flexible, affording production of battery-grade solutions irrespective of the nature of the starting spent battery. In that regard, pH modulation of the stripping unit(s) can effectively achieve production of solutions with formulation that is tailored to the target cathode material. The ability to recycle battery metals and “close the loop” on their life cycle will directly impact the need for virgin materials, while simultaneously reducing the carbon footprint required for new mining activities. As a result, the proposed method can provide an efficient pathway toward development of environmentally sustainable and economically viable recycling technologies, which are becoming a critical focus area as the global demand for battery manufacturing grows. Certain embodiments of the present invention will now be described with reference to the following non-limiting Examples. EXAMPLES EXAMPLE 1 Equilibrium data for the liquid-liquid extraction of battery metals was obtained using a synthetic back-mass leachate. Chemicals and leachate composition All chemicals used for the experimental section are listed in Table 2. All preparations were conducted at the room temperature of 21±1 ºC. Table 2 - Chemicals used Chemicals Vendor Batch number Min. Assay w% NiCl2•6H₂O Chem-Supply 316206 97

Table 3. The metallic valences are affected by the oxidation/reduction potential (Eh). These were validated according to Eh of approx. 1000 mV {#288}, and Geochemist Workbench. The synthetic solution was prepared by dissolving chemicals in RO (reverse osmosis) water without further purification. p f y y, P B T

Measure the equilibrium data at varying pH Each metal chloride salt was dissolved in 2 mol/L NaCl, to prepare for 0.01 mol/L chloride solution.50 mL of aqueous solution and 50 mL organic solvent were contacted in a jacketed cylinder at temperature of 21 ºC.10 mol/L, 1.0 mol/L, and 0.1 mol/L sodium hydroxide were used to gradually adjust the pH. The total volume of sodium hydroxide added was less than 2.5, with minimal impact to the aqueous volume. Preliminary tests showed 15 mins was plenty to achieve equilibrium. At each equilibrium, 0.250 mL aqueous phase was pipetted for analysis in ICP-OES (Inductively Coupled Plasma Atomic Emission Spectroscopy, Agilent ICP-720). The overall aqueous sampling volume was 3.5 mL. The organic solvent was took off to balance the volume. The extraction was controlled at pH lower than 3.5 for impurities. Isothermal equilibrium with different O/A The Isotherm experiment was conducted at 21ºC to examine ESI for the synthetic leachate. The solvent was prewashed (deprotonated) by 10 mol/L NaOH (88.47 mL per mol Cyanex 272). 40 mL aqueous solution was contacted with gradually added washed organic solvent (from 16.0 mL to 99.8 mL). pH values at various volumes were constant as 7.54 ± 0.02. At each condition, 0.250 mL aqueous phase was pipetted for analysis in ICP-OES. Equilibrium data Regressed Parameters for Impurities A mathematical model as described herein (see formula (I)) described the extraction performance. The results were used with Formula (I) with determined parameters a and logC . The values used are listed in Table 4. Table 4 - Parameter for metal extraction g with Cyanex 272, at 21ºC C_ation ^{^ ^^^ ^ Conc. range} For lithium

ted extractant is measured as 0.338 mol/L, logD_Li equals 0.1289 + 0.1289 × log(0.338) equals 0.0682. The concentration of lithium in the organic and aqueous phase can be calculated by skilled person by the distribution ratio (D_Li) and mass balance. Same principle applies for other ions. The concentrations of all metals in process streams can be calculated by skilled person, and validated by experiments by skilled person. Figure 2 shows the extraction profile of extracting metals at varying pH, constant temperature of 21ºC, initial concentration of 0.01 mol/L, using a solvent comprising 16% Cyanex 272 and 10% TBP, from 2 mol/L NaCl solution, produced by ESI. EXAMPLE 2

Equilibrium in a three-stage counter-current extraction unit

A three-stage counter-current scheme was selected for scaling up. Lean organic solvent and black-mass leachate enter the unit from different sides of the unit. The organic solvent, cascading from each stage, contacts higher aqueous concentration. The species loaded in the organic phase is higher, thus the recovery rate of metals can be improved.

A typical flow map of a three-stage counter-current unit is shown in Figure 3.

and are metallic molarity concertation in organic and aqueous phases, i denotes

the stage number where flows come from. The aqueous leachate is fed to the first stage, while the aqueous raffinate leaves the unit after the third stage. and denotes these two aqueous flows accordingly. Meanwhile and are concentrations for pregnant and lean solvent.

Lithium, as the key component, its isotherm data was used to represent the equilibrium on each stage graphically in Figure 4. The diagram composed of the operating line (slope = and the stepwise evolution is well-known as McCade-Thiele diagram. The 0 / A was

assumed as 6.0.

Traditionally, the McCabe-Thiele diagram is solved graphically with an operating line and an equilibrium line. However, it has also come to realisation that the isotherm is not a fixed curve. Nuanced aqueous composition can change isotherm equilibrium. In this study, the equilibrium of each stage depends on the aqueous composition entering each stage. Concentrations of each stage requires iterating metallic distribution ratios on each stage, which is a function of the organic and aqueous compositions. Thus, the equilibrium curve is not plotted in the diagram.

The data for Figure 4 is tabulated in The recovery rate of lithium after a three-stage counter-current unit is calculated as 98.6%. It proves the idea that lithium single stage extraction efficiency E% of approx.50% is plenty in a scaled-up solvent extraction process. Table 5 below, in addition to all other metals. The recovery rate of lithium after a three-stage counter-current unit is calculated as 98.6%. It proves the idea that lithium single stage extraction efficiency E% of approx.50% is plenty in a scaled-up solvent extraction process.

q f g Leachate Feed ^[^_^ ^{^} ^^{^} ^_^ ]_!^^^

EXAMPLE 3 Full recycling process A schematic of a full recycling plant performing the method of the invention is shown in Figure 5. The process scheme covers the upstream leaching, where all metallic oxidates are released into the acid solution. After pre-treatment, metals are extracted in one step by a solvent (e.g. comprising 16% Cyanex 272 and 10% TBP) in unit A. The Stripping is conducted in units B, C, and D at different pH values to achieve streams with different compositions. These streams are combined pro rata according to the requirement of battery cathode material compositions. Proportional lean solvent bleeds out to further strip impurities – aluminium – or other metals (e.g. iron) in unit E, at more acidic condition. Solvent is then washed (in a procedure also named "saponifying" industrially, or "deprotonation") in unit F prior to being recycled into unit A for contacting with leachate. Representative mass balance, flow information and specification will be described further below. The throughput of such recycling process is estimated to be 13.2 kg/hr black-mass, that is equivalent to 68.6 tonne of active cathode materials annually (about 300 operating days). That is also equivalent to approximately 680 electric vehicles batteries (estimated by an electric vehicle containing an average of 100 kg cathode active material). All key units in the system are labelled from A to H. Streams around the unit are numbers (e.g. A101). For reference, the first letter in the labels represents which unit the stream comes from. The first digit in the label represents the types of the stream, here 1, 2, and 3 stand for aqueous, organic and solid flow accordingly. Continuous mixer settler units may be selected as the most significant separation unit in the proposed schematic, as they are easier to design and require less data than other extraction unit (e.g. pulsed column). Mixer settlers are also used in hydrometallurgical and pharmaceutical processes. A mixer may be coupled with a settler, functioning as one single stage, allows the contact and settling of two liquid phases cascading, so that the equilibrium can be approached in each stage. In a mixer, liquid phases need sufficient agitation to be broke into small and dispersed drops, to enhance the mass transfer. Drops then coalesce and settle in the settler. Leaching and Pre-treatment Prior to the solvent extraction, leaching is an essential process in the first mixer G. In the mixer, 31.5% HCl and reverse osmosis (RO) water are sufficiently mixed with the solid black mass. Insoluble graphite can be separated at this stage from soluble cathode and copper-aluminium scraps. For reference, residence time in a 94.4 L leaching mixer is calculated as 900 second, being sufficient to achieve leaching efficiency of 99% or above. The leachate G102 is then pumped to the second mixer G, where excess acids are neutralised by addition of solid NaOH, neglecting the heat of dissolution. The leachate leaves the mixer at pH of 3. Precipitated ferric hydroxide is filtered by a plate and frame filter. In the meantime, hydrolysis of other metals can be neglected. The pre-treated leachate G104, having the same composition as the feed, enters a three-stage mixer settler pattern (units A), at temperature of 21 ºC, and pH of 3. In a real operation, the temperature can be higher than 21ºC, due to the residual heat from leaching and dissolving heat. In preliminary test, it was proved that higher temperature is beneficial to the equilibrium. However, the heat loss to the ambient temperature cannot be calculated without pilot trails. The rest of operations were assumed to be operated at 21ºC. All mixers G can be made of S31600 austenitic stainless steel (abbreviated as 316), with thickness of 3 mm. The material is selected for its corrosion-resistance to acids and chloride. Details about the equipment and the flows are listed from Table 6 to Table 8 below. q p g f g p G^{1 Mixer-1 G2 Mixer-2 G3} P_{late and Frame Filter}

Liquid-liquid extraction Liquid-liquid extraction was conducted in mixer-settlers A1 to A3 at temperature of 21 ºC. Equilibrium data was previously described in Table 4. The flowrate of the aqueous is 377 L/hr, the flowrate of the solvent is 2262 L/hr, and therefore the organic phase over aqueous phase ratio (O/A) is 6.0. The resident time is 40 seconds in each mixer, and 240 seconds in each settler. The total residence time of 270 seconds in each stage was assumed to be sufficient to reach equilibrium. This was proved by the trials in the lab bench scale and kinetic studies of other researchers with similar extraction system. Operational parameters and composition of the organic and aqueous phases in the extraction units is presented from Table 9 to Table 11. Table 9 - Equipment design table for liquid-liquid extraction units A A1 A2 A3 T ^º

(q p ) f q q Stream ID A101 A102 A103 N Rffint

Stripping The extracted solvent is then stripped at mixer-settlers B, C, D, and E, at different pH values. The total residence time in these mixer-settlers is 40 minutes. Stripping kinetics were not fully studies in this study. In preliminary study, it was found the stripping is chemical reaction controlled, which requires 30 minutes for all metals to be stripped from the organic phase. Details of all four stripping are listed from Table 12 to Table 14. Equilibrium pH of stripping cascades was 6.00, 4.50, and 3.20 for aqueous streams of B102, C102 and D102, respectively. These three streams are made of mostly lithium (B102), nickel and lithium (C102), or cobalt and manganese (D102). These streams can then be combined to synthesis new lithium-ion battery cathode materials, if needed. Stream B102 is an aqueous sodium chloride solution composed of 95.8 mol % lithium, 4.2 mol % nickel, with impurity less than 0.05 mol %. The stream is a battery-grade solution for direct use as a compensation for the production of battery grade lithium. Stream C102 contains 51.2 mol % lithium, 40.1 mol % nickel, 1.95 mol % manganese and 6.54 mol % cobalt. This ratio makes the stream suitable for direct synthesis of, for example, LNMC811 cathode. Stripping at -0.5 with stream E102 is important to compensate the iron and aluminium accumulation through the process. The bleeding ratio of stream D202 and D203 are assumed to be 1/9. Table 12 - Equipment design table of stripping B C D E

(q ) f pp g Stream ID B101 B102 C101 C102 D101 D102 E101 E102 Name

Washing Lean solvents stripped at pH of -0.5 and 3.2 are combined before entering mixer-settler F. These solvents are mixed with 4.05 mol/L NaOH, for 253 seconds. This allows efficient saponification prior to the contact with leachate, achieving equilibrium pH of each stage as 8.0. Detailed design specifications are summarised from Table 15 to Table 17. Table 15 - Equipment design table of washing F

( g ) f g Stream ID F201 F202 N m W S l

eficiation prior to leaching, the content of iron from steel packs can be minimised. However, iron may also be introduced from LFP cathode. In those instances, iron will be inevitable mixed in the black mass, which cannot be separated mechanically. Due to the extreme high affinity of Cyanex 272 and Fe³⁺. Extra upfront precipitation and bleeding stripping afterwards are required for solvent. As used herein, the term “about”, in the context of numerical values, typically means +/−5% of the stated value, more typically +/−4% of the stated value, more typically +/−3% of the stated value, more typically, +/−2% of the stated value, even more typically +/−1% of the stated value, and even more typically +/−0.5% of the stated value. Throughout this specification and the claims which follow, unless the context requires otherwise, the word ‘comprise’, and variations such as ‘comprises’ and ‘comprising’, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A method of producing a battery-grade precursor solution for production of a cathode material, the method comprising the steps of: providing a battery black-mass liquid leachate, said liquid leachate comprising one or more battery metals; adding an immiscible liquid solvent to said liquid leachate and performing liquid- liquid extraction to load said liquid solvent with the one or more battery metals; and subjecting the resulting loaded liquid solvent to stripping in at least one stripping unit; wherein stripping is performed using an aqueous stripping solution having a pH that extracts the one or more battery metals into the aqueous stripping solution to provide for said battery-grade precursor solution.

2. The method of claim 1, wherein the loaded liquid solvent obtained from the liquid- liquid extraction contains at least 50% of the amount of said one or more battery metals present in the liquid leachate before the liquid-liquid extraction.

3. The method of claim 1 or 2, wherein the black-mass liquid leachate comprises lithium, and the loaded liquid solvent obtained from the liquid-liquid extraction contains at least 90% of the amount of lithium present in the black-mass liquid leachate before the liquid-liquid extraction.

4. The method of any one of claims 1-3, wherein said stripping is performed in a cascade of at least two stripping units.

5. The method of any one of claims 1-4, wherein said battery metals comprise lithium, cobalt, nickel, or manganese.

6. The method of any one of claims 1-5, wherein said black-mass leachate is obtained from recycling a spent battery selected from at least one of an LFP battery, an LCO battery, an LMO battery, an LMO/LMNO battery, an NCA battery, and an NMC battery.

7. The method of any one of claims 1-6, wherein said black-mass leachate further comprises one or more impurity metal(s).

8. The method of claim 7, wherein said one or more impurity metal(s) is/are selected from one or more of aluminium and copper.

9. The method of any one of claims 1-8, wherein the liquid-liquid extraction is a multi- stage extraction in which at least one extraction stage is performed at a pH providing for an extraction yield of the one or more battery metal(s) of at least 50%.

10. The method of claim 9, wherein said pH is about 3 to 10.

11. The method of any one of claims 1-10, wherein said liquid-liquid extraction is performed with an immiscible liquid solvent / liquid leachate volume ratio from 0.1 to 10.

12. The method of any one of claims 1-11, further comprising a filtration step upstream of the liquid-liquid extraction step in which the battery black-mass liquid leachate undergoes filtration to remove iron.

13. The method of any one of claims 4-12, wherein said cascade of at least two stripping units comprises three striping units operating at a pH of the respective aqueous stripping solution of about 8 to 3, about 7 to 2, and about 6 to 0.

14. The method of any one of claims 1-13, wherein the stripping is performed at a temperature of from about 15°C to about 80°C.

15. The method of any one of claims 1-14, wherein the immiscible liquid solvent used in the liquid-liquid extraction step is lean solvent recycled from the cascade of two or more stripping units.

16. The method of claim 15, wherein said lean solvent is washed prior to being recycled into the liquid-liquid extraction step.

17. The method of any one of claims 1-16, wherein the immiscible liquid solvent comprises di-2-ethylhexyl phosphoric acid (D2EHPA), 2-Ethylhexyl phosphonic acid mono-2-ethylhexylester (PC-88A), bis-2,4,4-trimethylpentyl dithiophosphinic acid (Cyanex 301), bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272), neodecanoic acid (Versatic acid 10), LIX 84, or a mixture thereof.

18. The method of any one of claims 1-17, wherein the battery-grade precursor solution comprises lithium, nickel and lithium, or cobalt and manganese.

19. The method of any one of claims 1-18, wherein battery-grade precursor solution collected from a stripping unit comprises about > 90 mol % Li and about 0-10 mol % Nickel.

20. The method of any one of claims 1-19, wherein battery-grade precursor solution collected from a stripping unit comprises about 20-70 mol % lithium, 20-60 mol % nickel, < 10 mol % manganese, and < 10 mol % cobalt.

21. The method of any one of claims 1-20, wherein battery-grade precursor solution collected from a stripping unit comprises < 10 mol % lithium, < 10 mol % nickel, 30-70 mol % manganese, and > 30 mol % cobalt.

22. The method of any one of claims 1-21, wherein said cathode material is selected from LFP, LCO, LMO, LMO/LMNO, NCA, and NMC.

23. The method of claim 22, wherein said cathode material is selected from one of more of LCO, LFP, LMO/LMNO, NCA80, NCA90, NMC333, NMC 523, NMC532, NMC622, and NMC811.