Recovery of materials from lithium iron phosphate battery waste

Abstract

Methods are provided for forming iron phosphate. In a first stage, heat treating lithium iron phosphate black mass and selectively leaching lithium from the heat treated lithium iron phosphate black mass with an oxidative leaching solution forms a semi-delithiated iron phosphate black mass. In a second stage, the semi-delithiated iron phosphate black mass and a pre-leaching solution comprising dilute acid and an oxidizing agent are mixed, and in a third stage the remaining iron phosphate in the solid phase and an iron phosphate leaching solution are mixed to form a leachate comprising iron phosphate.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Application No. 63 / 704,459, entitled “RECOVERY OF MATERIALS FROM LITHIUM IRON PHOSPHATE BATTERY WASTE”, and filed on Oct. 7, 2024. The entire contents of the above-identified application(s) are hereby incorporated by reference for all purposes.FIELD

[0002] The present description relates generally to methods for recovering materials such as iron phosphate and graphite from spent lithium iron phosphate batteries.BACKGROUND / SUMMARY

[0003] Many technologies, such as electric vehicles and cellphones to name a few, rely on lithium-ion batteries (LIBs). However, LIBs may degrade after a finite number charging / discharging cycles and thus become spent LIBs and demand replacement. Lithium iron phosphate (LFP) is an electroactive material used in cathodes of some LIBs. Compared to the nickel, cobalt, and manganese used in other electroactive materials (e.g., lithium nickel manganese cobalt oxide), the iron of LFP is relatively cheap and abundant. For this reason, recycling of LFP based LIBs has conventionally been directed to recovery of lithium while the remaining iron phosphate and anode material is discarded. However, disposing of iron phosphate may result in contamination of drinking water. Additionally, while iron is an abundant metal, mining of iron is not without environmental consequences. For these reasons, diversion of iron phosphate from landfills and recovery of useful iron phosphate from the battery recycling process is desired.

[0004] In one example, the inventors recognize the issues described above and they may be at least partially addressed by a method for forming iron phosphate, comprising: in a first stage, heat treating lithium iron phosphate black mass to form a heat treated lithium iron phosphate black mass and selectively leaching the heat treated lithium iron phosphate black mass with an oxidative leaching solution to form a semi-delithiated iron phosphate black mass; in a second stage, mixing the semi-delithiated iron phosphate black mass and a pre-leaching solution comprising an acid and an oxidizing agent to form a slurry, and separating the slurry into a solid phase and a liquid phase, the solid phase comprising iron phosphate and graphite and the liquid phase comprising lithium ions and leachate impurities; and in a third stage, mixing the solid phase and an iron phosphate leaching solution to form a leachate comprising iron phosphate and a graphite solid phase. In this way, the iron phosphate may be diverted from a landfill and redirected to battery materials for recycled LFP batteries or for other applications. Additionally, a yield of lithium from the LFP black mass may be increased by recovering lithium from the pre-leach solution. Further, graphite may also be recovered and used as battery anode material.

[0005] It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1A shows a block diagram depicting an overview of stages of recycling lithium iron phosphate (LFP) batteries.

[0007] FIG. 1B shows a chart of composition of a solid phase during the stages of recycling LFP batteries.

[0008] FIG. 2 shows a block diagram depicting an overview of stages of recycling lithium iron phosphate batteries.

[0009] FIG. 3 schematically shows recovery of iron phosphate, residual lithium and graphite from delithiated lithium iron phosphate black mass.

[0010] FIGS. 4A-4B show a flowchart of an example of a method for recovering iron phosphate, residual lithium, and graphite from delithiated lithium iron phosphate black mass.

[0011] FIG. 5 shows a flowchart of an example of a method for recovering lithium from a lithium leachate.

[0012] FIG. 6 shows a flowchart of an example of a method for purifying graphite recovered from the iron phosphate leach solution.

[0013] FIG. 7 shows X-ray diffraction spectra of precipitated iron phosphate under different drying conditions.

[0014] FIG. 8 shows an X-ray diffraction spectrum of hydrothermally precipitated iron phosphate.

[0015] FIG. 9 shows SEM images of hydrothermally precipitated iron phosphate.

[0016] FIG. 10 shows an XRD spectrum of recovered graphite.

[0017] FIG. 11 shows an SEM image of recovered graphite.DETAILED DESCRIPTION

[0018] The following description relates to methods for recovering iron phosphate and graphite in addition to lithium from a recycling stream of lithium iron phosphate (LFP) black mass. The recovery process may be divided into stages as outlined in the block diagram of FIG. 1A. During each stage, different target materials (e.g., lithium, iron phosphate, and graphite) may be separated from each other and from impurities of the LFP black mass. Impurities may include a plurality of different metal ions which may stem from LFP dopants in addition to other metal components of the battery, such as aluminum and / or copper current collectors. The recovery process may include steps wherein either impurities or a target material are selectively partitioned between a solid phase and a liquid phase to recover the desired materials. The process is illustrated as a chart in FIG. 1B showing the relative molar compositions of the solid phase after the stages described in FIG. 1A. A detailed process diagram for recovering the target materials is shown in FIG. 2, and the partitioning is shown schematically in FIG. 3. A flowchart of an example of a method for recovery of iron phosphate is shown in FIGS. 4A-4B. During recovery of iron phosphate, a lithium-containing leachate is produced. A flowchart of an example of a method for recovering lithium from the lithium leachate is shown in FIG. 5. Further, during recovery of iron phosphate a solid phase of graphite including graphite and impurities may be produced. A flowchart of a method for removing impurities from the graphite is shown in FIG. 6. The recovered iron phosphate can be characterized using X-ray diffraction (XRD) as shown in FIG. 7 and FIG. 8 and / or by scanning electron microscope (SEM) as shown in FIG. 9. The recovered graphite can be characterized using XRD as shown in FIG. 10 and / or by SEM as shown in FIG. 11.

[0019] Turning to FIG. 1A, a block diagram 100 is shown outlining stages of an embodiment of the process for recovering iron phosphate, lithium, and graphite from LFP black mass. In stage 1 of this embodiment, LFP black mass 102 is subjected to heat treatment to form heat treated LFP black mass 103. Heat treated LFP black mass is then subjected to selective oxidative lithium leaching to produce semi-delithiated iron phosphate black mass 104. The LFP black mass 102 may be obtained from an LFP battery recycling stream by grinding, crushing, shredding, or otherwise comminuting end-of-life LFP batteries. The LFP black mass may include lithium iron phosphate and graphite, as well as impurities. The process of selective oxidative lithium leaching may partition some but not all of the lithium from the LFP black mass into a leachate and leave behind semi-delithiated iron phosphate black mass 104 in a solid phase. Herein, it is understood that semi-delithiated iron phosphate black mass is comprised of more than iron phosphate and lithium, but “semi-delithiated iron phosphate black mass” is used for brevity.

[0020] In stage 2, for this embodiment, semi-delithiated iron phosphate black mass 104 is subjected to impurity pre-leaching to remove impurities, such as but not limited to lithium, copper, aluminum, cobalt, and magnesium ions. Impurity pre-leaching leaves behind iron phosphate black mass 106 as a solid phase material. Iron phosphate black mass 106 may comprise a mixture of iron phosphate and graphite along with graphite impurities. In a third stage, for this embodiment, iron phosphate black mass 106 is separated into iron phosphate 108 and graphite 110 via a process of iron phosphate leaching.

[0021] Turning to FIG. 1B, chart 150 schematically shows relative molar compositions of the solid phase after the stages described above with respect to FIG. 1A. Bars 152 correspond to the solid composition prior to stage 1, before the recovery process. In other words, bars 152 may be reflective of a composition of the LFP black mass. In the LFP black mass, a molar ratio of lithium to iron phosphate may be approximately (e.g., + / −5%) 1:1. The LFP black mass may further include graphite, shown in the hashed bar, and impurities, shown in the dotted bar.

[0022] Bars 154 correspond to the solid phase after stage 1 is finished. Stage 1 includes selective oxidative lithium leaching. For this reason, the open bar corresponding to lithium component is decreased compared to pre-stage 1 and the remainder of bars 154 are essentially unchanged. Pre-stage 1, a molar ratio of lithium to iron phosphate is greater than a molar ratio of lithium to iron phosphate post-stage 1. Bars 156 correspond to the solid phase after stage 2. Stage 2 includes pre-leaching impurities. By pre-leaching impurities, both impurities and the remainder of the lithium may be selectively leached into the liquid phase, leaving behind the iron phosphate and graphite in the solid phase. The moles of lithium phosphate and graphite in the solid phase may not be substantially changed by pre-leaching impurities. Pre-leaching in the second stage may remove at least 75% of impurities from the semi-delithiated iron phosphate black mass, being leached into the impurity leachate. Bar 158 corresponds to the solid phase after stage 3. Stage 3 includes iron phosphate leaching. Iron phosphate leaching partitions substantially all of the iron phosphate into the liquid phase after stage 3 leaving behind graphite as shown by the hashed bar. By staging the extraction steps in this way, iron phosphate leaching does not demand selectivity from the impurities and further extraction steps to remove impurities after iron phosphate leaching are not demanded.

[0023] Turning to FIG. 2, a process flow diagram 200 of a specific embodiment for carrying out stages 1-3 for recovery of lithium, iron phosphate, and graphite is shown. As shown, LFP black mass 201 is heat treated to form heat treated LFP black mass 202. Heat treated LFP black mass 201 and oxidative leaching solution 204 are then combined with oxidative leaching solution 204 selectively leaching lithium from the LFP black mass. The mixture undergoes solid / liquid separation to produce lithium leachate 206 (liquid phase) and semi-delithiated iron phosphate black mass 210 (solid phase). The lithium leachate may then be subjected to further processing to produce a lithium salt 208. Lithium salt 208 may then be reused in the synthesis of a cathode active material for lithium-ion batteries.

[0024] Semi-delithiated iron phosphate black mass 210 and pre-leach solution 212 are then combined, with pre-leach solution 212 leaching remaining lithium ions and impurity ions from semi-delithiated iron phosphate black mass 210. The mixture undergoes solid liquid separation to produce impurity leachate 214 (liquid phase) and iron phosphate black mass 218 (solid phase). Impurity leachate 214 may include both impurity ions and lithium ions. The impurity leachate 214 may be subjected to further processing as described below with respect to FIG. 5 to separate lithium ions from the impurities and produce lithium salt 216. Lithium salt 216 may then be reused in the synthesis of cathode active material for lithium-ion batteries.

[0025] Iron phosphate black mass 218 and iron phosphate leaching solution 220 are then combined, and the mixture is separated to produce iron phosphate leachate 226 (liquid phase) and graphite 222 (solid phase). Graphite 222 may undergo further processing as described below with respect to FIG. 6 to remove remaining impurities and produce purified graphite 224. Iron phosphate leachate 226 may undergo further processing to produce iron phosphate crystals 228. Further processing may include chemically induced precipitation and crystallization or hydrothermal processing.

[0026] As described above, the process of recovering materials from LFP black mass includes a series of stages wherein different elements are selectively partitioned between a liquid phase and solid phase. Turning to FIG. 3, the partitioning is shown schematically. A first mixture 300 is shown including a pre-leaching solution 302 and a semi-delithiated iron phosphate black mass 304. The pre-leaching solution 302 may include an acid and an oxidizing agent and is preferably a dilute aqueous acidic solution comprising an oxidizing agent, while the semi-delithiated iron phosphate black mass 304 may include graphite, lithium ions, iron phosphate and impurities. After mixing for a duration, a second mixture 306 is obtained. In second mixture 306, remaining lithium ions and impurities are partitioned into impurity leachate 308 in a liquid phase and iron phosphate black mass 310 in a solid phase. Iron phosphate black mass 310 may include iron phosphate and graphite. First mixture 300 and second mixture 306 may be examples of pre- and post-stage 2 respectively as described above with respect to FIG. 1A.

[0027] Impurity leachate 308 and iron phosphate black mass 310 may be separated and the impurity leachate replaced with iron phosphate leaching solution 314 to form third mixture 312. The iron phosphate leaching solution may include a strong acid and oxidizing agent. After mixing for a duration, fourth mixture 316 is obtained. In fourth mixture 316, ferric ions and phosphate ions are partitioned into iron phosphate leachate 320, leaving graphite 318 in a solid phase. Third mixture 312 and fourth mixture 316 may be examples of pre- and post-stage 3 respectively as described above with respect to FIG. 1A. In this way, by selecting compositions of leaching solutions, impurities may be leached into a solution in a separate stage from leaching iron phosphate. Leaching impurities and iron phosphate in two different stages allows for separation of the two, whereas if impurities and iron phosphate are leached at the same time, the chemical similarities between iron phosphate and the phosphate impurities may make further downstream separation difficult.

[0028] Turning to FIG. 4A, a flowchart of a method 400 for recovering iron phosphate from LFP black mass is shown. The method may include steps to carry out the three stages as described above with respect to FIG. 1A. At 401, method 400 includes heat treating the LFP black mass. The LFP black mass may be obtained, for example, by shredding LFP secondary batteries and may include Al and Cu from current collectors in addition to anode and cathode active materials and metal impurities, such as from dopants, coatings, and / or handling and processing contamination. Heat treating may include heating the LFP black mass in an inert environment (e.g., N2 or Ar gas) and at a temperature that is capable of volatilizing and removing organic solvent and binder polymer coatings from the LFP black mass. Heat treating may include treating in a temperature range of from 500° C. to 670° C. In this way, significant impurities are removed from the LFP black mass prior to any leaching removal steps.

[0029] At 402, method 400 includes mixing heat treated LFP black mass and an oxidative leaching solution to form a lithium leachate and a semi-delithiated iron phosphate black mass. The oxidative leaching solution may include at least one oxidant, including, for example peroxides, persulfates, sulfates, hypoclorites, chlorites, chlorates, perchlorates, nitrates, nitrous oxide, nitrogen dioxide, and halogens (Cl2, Br2, I2). The oxidative leaching solution may further include at least one acid. In one example, the at least one acid may be an inorganic acid (such as sulfuric, hydrochloric, nitric or phosphoric acid) or an organic acid (including mono-carboxylic or dicarboxylic acids). Other suitable acids and oxidizing agents may also be introduced. The leachate resulting at step 402 may include leached lithium ions, and the semi-delithiated iron phosphate black mass formed may include iron phosphate, residual lithium ions, graphite, and remaining impurities.

[0030] At 404, method 400 includes separating the semi-delithiated iron phosphate black mass and the lithium leachate. The lithium leachate may be directed to a process for recovering the lithium salt from the lithium leachate.

[0031] At 406, method 400 includes mixing the semi-delithiated iron phosphate black mass and a pre-leaching solution to form an impurity leachate and iron phosphate black mass. The pre-leaching solution may include an acid and an oxidizing agent, such as a dilute aqueous acid solution comprising an oxidizing agent. Iron phosphate preferably has a very low solubility in the pre-leaching solution while the solubility of metal oxide impurities and remaining lithium in the pre-leaching solution is preferably very high. The oxidizing agent of the pre-leaching solution may oxidize soluble ferrous hydrogen phosphate to less soluble iron phosphate.

[0032] In some examples, the acid included in the pre-leaching solution may be an inorganic acid. In further examples, the acid may be sulfuric acid. The concentration of the acid in the pre-leaching solution may be in a range of from 0.2M to 0.6M. In further examples, the concentration of the acid may be in a range of from 0.3M to 0.5M, such as 0.4M. The oxidizing agent of the pre-leaching solution may be any of those described above for the oxidative leaching solution, including, for example, one or more of a peroxide, a persulfate, a hypochlorite, a perchlorate, a nitrate, nitrous oxide, and nitrogen dioxide. The concentration of the oxidizing agent in the pre-leaching solution may be in a range of from 0.1% to 10% by weight, such as from 2% to 5%.

[0033] The amount of the pre-leaching solution relative to the amount of the semi-delithiated iron phosphate black mass will depend on the concentration of the acid and the concentration of the oxidizing agent in the solution. In general, the more dilute the pre-leaching solution is in either the acid or the oxidizing agent, the higher the ratio of the pre-leaching solution to the semi-delithiated black mass. For example, when the concentration of the acid in the pre-leaching solution is in the range of from 0.2M to 0.6M, the liquid / solid ratio of the pre-leaching solution to the semi-delithiated iron phosphate black mass can be from 2 to 10 mL / g. During leaching, the temperature of the pre-leaching solution may be maintained within a range of from 20° C. to 80° C. In some examples, the temperature may be in a range of from 30° C. to 70° C. In further examples, the temperature may be in a range of from 50° C. to 70° C. Additionally, mixing the semi-delithiated iron phosphate black mass with the pre-leaching solution may include mixing for a duration in a range of from 2 hours to 8 hours.

[0034] Furthermore, in some embodiments, the pre-leaching solution may be provided in two parts, with a first part including the acid and a second part including some or all of the oxidizing agent. For example, the semi-delithiated iron phosphate black mass and a first part of the pre-leaching solution including the acid may be combined first followed by addition of a second part including the oxidizing agent. In this way, greater control over maintaining the desired oxidation state of iron can result. The ratio of the parts can be varied based on ease of processing. For example, it may be preferable to first combine the semi-delithiated black mass and a first part including the acid followed addition of the second part including the oxidizing agent, wherein the volume of the first part is greater than the volume of the second part. Using the larger part first would assist in mixing when the second part is added.

[0035] At 408, method 400 includes separating the resulting iron phosphate black mass and the impurity leachate. As described above in FIG. 2, the impurity leachate may be directed to a process for lithium recovery as detailed further below with respect to FIG. 5. At 410, the level of impurities in the iron phosphate black mass is determined and compared to a target threshold level. If the level of impurities is not below the target threshold level, the iron phosphate black mass and an additional pre-leaching solution may be combined using the same or different conditions as needed to achieve the target threshold level.

[0036] In a specific example, 100 grams of a semi-delithiated black mass, prepared as described herein, was dispersed in 500 mL of a 0.4M sulfuric acid solution with mechanical stirring. The temperature was increased to 60° C., and 50 mL of a 35% hydrogen peroxide solution was added dropwise over one hour to this reaction mixture, which was allowed to stir at 60° C. for 5 hours. The resulting iron phosphate black mass and the impurity leachate were then separated, and the iron phosphate black mass was rinsed multiple times with DI water. This process was repeated a second time under the same conditions.

[0037] Table 1 below shows the impurity levels present in the starting semi-delithiated black mass as well as in the iron phosphate black mass produced after each pre-leaching. A percent removal is also calculated. Impurity levels (mg / kg) were determined by quantitative inductively coupled plasma-optical emission spectroscopy (ICP-OES).TABLE 1Percent removal of impurities from semi-delithiated iron phosphateblack mass by sequential pre-leaching solutions.IronIronSemi-phosphate% Im-phosphate% Im-Im-delithiatedBM after1stpurityBM after 2ndpuritypurityBMPre-leachRemovalPre-leachRemovalFe23208120000413%217129 6%P12705110268019%11178712%Li7951105486%35596%Ni231637783%21891%Mn1894156717%97049%Co87530066%19178%Cu799185089%24597%Al203439481%2599%Na4482N / AN / A50889%Ca622166%1477%Mg1379123111%99328%Cr19615421%11442%Zn115110 4%8724%Zr61887%887%Ti89340455%32364%As shown above in Table 1, the pre-leaching solutions removed substantial quantities of impurities ions such as cobalt, copper, aluminum, sodium, and calcium while the amounts of iron and phosphorus decrease by less than 20%, indicating minimal loss of iron phosphate.

[0038] Upon achieving impurity levels in the iron phosphate black mass that are below target threshold levels, method 400 proceeds to 412 as continued in FIG. 4B and includes mixing the iron phosphate black mass and an iron phosphate leaching solution to form an iron phosphate leachate and a crude graphite. The iron phosphate leaching solution may be a concentrated (high molarity) acid solution. The concentration of acid in the iron phosphate leaching solution may be higher than the acid concentration of the pre-leaching solution. In some examples, the acid included in the iron phosphate leaching solution may be an inorganic acid. In further examples, the acid included in the iron phosphate leaching solution may be sulfuric acid. As one example, the concentration of the acid may be in a range of from 1M to 5 M. In further examples, the acid concentration may be in a range of from 2 M to 5 M. In further examples, the acid concentration may be in a range of from 2 M to 3 M. The iron phosphate black mass and the iron phosphate leaching solution may be combined at a volume / weight ratio of from 3:1 to 15:1 (mL iron phosphate leach solution to grams iron phosphate black mass). In further examples, the ratio may be from 6:1 to 12:1, such as from 8:1 to 12:1. The temperature of the mixture may be maintained within a range of from 20° C. to 90° C. In further examples, the temperature may be in a range of from 65° C. to 85° C., including, for example 80° C. In some examples, the iron phosphate black mass and the iron phosphate leaching solution may be mixed for 1 hour up to 10 hours. In some examples, the mixing duration may be in range of from 3 hours to 8 hours. In further examples, the mixing duration may be in range of from 4 hours to 6 hours.

[0039] In a specific example, 100 grams of iron phosphate black mass, prepared as described above, was dispersed in 1 L of a 2.5 M sulfuric acid iron phosphate leaching solution with mechanical stirring. The reaction mixture was heated to 80° C. and stirred for 5 hours at this temperature. The resulting iron phosphate leachate and graphite were separated by filtration with a 1 micron filter membrane. Table 2 below shows the composition of the filtered iron phosphate leachate as determined by ICP-OES.TABLE 2Composition of filtered iron phosphate leachate (mg / L)FePLiNiMnCoCuAlNaCaMgCrZnZrTi18063N / A27117715135142991280.826

[0040] As shown in Table 2, the iron phosphate leachate is composed primarily of iron with some residual presence of impurity ions. Because impurity ions are present in the iron phosphate black mass before iron phosphate leaching, the impurities may also be carried into the iron phosphate leachate. In this way, pre-leaching may minimize the amount of impurities in the iron phosphate leach solution by partitioning the impurities away before the iron phosphate leaching solution is introduced.

[0041] At 413, method 400 includes separating the iron phosphate leachate and the graphite. The graphite may be further purified as described below with respect to FIG. 6. For example, at 414, iron phosphate may be precipitated from the iron phosphate leachate to form an iron phosphate precipitate. In some examples, precipitating at 414 may include chemical precipitation 416. Chemical precipitation of iron phosphate may include adjusting the pH of the iron phosphate leachate by adding a base and an oxidant to the iron phosphate leachate. The base may raise the pH to a target pH while the oxidant may help ensure the precipitate is in the form of ferric phosphate. As one example, the target pH may be between 1 and 3. In general, when the pH is greater than 3, iron phosphate precipitation rates would be fast, risking non-selective metal phosphate / hydroxide precipitation, including impurity metals. As such, in a specific example, the target pH is slowly adjusted to 2. Adding the base and oxidant may include slowly adding a base, such as sodium hydroxide, to the iron phosphate leachate until the iron phosphate leachate reaches a pH of 1. An oxidant solution, such as hydrogen peroxide can then be added dropwise before continuing the addition until precipitation is complete. In some examples, 5 mL to 20 mL of 35% hydrogen peroxide may be added per 500 mL of iron phosphate leachate.

[0042] The iron phosphate precipitate collected from chemical precipitation may be amorphous. The amorphous iron phosphate precipitate may be dried of moisture at 80° C. and then subjected to further high temperature annealing to convert the amorphous iron phosphate to crystalline iron phosphate. As one example, the dried amorphous iron phosphate may be annealed at a temperature of from 120° C. to 500° C. and for a duration in a range of from 3 hours to 12 hours.

[0043] XRD spectra of chemically precipitated iron phosphate are shown in FIG. 7. Graph 700 shows XRD spectrum 702 of iron phosphate dried at 80° C. for 15 hours. As can be seen, XRD spectrum 702 is very broad and does not include a distinct peak, indicating that the iron phosphate is still amorphous. By comparison, graph 706 shows XRD spectrum 708 of chemically precipitated iron phosphate after drying at 80° C. for three days. XRD spectrum 708 includes some sharp peaks and a broad underlying peak. The combination of broad and sharp peaks indicates that the iron phosphate is a mixture of amorphous and crystalline forms. Graph 710 shows XRD spectrum 712 of chemically precipitated iron phosphate heated at 500° C. for 5 hours. XRD spectrum 712 includes narrow, sharp peaks but does not include a broad baseline, indicating the iron phosphate is substantially fully crystalline.

[0044] Returning to FIG. 4B, in alternate examples, precipitating iron phosphate at 414 may include, at 418, hydrothermal precipitation of the iron phosphate. Hydrothermal precipitation may include increasing the pH of the iron phosphate leachate by adding a strong base. The pH may be increased to a level at which iron phosphate first starts to precipitate at ambient temperatures and pressure. For example, the pH may be increased to about 0.8. The hydrothermal reaction may then be carried out under increased pressure by sealing the iron phosphate leachate in a bomb reactor held at 150° C. for a heating duration in a range of from 1 hour to 10 hours. The resulting iron phosphate crystals may be separated from the remaining leachate after heating and rinsed with an acidic rinse solution followed by drying (e.g., at 80° C.).

[0045] FIGS. 8-9 show a characterization of a hydrothermally precipitated iron phosphate. For example, FIG. 8 shows a graph 800 including XRD spectrum 802, which corresponds to iron phosphate prepared by hydrothermal precipitation as described above. XRD spectrum 802 includes sharp peaks indicating that the iron phosphate is crystalline. FIG. 9 shows SEM images 900 and 902 of hydrothermally precipitated iron phosphate, also indicating that crystalline iron phosphate (FePO4·2H2O) is produced. ICP-OES analysis, shown in Table 3, confirms the purity of the precipitate.TABLE 3Composition of iron phosphate precipitate (mg / kg)FePLiNiMnCoCuAlNaSCaMgCrZnZrSiTiChem.257834143504113961671953526581275412302811731216437Hydro273671162756723819011626101234573112110715217614Thus, the precipitated iron phosphate recovered at the end of method 400 may be crystalline material of sufficient purity for use as a precursor for LFP cathode active material.

[0046] In addition to recovering the iron phosphate, lithium salts may also be recovered from the impurity leachate. As shown in FIG. 5, a method 500 is shown for recovering lithium salts from the impurity leachate. At 502, method 500 includes increasing the pH of the impurity leachate to precipitate leachate impurities, particularly non-lithium impurities by hydrolysis. In one example, increasing the pH may include increasing the pH by adding a base, such as a strong base. In one example increasing the pH may include increasing the pH to a range of from 11 to 12. In an alternate example, increasing the pH may include increasing the pH to a range of from 7 to 9. Optionally, method 500 includes, at 504, combining the impurity leachate and an ion exchange resin to remove additional non-Li impurities, such as cationic impurities, and increase the pH. As one example, step 504 may be performed after raising the pH of the impurity leachate to a range of from 7 to 9. In some examples, the ion exchange resin may be a weakly acidic resin configured to extract divalent and trivalent cations. In some examples, pH of the impurity leachate may be further raised to a range of from 11 to 12 to precipitate further impurities by hydrolysis.

[0047] At 506, method 500 includes concentrating the impurity leachate. In one example, concentrating the impurity leachate may include concentrating by substantially seven times. Concentrating may increase lithium concentration in the impurity leachate to a practical recovery range. Concentration may include removing water from the leachate. For example, concentration may include evaporating the water by heat and / or vacuum.

[0048] At 508, method 500 includes reducing the temperature of the concentrated impurity leachate to crystalize sodium sulfate (e.g., a sodium sulfate precipitation). Sulfate ions may be present from sulfuric acid used in the pre-leaching solution. Sodium ions may be present from sodium hydroxide used to raise the pH of the impurity leachate in step 504. In some examples, reducing the temperature includes reducing the temperature to be in a range of from 0° C. to 5° C.

[0049] At 510, method 500 includes separating the crystalline sodium sulfate and the concentrated impurity leachate. At 512, method 500 includes adding a precipitation reagent to the concentrated impurity leachate to precipitate lithium as a lithium salt. In one example, the precipitation reagent may be one or more of a carbonate, fluoride, phosphate, and oxylate. In further examples, the precipitation reagent may be one or more of sodium carbonate, sodium phosphate, phosphoric acid, sodium fluoride, sodium oxalate, and oxalic acid. In one example, the impurity leachate may be heated above room temperature. In further examples, the impurity leachate may be heated to be in a range of from 90° C. to 95° C. Method 500 ends.

[0050] In addition to iron phosphate and lithium, graphite may also be recovered from LFP black mass. As described above, after iron phosphate is leached from the iron phosphate and graphite mixture, graphite is left behind in the solid phase. The graphite directly following iron phosphate leaching may include residual iron phosphate and other impurities and further purification is demanded to obtain graphite that may be repurposed in a variety of applications.

[0051] Turning to FIG. 6, a method 600 for further purifying graphite obtained from LFP black mass is shown. At 602, method 600 includes mixing graphite and a dilute acid to form leached graphite. The graphite may be graphite remaining after step 413 of method 400 as described above. In one example, the dilute acid may be a dilute inorganic acid solution. In further examples, the dilute acid may be a dilute sulfuric acid solution. In one example, a concentration of the dilute acid may be in a range of from 0.5M to 2M. At 604, method 600 includes separating the leached graphite and the dilute acid. The dilute acid may leach remaining impurities into the liquid phase. In this way, the elemental purity of the leached graphite may be higher than the graphite obtained directly following iron phosphate leaching. At 606, method 600 includes drying the leached graphite. As one example, drying may include drying at a temperature in a range of from 100° C. to 300° C. Method 600 ends.

[0052] In one example, a dried leached graphite recovered at the conclusion of method 600 is tested for purity by ICP-OES and by an ash test. Together, these elemental analyses and ash tests show that the graphite is >99% pure. The dried leached graphite can be further characterized by XRD and SEM, as shown in FIGS. 10-11. Graph 1000 shown in FIG. 10 includes an XRD spectrum 1002. The peaks and relative intensities of XRD spectrum 1002 are indicative of substantially pure graphite. Image 1100 shown in FIG. 11 is typical of recovered graphite.

[0053] The technical effect of the methods described herein is to recover iron phosphate, lithium, and graphite from a waste stream of lithium iron phosphate batteries. The methods may separate the materials of value (e.g., iron phosphate, lithium, and graphite) from impurities efficiently and effectively to provide the materials of value in desired purities. In doing so, end-of-life LFP battery material may be diverted from a landfill.

[0054] The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.

Claims

1. A method for forming iron phosphate, comprising:in a first stage, heat treating lithium iron phosphate black mass to form a heat treated lithium iron phosphate black mass and selectively leaching lithium from the heat treated lithium iron phosphate black mass with an oxidative leaching solution to form a semi-delithiated iron phosphate black mass;in a second stage, mixing the semi-delithiated iron phosphate black mass and a pre-leaching solution comprising an acid and an oxidizing agent to form a slurry, and separating the slurry into a solid phase and a liquid phase, the solid phase comprising iron phosphate and graphite and the liquid phase comprising lithium ions and leachate impurities; andin a third stage, mixing the solid phase and an iron phosphate leaching solution to form a leachate comprising iron phosphate and a graphite solid phase.

2. The method of claim 1, wherein the oxidative leaching solution includes at least one oxidant and at least one acid.

3. The method of claim 1, wherein mixing to form the slurry in the second stage comprises mixing at a temperature range of from 20° C. to 80° C.

4. The method of claim 1, wherein mixing the solid phase and the iron phosphate leaching solution in the third stage comprises mixing at a temperature range of from 20° C. to 90° C.

5. The method of claim 1, further comprising, after the third stage, mixing the graphite remaining in the solid phase and a dilute acid to remove graphite impurities from the graphite.

6. The method of claim 1, further comprising, after the second stage, separating the lithium ions and the leachate impurities of the liquid phase by one or more of hydrolysis, sodium sulfate precipitation, and ion exchange.

7. The method of claim 1, wherein the leachate impurities comprise one or more of nickel, manganese, cobalt, copper, and aluminum.

8. The method of claim 1, wherein the second stage removes at least 75% of the leachate impurities from the semi-delithiated iron phosphate black mass.

9. The method of claim 1, wherein the acid of the pre-leaching solution is an inorganic acid.

10. The method of claim 1, wherein the oxidizing agent of the pre-leaching solution is one or more of a peroxide, a persulfate, a hypochlorite, a perchlorate, a nitrate, a nitrous oxide, and a nitrogen dioxide.

11. The method of claim 1, wherein a concentration of the acid comprising the pre-leaching solution is in a range of from 0.2 M to 0.6 M.

12. The method of claim 1, wherein a molar ratio of lithium to iron in the heat treated lithium iron phosphate black mass is greater than a molar ratio of lithium to iron in the semi-delithiated iron phosphate black mass.

13. The method of claim 1, wherein the iron phosphate leaching solution comprises a concentrated acid solution comprised of an inorganic acid in a range of from 2 M to 5 M.

14. A method for forming iron phosphate, comprising:heat treating a lithium iron phosphate (LFP) black mass to form a heat treated LFP black mass;mixing the heat treated LFP black mass and an oxidative leaching solution to form a lithium leachate and a semi-delithiated iron phosphate black mass;separating the semi-delithiated iron phosphate black mass and the lithium leachate;mixing the semi-delithiated iron phosphate black mass and a pre-leaching solution to form an impurity leachate and an iron phosphate black mass;separating the impurity leachate and the iron phosphate black mass;mixing the iron phosphate black mass and an iron phosphate leaching solution to form an iron phosphate leachate and graphite; andprecipitating iron phosphate from the iron phosphate leachate.

15. The method of claim 14, wherein the impurity leachate comprises lithium ions.

16. The method of claim 14, wherein the method further comprises removing impurities from the impurity leachate by one or more of hydrolysis, ion exchange, and / or sodium sulfate precipitation, and precipitating a lithium salt from the impurity leachate.

17. A method for forming iron phosphate, comprising:selectively leaching a lithium iron phosphate black mass and an oxidative leaching solution to form a semi-delithiated iron phosphate black mass;mixing the semi-delithiated iron phosphate black mass and a pre-leaching solution to pre-leach impurities from the semi-delithiated iron phosphate black mass and obtain an iron phosphate black mass;leaching iron phosphate from the iron phosphate black mass to form an iron phosphate leachate; andprecipitating iron phosphate from the iron phosphate leachate to form an iron phosphate precipitate.

18. The method of claim 17, wherein precipitating iron phosphate comprises chemically precipitating by adjusting a pH of the iron phosphate leachate by adding a base and an oxidizing agent.

19. The method of claim 17, further comprising annealing the iron phosphate precipitate to form a crystalline iron phosphate.

20. The method of claim 17, wherein precipitating iron phosphate comprises increasing a pH of the iron phosphate leachate and hydrothermally precipitating the iron phosphate leachate.

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