Recycling method for recovering lithium from a material containing lithium and one or more transition metals

Abstract

1. A method for recycling lithium from an input material comprising lithium and one or more transition metals, the method comprising the steps of contacting the input material with a leach medium comprising an organic acid, leaching lithium from the input material to form a leachate comprising an organic lithium salt, and electrolytically converting the organic lithium salt to an inorganic lithium salt in an electrochemical cell.

Description

[Technical field]

[0001] The present specification relates to a recycling method for recovering lithium from materials containing lithium and one or more transition metals, the method being particularly suitable for recovering lithium from waste battery materials, including so-called "black nugget". [Background technology]

[0002] The number of portable electronic devices (such as smartphones and laptops) that require rechargeable batteries is increasing every year. Due to growing environmental concerns, the automotive industry is looking for alternatives to internal combustion engines, and rechargeable batteries are one solution. With consumers increasingly accepting hybrid and fully electric vehicles powered by rechargeable batteries, it is reasonable to expect that the global demand for rechargeable batteries will increase.

[0003] Modern rechargeable batteries typically contain cathode materials based on transition metal oxide frameworks with intercalated lithium. Examples include LiCoO2, LiMn2O4, LiFePO4, LiNiCoAlO2, and LiNi x Mn y Co z O2 ("NMC"). One promising material for automotive applications is "NMC" (lithium-nickel-manganese-cobalt), which has the general formula LiNi x Mn y Co z O2, where x+y+z=1. It is desirable to provide a route to recover and recycle the metals used in battery cathode materials. This is particularly important for Co, Ni, and Li, and to a lesser extent Mn.

[0004] The recovery of Li, Ni, Mn, and Co from NMC materials has been previously studied. In a typical process, metals are solubilized from the cathode scrap (e.g., the so-called "black mass") by using an acidic leaching medium (e.g., sulfuric acid) to form a leachate containing the metal ions, which are then separated by a series of precipitations using pH adjustment and / or solvent extraction. Fe, Al, and Cu can be removed from the leachate by various methods, including sulfidation, or precipitation using NaOH. Mn, Co, and Ni are typically separated from the leachate by precipitation and / or solvent extraction, but are often contaminated with Li impurities. Li is usually the last material remaining in solution, and is precipitated, for example, as Li2CO3. However, at this stage the leachate still contains sodium ions that were introduced when precipitating Fe, Al, and Cu, and during solvent extraction. Precipitation of Li often uses Na2CO3 as the carbonate source, which easily produces Li2CO3 contaminated with Na2CO3, from which high purity Li is difficult to obtain. It would therefore be advantageous to remove Li from the cathode scrap prior to leaching and separation of transition metal components such as Ni, Co, and Mn.

[0005] To provide a more direct recycling route, particularly for Li-ion battery scrap, it would be advantageous to provide a method that can selectively remove Li from the solid starting material prior to extracting and separating one or more transition metal components from the solid starting material. This specification addresses this problem. Summary of the Invention

[0006] Provided herein is a method for recycling lithium from an input material comprising lithium and one or more transition metals, comprising the steps of: contacting the input material with a leach medium comprising an organic acid; leaching lithium from the input material to form a leachate comprising an organic lithium salt; and electrolytically converting the organic lithium salt to an inorganic lithium salt in an electrochemical cell.

[0007] Preferably, the organic acid in the leaching medium is formic acid. In this case, the organic lithium salt in the leaching solution is in the form of lithium formate, which is converted in the electrochemical cell to an inorganic lithium salt. The inorganic lithium salt may be lithium hydroxide or lithium carbonate.

[0008] The steps of contacting the input material and leaching lithium from the input material to form a leachate comprising an organic lithium salt such as lithium formate are described in the patentee's earlier UK patent application No. 2016329.1, filed on October 15, 2020. For example, it has been established that Li can be selectively leached from the input material if the concentration of formic acid in the leaching medium is sufficiently high. Without wishing to be bound by any theory, it is believed that the high selectivity for leaching of Li is a result of the poor solubility of transition metals in high concentrations of formic acid. In contrast, Li ions are highly soluble in formic acid and form soluble lithium formate in situ. Previous reports of separating these metals from NMC cathode scrap have only explored the use of dilute formic acid under conditions where Ni(II), Co(II), and Mn(II) have significant solubility in the leaching medium.

[0009] For example, selective formic acid leaching of lithium from black mass produces a highly concentrated aqueous formic acid solution that contains mainly lithium with low concentrations of other metals. For the lithium extraction approach to be economically and environmentally viable as a recycling method, it is desirable to convert the lithium formate in this solution to high purity lithium hydroxide or lithium carbonate for reuse in the synthesis of cathode materials for lithium-ion batteries, and to recycle the formic acid for reuse in the leaching step of the recycling process. This specification builds on the work described in UK Patent Application No. 2016329.1 by providing a further process for the electrolytic conversion of organic lithium salts (e.g., lithium formate) in the leachate to inorganic lithium salts such as lithium hydroxide to enable this requirement. To achieve this function, several different electrochemical processing methods and cell configurations are described herein. According to certain embodiments, the electrochemical processing methods and cell configurations use one or more membranes that are selective for the permeation of monovalent lithium over the permeation of multivalent transition metals, for example under certain pH conditions or due to a special design of the membrane. In this case, such an electrochemical cell configuration and method is capable of both separating lithium from multivalent transition metal impurities in the leachate and converting lithium formate to an inorganic lithium salt such as lithium hydroxide. Alternatively, or in addition, a multivalent metal separation step (such as an ion exchange process) may be applied to the leachate prior to electrolysis. In this case, the use of a selective membrane is not necessarily required in the electrochemical cell configuration, and only the conversion of lithium formate to lithium hydroxide is required.

[0010] Although the electrochemical processing techniques are described in the context of using formic acid, particularly concentrated formic acid, as the organic acid for leaching lithium from the input material, the same electrochemical processing techniques are applicable when using a different organic acid for the leaching step. Examples of organic acids for the leaching process include formic acid, acetic acid, propionic acid, malonic acid, citric acid, butyric acid, oxalic acid, tartaric acid, or a mixture of two or more of these organic acids. Furthermore, while the inorganic lithium salt is preferably lithium hydroxide, it is possible to produce other inorganic lithium salts. For example, lithium carbonate can be formed electrochemically.

[0011] Advantageously, the electrochemical methods and cell configurations described herein are tailored to reduce oxidation of formate (or other organic acid derivatives, if other organic acids are used in the leaching medium) in the electrochemical cell, allowing a significant portion of the organic acid (e.g., formic acid) to be regenerated and recycled from the electrochemical cell for reuse in the leaching process. For example, at least 50%, 60%, 70%, 80%, or 90% by weight of the organic acid in the leaching medium can be recycled from the electrochemical cell.

[0012] In certain configurations, the lithium hydroxide produced in the electrochemical cell comprises a mixture of hydroxide and formate (or other organic acid derivative). In this case, advantageously, the method further comprises selectively precipitating lithium hydroxide (or other inorganic lithium salt) from the mixture at a temperature of at least 60°C, 70°C, 80°C, 90°C, or 100°C. The supernatant from the precipitation can be recycled to the electrochemical cell to recycle the formate (or other organic acid derivative) and also to extract any additional lithium remaining in the supernatant. The precipitated lithium hydroxide can be washed and the resulting washing solution also recycled through the electrochemical cell, again ensuring increased lithium extraction and minimizing formate loss from the system. The lithium hydroxide can then be dried for use in the manufacture of new lithium-containing functional materials, such as cathode materials for lithium-ion batteries. Water evaporated during processing (e.g., in the drying step and / or during precipitation) can also be recycled back into the system, for example, for reuse in the washing step.

[0013] The electrochemical cell can be designed to selectively extract lithium from the leachate over transition metal impurities therein. For example, the electrochemical cell can include a diluent chamber for receiving the leachate and a concentrate chamber separated from the diluent chamber by a cation exchange membrane that blocks multivalent transition metals and selectively allows lithium ions to pass through the diluent chamber into the concentrate chamber to form lithium hydroxide in the concentrate chamber. A pH gradient is maintained across the operating cation exchange membrane, which ensures the monovalent selectivity of the cation exchange membrane and significantly reduces the flux of multivalent ions through the membrane. The pH gradient also reduces the flux of uncharged molecules, such as molecular formic acid, through the membrane. Multivalent transition metals accumulate on the cation exchange membrane during operation, but can be periodically removed from the cation exchange membrane by chemically stripping or periodically reversing the cell current. Alternatively, if a dedicated monovalent selective cation exchange membrane (i.e., a permselective cation exchange membrane for monovalent ions) is used, the monovalent selectivity can be based on 2+ charge repulsion rather than a pH gradient.

[0014] One way to reduce the oxidation of formate (or oxidation of other organic acid derivatives) in the electrochemical cell described above is to provide a configuration further including one or more bipolar membranes. For example, a bipolar membrane can be provided adjacent each of the diluent and concentrate chambers, separating the chambers from the anode / anolyte and cathode / catholyte. That is, the electrochemical cell can include an anolyte chamber in contact with the anode, the anolyte chamber being separated from the diluent chamber adjacent to the anolyte chamber by a bipolar membrane, and the electrochemical cell can further include a catholyte chamber in contact with the cathode, the catholyte chamber being separated from the concentrate chamber adjacent to the catholyte chamber by a bipolar membrane. Alternatively, a single bipolar membrane can be provided adjacent to the diluent chamber to limit oxidation. Alternatively, or in addition, a suitable anode material can be selected that is incapable of performing organic acid (e.g., formic acid) oxidation, thus minimizing organic acid loss.

[0015] Advantageously, a plurality of diluent and concentrate chamber pairs are provided, each pair being separated by a bipolar membrane. Such an arrangement thus comprises a series of repeating units separated by a bipolar membrane, each repeating unit comprising a diluent chamber for receiving a leachate and a concentrate chamber in which lithium hydroxide is formed. The electrochemical cell comprises at least 3, 4, 6, 8, 10, 15, 20, 50, 100, 200, 300 or 350 (e.g. up to 400 or 500) pairs of diluent and concentrate chambers.

[0016] The use of a bipolar membrane allows the majority of protons formed in the electrolysis to be generated by water dissociation rather than hydroxylation, thereby significantly slowing down the rate of oxidation of formic acid.

[0017] Alternatively, it is possible to design a cell configuration that reduces the oxidation of formate (or the oxidation of other organic acid derivatives) without the need for a bipolar membrane. For example, a three-chamber electrochemical cell configuration can be provided with chambers separated by a cation exchange membrane. Such a configuration includes a central diluate chamber for receiving leachate and a concentrate chamber or catholyte (adjacent to the cathode) separated from the diluate chamber by a cation exchange membrane, which blocks multivalent transition metals and allows lithium ions to pass through the diluate chamber into the concentrate chamber to form lithium hydroxide in the concentrate chamber. This cell configuration further includes an anolyte chamber in contact with the anode, which is separated from the diluate chamber adjacent to the anolyte chamber by a cation exchange membrane. The cation exchange membrane between the electrolyte (e.g., lithium sulfate / sulfuric acid solution) in the anolyte chamber and the lithium formate solution in the central diluate chamber and the anode helps to block the diffusion of formate ions and formic acid, thereby reducing the oxidation of formate at the anode.

[0018] In the three-chamber configuration described above, crossover of organic acids (e.g., formic acid) into the anolyte and catholyte still exists. This can be mitigated by choosing a membrane that is more resistant to organic acid (e.g., formic acid) crossover. Alternatively, if the organic acid is deprotonated (i.e., the pH is adjusted / maintained above the pKa of the organic acid), the organic acid cannot pass through the cation exchange membrane. Crossover of organic acids from the diluent to the catholyte of the electrochemical cell can be further reduced by forcing the organic acid to pass through a high pH solution such that the organic acid dissociates and cannot permeate the cation exchange membrane in contact with the catholyte. Thus, the electrochemical cell may further comprise a neutralization chamber located between the diluent and concentrate chambers, the neutralization chamber being maintained at a pH above 4, 5, or 6, and / or the neutralization chamber being maintained at a pH above the pKa of the organic acid.

[0019] The methods described herein can be applied to materials that contain, in addition to Li, one or more of nickel, manganese, and cobalt, e.g., lithium-ion battery scrap materials such as black nuggets. [Brief description of the drawings]

[0020] [Figure 1] An example of a recycling process for battery materials is shown below. [Diagram 2] 1 shows another example of a recycling process for battery materials. [Diagram 3] (a) and (b) show process flow diagrams of the lithium extraction process producing delithiated black mass and lithium hydroxide, and (b) shows that the lithium hydroxide can be reintroduced into a new cathode synthesis process to recycle lithium from spent cathodes to produce new cathodes for lithium batteries. [Figure 4] Figure 1 shows leaching results using 98% formic acid as the leaching medium with NMC-111 as the input material, the image on the left shows the selectivity of the leaching medium and the image on the right shows the efficiency of the leaching medium. [Diagram 5] Leaching results using 98% formic acid as leaching medium and (NH4)2SO4 as additive for NMC-111 as input material are shown, the image on the left shows the selectivity of the leaching medium and the image on the right shows the efficiency of the leaching medium. [Figure 6] Figure 1 shows leaching results using an azeotropic mixture of 77.5 wt% formic acid and 22.5 wt% water as the leaching medium with NMC-111 as the input material, the image on the left shows the selectivity of the leaching medium and the image on the right shows the efficiency of the leaching medium. [Figure 7] The results of leaching using an azeotropic mixture of 77.5 wt% formic acid and 22.5 wt% water as the leaching medium with NMC-111 as the input material and (NH4)2SO4 as the additive are shown. The image on the left shows the selectivity of the leaching medium and the image on the right shows the efficiency of the leaching medium. [Figure 8]Figure 1 shows leaching results using a solution of 50 wt% formic acid, 45 wt% water and 5 wt% H2O2 as the leaching medium with eLNO as the input material, the image on the left shows the selectivity of the leaching medium and the image on the right shows the efficiency of the leaching medium. [Figure 9] FIG. 1 shows an electrochemical cell configuration for electrolyzing lithium formate leachate to produce lithium hydroxide, the electrochemical cell configuration including a two-chamber repeat unit (repeating unit indicated in the figure by “…”) between the anode / anolyte and cathode / catholyte, the system configured to selectively separate the lithium hydroxide product from transition metals in the leachate while limiting formate oxidation and allowing for the recovery and recycle of high levels of formic acid. [Figure 10] FIG. 10 shows an example of an electrochemical cell configuration. [Figure 11] FIG. 11 shows an expanded version of the electrochemical cell configuration shown in FIG. 10, including three of the two-chamber repeat units between the anode / anolyte and cathode / catholyte. [Figure 12] FIG. 9 shows the results of a cell configuration showing a decrease in lithium concentration in the diluent over time and an increase in lithium concentration in the concentrate over time, where 25% formic acid was used as the anolyte and catholyte, bipolar membranes were placed on either side of a cation exchange membrane to form a diluent chamber and a concentrate chamber, and the formic acid concentration in the diluent was 40%. [Figure 13] The results are shown for the same cell setup as in Figure 12, which shows selected elements in a four-chamber experiment, and it is also clear that the central cation exchange membrane (e.g., Nafion 424) is monovalent selective under these conditions, and that the bipolar membrane prevents metals from entering the anolyte and catholyte (although small amounts of sodium pass through). [Figure 14]Showing a cation exchange membrane loaded with polyvalent metals (left) and the same membrane after stripping with 8M H2SO4 (right), we demonstrate that this system can be used to selectively extract Li over polyvalent transition metals, and that the membrane can be regenerated by chemical stripping (or by periodic cell current reversal). [Figure 15] The solubility of lithium formate and lithium hydroxide versus temperature is shown, and it is shown that lithium hydroxide can be selectively precipitated at elevated temperatures from a mixture of lithium hydroxide and lithium formate produced by electrolysis of the lithium formate leach solution. [Figure 16] An example of a flow diagram of the overall process for electrolysis of lithium formate to produce lithium hydroxide is shown, including recycling of formic acid through leaching and electrolysis processes, selective precipitation and washing of the lithium hydroxide product obtained from the electrolysis process, and recycling of the supernatant and washing solutions from the precipitation / washing process to the electrolysis process, thereby providing an economically and ecologically viable system through efficient use of reagents. [Figure 17] An example of a three-chamber electrolysis system capable of electrolyzing a lithium formate-containing solution to produce formic acid and lithium hydroxide is shown, which is configured to selectively separate the lithium hydroxide product from transition metals in the leachate while limiting the oxidation of formate and allowing for the recovery and recycle of high levels of formic acid. [Figure 18] Figure 2 shows the change in lithium concentration over time in the catholyte and anolyte using a three-chamber electrolysis system. [Figure 19] FIG. 1 shows the change in lithium concentration over time in the anolyte, diluent and catholyte (in this case the "concentrate") using a three-chamber electrolysis system. [Figure 20] 4 shows the concentrations of other selected elements over time in the anolyte, diluent and catholyte using a three-chamber electrolysis system. [Figure 21]4 shows the pH of the catholyte and anolyte versus time using a three-chamber electrolysis system. [Figure 22] 1 shows the concentration of formate in the anolyte and catholyte versus time using a three-chamber electrolysis system (which may be determined, for example, by analysis of carbon concentration by ICP). [Diagram 23] A comparison of the change in catholyte lithium concentration in a three-chamber electrolysis system when starting with a lower lithium concentration in the diluent (AI3822) versus a higher lithium concentration in the diluent (AI3816) is shown, with the results indicating that enrichment of lithium in the catholyte is much more rapid in the instance where the starting lithium concentration in the diluent is higher, thereby providing a favorable concentration gradient and equating to a higher current efficiency. [Figure 24] A comparison of the cell voltages of experiment AI3816 and experiment AI3822 using a three-chamber electrolysis system is shown, and the results show that, taking into account the cell voltage and current efficiency, the energy consumption intensity for producing lithium hydroxide from lithium formate is 8.1 kWh kg-1 for AI3816 and 16.1 kWh kg-1 for AI3822. [Diagram 25] An example of a three-chamber electrolysis system similar to that shown in FIG. 17 is shown. [Figure 26] An example of an improved version of the configuration of FIG. 25 is shown, which provides a four-chamber electrolysis system in which the formic acid supply chamber is separated from the LiOH product chamber by a "neutralization chamber" to further reduce formate crossover and formate oxidation. [Figure 27]Formic acid crossover results are presented for two different types of membranes, Nafion115 and Nafion424, and the results show that by switching from a Nafion115 membrane (127 micrometers thick) to a Nafion424 membrane (380 micrometers thick), the formic acid crossover was reduced by 62% (in these experiments, the membrane behavior was investigated with no current flowing through the cell). [Figure 28] Water crossover results are presented for two different types of membranes, Nafion115 and Nafion424, and the results show that by switching from a Nafion115 membrane (127 micrometers thick) to a Nafion424 membrane (380 micrometers thick), water crossover was reduced by 69% (in these experiments, the membrane behavior was investigated with no current flowing through the cell). [Figure 29] The effect of formic acid concentration on formic acid crossover is shown, i.e., with increasing concentration, the formic acid crossover rate increases, plateaus, and then decreases, indicating that decreasing or increasing the formic acid concentration can reduce formic acid crossover. [Diagram 30] Figure 1 shows the crossover rate of formate / formic acid under different neutralization chamber solution pH (note that these experiments were performed without current flow and that at low pH, formic acid is protonated, whereas as the pH increases closer to 3.75, the crossover decreases as formic acid becomes deprotonated and no longer passes through the cation exchange membrane). [Diagram 31] Compared to the comparative two-chamber test configuration, the use of a four-chamber configuration including a neutralization chamber shows that crossover of formic acid into the catholyte (LiOH) was essentially eliminated (first three columns). [Diagram 32] FIG. 13 illustrates yet another example of an electrolysis system, the cell configuration being similar to that shown in FIGS. 9-11 except that it has a "neutralization chamber" between the diluent and concentrate chambers to reduce formic acid crossover and oxidation of formic acid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] As described in the Overview section, the present specification provides a method for recycling Li from an input material containing Li and one or more transition metals, the method comprising: contacting the input material with a leaching medium comprising an organic acid (e.g., formic acid); Leaching Li from the input material to form a leachate comprising an organic lithium salt (e.g., lithium formate); and b. electrolytically converting an organic lithium salt (e.g., lithium formate) to an inorganic lithium salt (e.g., lithium hydroxide or lithium carbonate).

[0022] According to certain embodiments, the electrochemical processing methods and cell configurations used for the electrolytic conversion of lithium formate to lithium hydroxide include the use of one or more membranes that are selective for the permeation of monovalent lithium over the permeation of multivalent transition metals. In this case, such electrochemical cell configurations and methods are capable of both separating lithium from multivalent transition metal impurities in the leachate and converting lithium formate to lithium hydroxide. Alternatively, or in addition, a multivalent metal separation step (such as an ion exchange process) may be applied to the leachate prior to electrolysis. In this case, the use of selective membranes is not necessary in the electrochemical cell configuration, and only the conversion of lithium formate to lithium hydroxide is required.

[0023] The method may be applied to the recycling of a variety of functional input materials, but is particularly useful for the recycling of cathode materials in lithium-ion batteries. In this regard, FIG. 1 shows an example of a battery material recycling process. The starting material is cathode scrap, or so-called "black lump", which typically contains Li, Ni, Co, Mn, and impurities including Cu and Fe. This material is subjected to an acid dissolution or leaching step to obtain an acidic aqueous recycle feed containing the constituent metal species in solution. Impurities such as Cu and Fe can be removed by ion exchange or hydrolysis. An organic solvent extraction step can then be applied to separate Co and Ni (in the organic phase) from Mn and Li. An acid scrub can be further applied to the organic phase to remove impurities before stripping the Co and Ni into an aqueous Co and Ni solution. The organic phase can be regenerated and recycled for use in further extraction of Co and Ni. The method of FIG. 1 allows Co and Ni to be separated from the cathode black lump material. However, further process steps are required to separate Li and Mn from each other.

[0024] FIG. 2 shows another example of a battery material recycling process. Again, the starting material is cathode scrap, or so-called "black nugget," which typically contains Li, Ni, Co, Mn, and impurities including Cu and Fe. However, in this example, the lithium is first removed by treatment with a suitable solvent (e.g., an organic acid such as formic acid) that dissolves Li but not other metal species. The remaining material is subjected to an acid dissolution or leaching step to obtain an acidic aqueous recycle feed containing the remaining constituent metal species in solution. Impurities such as Cu and Fe can be removed by ion exchange or hydrolysis. An organic solvent extraction step can then be applied to separate Co and Ni (in the organic phase) from Mn. An acid scrub can be further applied to the organic phase to remove impurities before stripping the Co and Ni into an aqueous Co and Ni solution. The organic phase can be regenerated and recycled for use in further extraction of Co and Ni. The method of FIG. 2 is advantageous in that an efficient four-way separation of Li, Mn, Co, and Ni can be achieved.

[0025] The method herein can be applied to the battery material recycling process of FIG. 2, where lithium is removed from the black mass by leaching with formic acid. As previously described in the overview section, formic acid selective leaching of lithium from the black mass produces a concentrated aqueous formic acid solution containing mainly lithium with lower concentrations of other metals. For the lithium extraction approach to be economically and ecologically viable, the lithium formate in this solution needs to be converted to inorganic lithium salts (e.g., lithium hydroxide and lithium carbonate) for reuse in the lithium-ion battery cathode material synthesis, and the formic acid needs to be recycled for reuse in the formic acid leaching step of the recycling process. Such a method according to the present specification is shown in FIG. 3(a) and FIG. 3(b). While lithium carbonate can be electrochemically formed in the CO2 generation area (4Li + +4e -+O2+2CO2→2Li2CO3), it should be noted that the battery cathode material manufacturing industry is transitioning from using Li2CO3 to using LiOH, which will be the primary precursor. Thus, the examples herein will focus primarily on the formation of lithium hydroxide salts, while recognizing that other lithium salts may be formed using the teachings herein.

[0026] The following description includes a section detailing the formic acid leaching process described in the Patent Owner's previous UK Patent Application No. 2016329.1 (which is incorporated herein for completeness), followed by a section detailing several different methods for the electrochemical conversion of lithium formate to lithium hydroxide for reuse in the manufacture of new functional materials (e.g., lithium ion battery materials).

[0027] Formic Acid Leaching The formic acid leaching process comprises selectively removing Li from an input material containing Li and one or more transition metals, the formic acid leaching process comprising: contacting the input material with a leach medium comprising formic acid and leaching Li from the input material to form a leachate; The concentration of formic acid in the leaching medium is at least 40% by weight.

[0028] As previously mentioned, the input material is typically battery scrap, particularly cathode scrap from lithium ion or solid-state lithium batteries. The battery scrap may have been previously used in an electrical energy storage device, but this is not required. The battery scrap may be waste material generated during the manufacture of batteries or materials, including, for example, waste intermediate material or failed batches. In some embodiments, the battery scrap is formed by mechanical and / or chemical processing of waste lithium ion batteries.

[0029] In some embodiments, the input material includes lithium and one or more of iron, nickel, cobalt, and manganese. In some embodiments, the input material includes lithium, nickel, and cobalt. In some embodiments, the input material includes lithium, nickel, cobalt, and manganese.

[0030] As will be appreciated by one of ordinary skill in the art, the input materials may further include other elements and / or materials from the electrochemical storage device, such as the cathode material, current collector, anode material, electrolyte and other elements from any battery or cell casing.

[0031] In preferred embodiments, the material includes one or more of nickel, manganese, and cobalt in addition to Li. In some embodiments, the material includes each of nickel, manganese, and cobalt in addition to Li.

[0032] The input material can include at least 10 wt.%, e.g., at least 12 wt.%, at least 15 wt.%, at least 20 wt.%, or at least 25 wt.% Ni based on the total mass of the input material. The input material can include up to 80 wt.%, e.g., up to 75 wt.%, up to 70 wt.%, or up to 50 wt.% Ni based on the total mass of the input material. The input material can include 10-80 wt.% Ni based on the total mass of the input material.

[0033] The input material can include at least 0 wt.%, e.g., at least 1 wt.%, at least 2 wt.%, at least 5 wt.%, or at least 10 wt.% Mn based on the total mass of the input material. The input material can include up to 33 wt.%, e.g., up to 30 wt.%, up to 28 wt.%, or up to 25 wt.% Mn based on the total mass of the input material. The input material can include 0-33 wt.% Mn based on the total mass of the input material.

[0034] The input material can include at least 0 wt%, e.g., at least 1 wt%, at least 2 wt%, at least 5 wt%, or at least 10 wt% Co based on the total mass of the input material. The input material can include up to 33 wt%, e.g., up to 30 wt%, up to 28 wt%, or up to 25 wt% Co based on the total mass of the input material. The input material can include 0-33 wt% Co based on the total mass of the input material.

[0035] The input material can include at least 0 wt.%, e.g., at least 1 wt.%, at least 2 wt.%, at least 5 wt.%, or at least 6 wt.% Li based on the total mass of the input material. The input material can include up to 20 wt.%, e.g., up to 18 wt.%, up to 15 wt.%, or up to 12 wt.% Li based on the total mass of the input material. The input material can include 0-20 wt.% Li based on the total mass of the input material.

[0036] The input material can include at least 0 wt.%, e.g., at least 1 wt.%, at least 2 wt.%, or at least 3 wt.% Fe based on the total weight of the input material. The input material can include up to 10 wt.%, e.g., up to 9 wt.%, up to 8 wt.%, or up to 7 wt.% Fe based on the total weight of the input material. The input material can include 0-10 wt.% Fe based on the total weight of the input material.

[0037] The input material can include at least 0 wt.%, e.g., at least 1 wt.%, at least 2 wt.%, or at least 3 wt.% Al based on the total mass of the input material. The input material can include up to 10 wt.%, e.g., up to 9 wt.%, up to 8 wt.%, or up to 7 wt.% Al based on the total mass of the input material. The input material can include 0-10 wt.% Al based on the total mass of the input material.

[0038] The input material can include at least 0 wt.%, e.g., at least 1 wt.%, at least 2 wt.%, or at least 3 wt.% Cu based on the total mass of the input material. The input material can include up to 20 wt.%, e.g., up to 15 wt.%, up to 10 wt.%, up to 9 wt.%, up to 8 wt.%, or up to 7 wt.% Cu based on the total mass of the input material. The input material can include 0-20 wt.% Cu based on the total mass of the input material.

[0039] The input material can comprise at least 0 wt.%, e.g., at least 1 wt.%, at least 5 wt.%, at least 10 wt.%, or at least 15 wt.%, C based on the total mass of the input material. The input material can comprise up to 50 wt.%, e.g., up to 45 wt.%, up to 40 wt.%, or up to 30 wt.%, C based on the total mass of the input material. The input material can comprise 0-50 wt.% C based on the total mass of the input material.

[0040] The input material may include 10-80 wt% Ni, 0-33 wt% Mn, 0-33 wt% Co, 0-20 wt% Li, 0-10 wt% Fe, 0-10 wt% Al, 0-10 wt% Cu, and 0-50 wt% C, based on the total mass of the input material.

[0041] Two important parameters to consider in the leaching process are leaching efficiency and leaching selectivity. Leaching efficiency is the fraction of a given metal in the input material that is leached by the leaching medium. For example, if the input material contains 10 g Li and after leaching 9 g Li is leached, the leaching efficiency of Li is 90%.

[0042] Leaching selectivity refers to the percentage of a given metal leached relative to the total metals leached. In the figure below, leaching selectivity is plotted based on the total molar content of metal ions in the leaching medium. For example, if after leaching the medium contains 0.95 moles Li and 0.05 moles Ni (1.0 mole total metals), then the leaching selectivity for Li is 95%. Leaching selectivity is sometimes reported based on the total weight percent of metals leached, but the low mass of Li compared to the other metals can obscure the selectivity.

[0043] The process uses a leaching medium that includes a formic acid concentration of at least 40 wt. %. Although the highest selectivity for Li removal is achieved by using essentially pure formic acid (98% or more formic acid, see the examples) and / or by using high temperatures, in some embodiments it may be preferred to use a leaching medium that is relatively dilute formic acid (e.g., at least 40% formic acid with up to 60% water or at least 50% formic acid with up to 50% water). Although such solutions are not as selective for Li removal as 98% or more formic acid, their use poses less of an engineering challenge compared to higher concentrations of formic acid, which require more expensive plant equipment. The use of a leaching medium that is relatively dilute formic acid may also be preferred from a safety standpoint, since it is less flammable compared to concentrated formic acid. Manganese salts have been shown to be particularly detrimental to Li leaching selectivity due to their high solubility in aqueous formic acid solutions. Thus, the use of a leaching medium that is relatively dilute formic acid may be particularly acceptable when the substrate is substantially manganese-free.

[0044] Typically, the leaching medium comprises a concentration of formic acid of at least 70 wt%. The inventors have found that such a leaching medium has a high leaching selectivity for Li. In a preferred embodiment, the concentration of formic acid in the leaching medium is at least 80 wt%. In a preferred embodiment, the concentration of formic acid in the leaching medium is at least 90 wt%, such as at least 98 wt% or at least 99 wt%. In general, the higher the concentration of formic acid in the leaching medium, the higher the leaching selectivity for Li. A leaching medium that is substantially pure formic acid has the advantage of a higher removal efficiency and higher selectivity for Li over other transition metals, particularly Ni, Mn, and Co.

[0045] In some embodiments, the leaching medium is an azeotrope of formic acid and water, comprising 77.5% by weight formic acid and 22.5% by weight water. As will be understood by those skilled in the art, the azeotrope boils without changing the ratio of formic acid to water. This allows the leaching medium to be recycled more directly, for example, by evaporating the solvent off of the leachate. Since formic acid is consumed during the leaching process (e.g., through the production of lithium formate), the recycle loop usually includes a step of ensuring that the composition of the azeotrope is maintained in the reactor, for example, by adding fresh leaching medium having a higher formic acid concentration than that in the azeotrope.

[0046] In some embodiments, the leaching medium comprises H2O2. In addition to formic acid, H2O2 serves to reduce transition metals in the input material (e.g., from +3 or +4 oxidation states to +2 oxidation states). If present in the leaching medium, the concentration of H2O2 in the leaching medium is preferably in the range of 1-10 wt%, more preferably 3-7 wt%. From a safety standpoint, lower concentrations of H2O2 are desirable.

[0047] In some embodiments, leaching can be performed while agitating the substrate, for example using stirring or ultrasound, to ensure efficient contact between the leaching medium and the input materials.

[0048] It is generally established that the higher the temperature during the leaching process, the higher the leaching efficiency and leaching selectivity. Preferably, the mixture of leaching medium and input material is heated to a temperature of at least 40° C. during the leaching process. Typically, to achieve high leaching efficiency, the temperature during the leaching process will be at least 60° C. Preferably, the temperature during the leaching process will be at least 80° C., and in some embodiments at least 90° C. In some embodiments, the mixture is heated to above the boiling point of the leaching medium, for example under reflux.

[0049] The duration of heating must be sufficient to remove substantially all of the Li from the input material. This may depend in part on the temperature of the leaching medium, and the physical form and chemical properties of the input material. An unnecessarily long duration is disadvantageous from a cost standpoint. Suitable durations will be readily ascertainable by those skilled in the art. When leaching is carried out as a batch process, typical heating durations are 5-120 minutes, preferably 5-60 minutes.

[0050] The input material is typically contacted with the leaching medium at room temperature or above and then heated to the desired temperature. In some embodiments, the leaching medium may be preheated before contacting the input material without further heating the mixture. Alternatively, the leaching medium may be at ambient temperature when contacted with the input material, and the mixture is then heated to the desired temperature. It is also possible to preheat the leaching medium before contacting the input material, and then further heat the mixture to the desired temperature.

[0051] An important parameter in the leaching process is the ratio of solid input material to leaching medium, called S / L. During the leaching process, metals are dissolved in the leaching medium as metal formates, of which lithium formate is the most soluble. The formation of metal formates is also accompanied by the production of water that dilutes the leaching medium (e.g. when the substrate is a metal oxide).

[0052] The use of a high S / L ratio is advantageous for a variety of reasons, including the need for a smaller volume of leaching medium, i.e., lower raw material costs, lower plant operating costs, and less waste volume. When the S / L ratio is high, the resulting leachate has a high concentration of lithium formate, which helps to suppress the dissolution of metal formates with lower solubility (e.g., Mn, Ni, or Co). On the other hand, when the S / L ratio is high, the leaching medium is easily diluted by water formed as a by-product of the leaching process, which is detrimental to leaching selectivity. In general, the S / L ratio is preferably at least 10 g / L, preferably at least 20 g / L, more preferably at least 30 g / L. Typical ranges of S / L values ​​are 10-150 g / L, e.g., 20-150 g / L, 30-150 g / L.

[0053] In some embodiments, additives can be added to the leaching medium to further prevent leaching of transition metals in the input material, thereby improving leaching selectivity for Li. The use of additives may be particularly appropriate when the S / L ratio is high and / or when the leaching medium has a relatively low concentration of formic acid. The nature of the salt is not particularly important, so long as it has high solubility in the leaching medium and does not impede the leaching of Li or disrupt downstream steps. A preferred type of salt is sulfate, which has been discovered by the inventors to prevent the leaching of transition metals, particularly Mn. The nature of the counter ion in the sulfate is not particularly important, although it is preferred that the counter ion is non-metallic to avoid unnecessary contamination of the leaching medium with additional metals. A preferred additive is ammonium sulfate. The additive can be added to the leaching medium either before or after contact with the input material. Typically, the additive is added to the leaching medium in an amount of 10 to 100 g / L, for example 20 to 80 g / L or 20 to 50 g / L, these values ​​being particularly suitable in the case of ammonium sulfate.

[0054] The process described herein provides for the selective leaching of Li from the input material. Without wishing to be bound by theory, it is believed that initially the formic acid (and H2O2, if present) reduces metal ions in the input material, allowing the Li-ions to dissolve in the leaching medium. The resulting output material is a transition metal oxide. Over time, it is believed that this reacts with excess formic acid to produce the corresponding metal formate and water. The metal formate remains solid due to its low solubility in the leaching medium.

[0055] Example of formic acid leaching material NMC111 - Supplier Targray. Formic Acid - 98% Grade Fisher Scientific. Ammonium Sulfate - Supplied by Acros Organics. Lithium nickel cobalt oxide cathode material available from Johnson Matthey Plc under the trade name eLNO™.

[0056] Example 1 (98% by weight formic acid + NMC 111) 2 g of NMC 111 was added to 50 mL of formic acid in a 100 mL round bottom flask equipped with a condenser. The solution was heated to boiling (approximately 103° C.) while the suspension was stirred at 500 rpm, which typically required a heating plate set at 130° C. After 1 hour, the solution was filtered and the leachate was analyzed for elemental analysis using ICP-OES.

[0057] Figure 4 shows that over 90% of Li was leached from NMC 111 within 1 h, with Li accounting for >90 wt% of the metal in the leachate. With increasing temperature, the leaching efficiency for Li increased, but there was no sign of a change in leaching selectivity. Under each condition, only a small amount of Mn dissolved in the leaching medium, which increased slightly with increasing temperature. Leaching of Co and Ni was negligible.

[0058] Example 2 (98% by weight formic acid + NMC 111 + (NH4)2SO4) The procedure of Example 1 was followed except that 2 g of (NH4)2SO4 was added to the leachate.

[0059] FIG. 5 shows that although the leaching efficiency is not as high as in Example 1, the leaching selectivity is higher than in Example 1 at temperatures above 60° C., and there is little leaching of Ni, Co, or Mn.

[0060] Example 3 (77.5 wt% formic acid / 22.5 wt% HO+NMC111) The procedure of Example 1 was followed, substituting 50 mL of an azeotrope of formic acid and water (77.5% formic acid and 22.5% H2O) instead of 50 mL of formic acid.

[0061] Figure 6 shows that when an azeotropic mixture of formic acid and water was used as the leaching medium, high leaching efficiency was still provided, although the leaching selectivity was not as high as when 98% formic acid was used. The leaching of Mn(II) ions was significant, especially with increasing temperature.

[0062] Example 4 (77.5 wt% formic acid / 22.5 wt% H2O+NMC111+(NH4)2SO4) The procedure of Example 3 was followed except that 2 g of (NH4)2SO4 was added to the leaching medium.

[0063] Figure 7 shows that inclusion of (NH4)2SO4 resulted in higher selectivity for Li and lower concentrations of undesirable metal ions in the leachate compared to the use of the formic acid-water azeotrope alone (Example 3), and in particular suppressed the dissolution of Mn.

[0064] Example 5 (50 wt% formic acid / 45 wt% H2O+5% H2O2+eLNO) The procedure of Example 1 was followed, except that the leaching medium was a mixture of 50 wt% formic acid, 45 wt% water, and 5 wt% H2O2, and 2 g of lithium nickel cobalt oxide cathode material was used instead of 2 g of NMC 111.

[0065] FIG. 8 shows that high efficiency and relatively high selectivity for Li can be achieved using dilute performic acid as the leaching medium, although the leaching selectivity was not as high as in Examples 1-4, which used more concentrated leaching media.

[0066] Electrolysis of lithium formate to produce lithium hydroxide Selective leaching of lithium formate (e.g., from black mass) as described in the previous section produces a concentrated aqueous solution of formic acid containing mainly lithium with lower concentrations of other metals. For this lithium recycling approach to be economically and ecologically viable, the lithium formate in this solution needs to be converted to lithium hydroxide for lithium ion cathode material synthesis, and the formic acid needs to be recycled for reuse in leaching. Although lithium sulfate can be electrolyzed to lithium hydroxide and sulfuric acid using a relatively standard two-chamber electrolyzer, the use of such an approach to electrolyze lithium formate to lithium hydroxide has been found to be suboptimal due to oxidation of the formate at the anode. Thus, improved electrochemical methods are desired to provide a more efficient and sustainable method of electrolyzing lithium formate to lithium hydroxide. Some of such improved approaches are described below.

[0067] Conversion of lithium formate to lithium hydroxide and formic acid by two-chamber bipolar membrane salt splitting electrolysis This approach provides an integrated process for converting lithium formate contained in the formic acid leachate of the black mass of lithium-ion batteries to solid lithium hydroxide, while regenerating formic acid for reuse in leaching. It is centered around a two-chamber salt splitting electrolysis that uses a bipolar membrane as the repeating unit in the cell stack, rather than electrodes on either side of a cation exchange membrane. The use of a bipolar membrane significantly reduces the rate of oxidation of formic acid, as the majority of protons formed in the electrolysis are generated by dissociation of water, rather than oxidation of water. The process also advantageously involves selectively precipitating lithium hydroxide from a mixed solution of hydroxide and formate. The method also advantageously uses a pH gradient across the cation exchange membrane to significantly reduce the flux of polyvalent elements from the formic acid leachate to LiOH, and a membrane stripping process in which these impurities are removed by flowing a >3M sulfuric acid solution through the cell. Alternatively, if a dedicated monovalent selective cation exchange membrane is used, the monovalent selectivity can be based on 2+ charge repulsion rather than a pH gradient.

[0068] The approach described in this section provides a two-chamber electrolysis system that allows for the electrolysis of lithium formate-containing solutions in a salt splitting electrolysis to produce formic acid and lithium hydroxide without significant oxidation of the formate to CO2 at the anode. The overall salt splitting reaction is: LiCHOO+1.5H2O-->LiOH+HCHOO+(1 / 4O2(g)+1 / 2H2(g))

[0069] The reaction is induced by applying an electric current between the anode and cathode of the cell. The applied current may be constant or may be varied during operation to control the reaction. Note also that the gas stoichiometry shown in the equation is correct for the case where no bipolar membrane is used, the faradaic efficiency is 100%, and changes when such a bipolar membrane is used.

[0070] A diagram of the cell configuration is shown in FIG. 9. This configuration includes two chambers 1, 2. The two chambers 1, 2 are repeated in the stack between the anode and the cathode as indicated by "..." in FIG. 9. The two chambers 1, 2 are separated by a cation exchange membrane (CEM) at the cathode side of chamber 1 and a bipolar membrane (BPM) at the anode side of chamber 1. A formic acid leachate containing lithium formate is pumped through chamber 1. The lithium cations in chamber 1 pass through the cation exchange membrane and enter chamber 2 at the cathode side of chamber 1, where they combine with hydroxide anions formed by dissociation of water at the bipolar membrane to form lithium hydroxide. The hydroxide anions in chamber 1 are formed at the bipolar membrane and migrate through the bipolar membrane towards the anode at the anode side of chamber 1, while protons are formed at the bipolar membrane and pass through the bipolar membrane to enter chamber 1 at the anode side of chamber 1.

[0071] FIG. 10 shows an example of the electrochemical cell configuration shown in FIG. 9. In the example of FIG. 10, the anode is an iridium oxide-based anode and the cathode is a platinum-based cathode, but it is noted that other anode and cathode materials can be utilized. 77% of the formic acid leachate is shown to be pumped into chamber 1 (diluate) and lithium hydroxide is formed in chamber 2 (concentrate). Again, the two chambers 1, 2 are repeated in the stack between the anode and cathode, as indicated by "...". In the example shown in FIG. 10, 25% of the formic acid is pumped through the anolyte chamber adjacent to the anode and 25% of the formic acid is also pumped through the catholyte chamber adjacent to the cathode. However, the anolyte and catholyte, i.e., the electrolyte that is actually in direct contact with the anode and cathode, may actually be the same lithium hydroxide solution circulating in the "concentrate" chamber. Indeed, the electrolyte which is in direct contact with the anode and cathode may be any conductive electrolyte for which it is not problematic for components to pass through the bipolar membrane and into the LiOH or leachate stream.

[0072] The full-scale cell configuration is a "stack" in which several repeat units are placed adjacent to each other between the anode and cathode. The repeat unit consists of a cation exchange membrane between two bipolar membranes. Figure 11 shows an enlarged version of the electrochemical cell configuration shown in Figure 10 to clarify the repeat structure. In a two-chamber repeat unit, the lithium formate-containing solution can be circulated through the chamber closest to the anode, and the LiOH solution can be recirculated through the chamber on the other side of the cation exchange membrane closest to the cathode. Note, however, that the beneficial formate salt must be stored away from the anode portion of the cell where it can be oxidized and lost.

[0073] At the anode, the anode water decomposition reaction (H2O-->1 / 2O2+2H + +2e - ) produces protons, and at the cathode, hydroxide ions are produced by the decomposition of water at the cathode (H2O+2e - -->2OH - +1 / 2H2(g).

[0074] The bipolar membrane splits water (on each side of the adjacent anion and cation exchange layers of the bipolar membrane) without producing gas by dissociation of water: HO-->H + +OH - .

[0075] There can be 2, 4, 6, 8, 10, 15, 20 or more two-chamber repeat units in the stack between the anode and cathode electrodes. Thus, the majority of the protons and hydroxide ions are formed at the bipolar membrane rather than at the electrodes. By generating protons primarily through dissociation rather than oxidation of water, the rate of oxidation of formic acid is greatly reduced. If all protons were generated at the anode, formic acid in contact with the anode would be preferentially oxidized over water.

[0076] When a current is applied to the cell, Li +The ions and protons pass through the cation exchange membrane into the LiOH electrolyte. + The charge of the ions is transferred to the newly generated OH - The charge of the ions balances the charge. + The ions leave formate anions on the other side of the membrane, and their charge is balanced by protons produced by the other bipolar membrane. In this way, formic acid is regenerated as LiOH is produced. Alternatively, Li + The ions migrate to the cathode compartment, where they are converted by the bipolar membrane into OH - ions, whereas formate anions react with H + and reacts.

[0077] In the lithium formate-containing solution, Cu 2+ or Mn 2+ However, the pH gradient across the cation exchange membrane (the formate side is acidic, the LiOH side is basic) + This means that at high pH, ​​the polyvalent metals are too strongly bound to the anionic (e.g., sulfonate) functional groups of the cation exchange membrane to migrate, whereas lithium is not as strongly bound and can migrate. This means that after a while the cation exchange membrane can become blocked with polyvalent metals and must be stripped, for example, by flowing sulfuric acid (e.g., greater than 2 molar) through the cell.

[0078] Figure 12 shows the results for the four-chamber cell configuration of Figure 9, where the results show that the lithium concentration in the diluent decreases and the lithium concentration in the concentrate increases over time, in a cell configuration where 25% formic acid is used as the anolyte and catholyte, and bipolar membranes are provided on either side of the cation exchange membrane to form the diluent and concentrate chambers between the anolyte and catholyte. In this experiment, the formic acid concentration in the diluent was 40%. Figure 13 shows the results for the same cell configuration as Figure 12, where the results show the selected elements in the four-chamber experiment, and the central cation exchange membrane (e.g. Nafion 424) is monovalent selective under these conditions. It is also clear that the bipolar membrane prevents the entry of metals into the anolyte and catholyte (although a small amount of sodium does pass through).

[0079] To illustrate the stripping process, Figure 14 shows a Nafion N115 cation exchange membrane loaded with polyvalent metals (left) and the same membrane after being stripped with 8 M H2SO4 (right). As an alternative to chemical stripping, it is also possible to remove polyvalent metal impurities that have accumulated in the membrane components by periodically reversing the cell current, although care must be taken to avoid delamination of the bipolar membrane when using this approach.

[0080] Formic acid (especially at high concentrations) can pass through both the cation exchange membrane and the bipolar membrane as associated neutral molecules. As formic acid migrates across the membrane from the lithium formate-containing electrolyte to the LiOH electrolyte, it reacts with LiOH to form lithium formate. Because LiOH is the desired product, lithium hydroxide must be separated from the lithium formate.

[0081] Lithium hydroxide and lithium formate can be separated by selectively precipitating LiOH at high temperatures (i.e., by boiling the solution or precipitating by other evaporative methods at temperatures above 80° C.). Figure 15 shows the solubility of lithium formate and lithium hydroxide versus temperature. At 100° C., lithium formate is 3.6 times more soluble than lithium hydroxide, indicating that precipitation is selective with high recovery of LiOH from solution, i.e., selective precipitation of hydroxide from formate mixtures is possible.

[0082] The LiOH precipitate can then be washed with saturated hot LiOH solution to remove any remaining formate. The formate-containing supernatant and wash solution can then be recycled back to the LiOH-containing chamber of the cell. However, there is also a bleed of the supernatant provided from the precipitation into the formate-containing chamber of the cell. Its purpose is to provide an outlet for formate that would otherwise accumulate in the LiOH stream, and also to allow "crossed-over" formate to be regenerated to formic acid.

[0083] Figure 16 shows an example of a flow diagram of the entire process of electrolysis of lithium formate to produce lithium hydroxide, including recirculation of the formic acid through the leaching process, and precipitation and washing of the lithium hydroxide product, including recirculation of the supernatant and washings. The process is designed for the context of recovering lithium as LiOH from the formic acid leachate of the "black mass" of lithium-ion batteries. Regenerating the formic acid used in the leaching can significantly reduce the amount of formic acid consumed in the process and the amount of waste produced. The advantage of using bipolar membranes is that the rate of oxidation of the formic acid is significantly reduced, meaning that less CO2 is produced directly by the oxidation. Assuming that the power supplied to the electrolysis is renewable, the climate impact of the plant is improved when regenerating the formic acid in the electrolysis. Bipolar membranes also allow protons and hydroxide to be produced without the use of hydrogen and oxygen gases, so their use typically reduces the energy consumption of the process. Significantly reducing the rate of hydrogen production also has obvious benefits for environmental health and safety. Furthermore, an advantage of incorporating selective precipitation into electrolysis is that formate that passes through the cation exchange membrane and the bipolar membrane can be separated from the LiOH produced, while the "crossover" formate can be regenerated to formic acid.

[0084] A typical diluent feed treated using this method contains one, more or all of the following: Mn, Cu, Fe, Al, Zn, Mg, Na, Ni, Co. -1 Elements in the diluent feed less than 2 gL may include Mn and / or Cu. -1 Elements in the diluent feed less than 10000000000 may include Fe, Al, Zn, Mg, Na, Ni, and / or Co.

[0085] Typical operating conditions include one or more of the following:

[0086] Input formic acid concentration: 10 vol%, 20 vol%, 30 vol%, 40 vol%, 45 vol%, 50 vol%, 95 vol%, 90 vol%, 85 vol%, 80 vol% or less, or within a range defined by any combination of the above lower and upper limits. For example, within a range of 50 vol% to 85 vol%, for example, 70 vol%.

[0087] Input Li concentration (dilution): at least 0.5, 1, 2.5, 5, or 10 gL -1 Li + , 90, 70, 50, 40, 35, 25, or 20gL -1 The following Li + or within a range defined by any combination of the lower and upper limits set forth above. For example, 2.5 gL -1 Li + ~35gL -1 Li + Within the range of, for example, 12.5 gL -1 Li + .

[0088] Anolyte / catholyte formic acid concentration: at least 0 vol%, 2 vol%, 5 vol%, 10 vol%, 15 vol%, or 20 vol%, 80 vol%, 50 vol%, 35 vol%, or 30 vol% or less, or within a range defined by any combination of the aforementioned lower and upper limits, e.g., within the range of 10 vol% to 50 vol%, e.g., 25 vol%.

[0089] Output LiOH concentration: at least 2, 4, 6, 8, or 10 gL -1 Li + 40, 30, 20, or 15 gL -1 The following Li + or within a range defined by any combination of the lower and upper limits set forth above. For example, 10 gL -1 Li + ~35gL -1 Li + Within the range of, for example, 10 gL -1 Li + .

[0090] Current density: at least 10, 20, 30, or 40 mA cm -2 , 1000, 500, 400, 300, 200, or 100mA cm -2 or less; or within a range defined by any combination of the preceding lower and upper limits. For example, 10 mA cm -2 ~1000mA cm -2 is within the range.

[0091] In the experiments supporting this specification, the cell was charged to 13.5 V and 0.3 L / min -1 The system was operated at an electrolyte flow rate of 0.01 µm and an electrolyte volume of 0.27 L.

[0092] A three-chamber electrolysis capable of electrolyzing lithium formate-containing solutions to produce formic acid and lithium hydroxide without significant oxidation of the formate to CO2 In this approach, a three-chamber electrolysis is provided that can electrolyze a lithium formate-containing solution to produce formic acid and lithium hydroxide without significant oxidation of the formate to CO2. The lithium formate solution is decomposed into lithium hydroxide and formic acid. While a current is applied to the cell, the lithium formate solution circulates through the central chamber. Lithium ions pass from the central chamber through the cation exchange membrane to the cathode chamber to form lithium hydroxide. Protons, which are electrochemically generated by the decomposition of water at the anode, diffuse through the lithium sulfate / sulfuric acid solution and pass from the anode chamber through the cation exchange membrane to the central chamber where they balance the charge of the formate ions remaining in solution to form formic acid. The use of the cation exchange membrane and the lithium sulfate / sulfuric acid solution as the electrolyte between the lithium formate solution and the anode blocks the diffusion of formate ions and formic acid, reducing the oxidation of the formate at the anode.

[0093] This approach offers an alternative to the methods described in the previous section for recovering selectively leached lithium from the black mass of lithium-ion batteries. In particular, this lithium is recovered in the form of lithium hydroxide, which can be used as a precursor for the synthesis of cathode materials in lithium-ion batteries and can be easily converted to lithium carbonate (another major lithium precursor) by reaction with CO2. As with the previous approach, in this method formic acid can be regenerated without significant loss of formate by oxidation at the anode. This means that formic acid can be recycled for reuse in the selective leaching step.

[0094] One advantage of this approach is that it uses durable cation exchange membranes and does not require the use of bipolar membranes. Another advantage is that it can provide a lithium purification process when impure lithium formate containing multivalent metals is fed to the central chamber. Yet another advantage of this method is that the cell setup is well coordinated with the leaching step. In cells using anion exchange membranes, the regenerated formic acid is recovered in a different solution than the input stream, which can result in a significant volume of lithium-depleted solution as a waste stream. In this method, the acid is recovered in the initial input solution, allowing an equal volume of solution to be recycled to the leaching, and there is no waste stream. Note that this advantage also applies to the previous two-chamber cell configurations discussed herein.

[0095] FIG. 17 shows an example of a three-chamber electrolysis system, in which a lithium formate-containing solution can be electrolyzed in a salt splitting electrolysis at the anode to produce formic acid and lithium hydroxide without significant oxidation of the formate to CO2. The overall salt splitting reaction is LiCHOO+1.5H2O-->LiOH+HCHOO+1 / 4O2(g)+1 / 2H2(g). The reaction is triggered by applying a constant current between the anode and cathode of the cell (however, the current can be periodically and momentarily reversed to remove impurities from one of the cation exchange membranes). The lithium formate-containing solution is recirculated through the central chamber between the two cation exchange membranes, thereby selectively blocking the transport of formate anions but not Li. + Or H + The electrolyte in the central chamber is called the "diluent."

[0096] To a lesser extent, the cation exchange membrane also blocks the transport of neutral associated formic acid molecules from the central chamber. The lithium sulfate and / or sulfuric acid solution is recirculated through the anode chamber, which is separated from the central chamber by a cation exchange membrane. The electrolyte in the anode chamber is called the "anolyte".

[0097] If a two-chamber electrolysis cell is used and the lithium formate solution is recirculated through the anode chamber, formic acid cannot be produced efficiently because the formate ions are oxidized to CO2 at the anode. However, in a three-chamber setup, the cation exchange membrane acts as a barrier. Thus, the purpose of the anolyte is to inhibit the anodic water splitting reaction (H2O(l) --> 2H + (aq) + 1 / 2O2(g) + 2e - ) migrates from the anode to the cation exchange membrane, passing through the membrane into the diluent, providing an electrically conductive, electrochemically stable electrolyte.

[0098] Recirculating through the cathode chamber is the catholyte, a LiOH solution. The current applied to the cell is + Ions are driven from the diluent through a cation exchange membrane to initiate the water splitting reaction (2H2O(l) + 2e - -->2OH - (aq) + H2(g) - The charge of the ions is balanced, thereby forming LiOH.

[0099] As with the two-chamber cell configuration described above, the process can be run in batch or continuous flow mode, with the continuous flow mode being preferred for both cell configurations. In continuous flow mode, fresh lithium formate-containing solution flows into the recirculating diluent, and lithium-depleted, acidified diluent flows out, such that the total volume, acidity, and lithium concentration remain constant (i.e., steady-state operation). Similarly, water (or supernatant and wash solutions as shown in FIG. 16) is flowed into the catholyte at a rate that keeps the lithium concentration constant, and electrolyte is injected at a rate that maintains the total volume of the catholyte.

[0100] It has been found experimentally that the use of sulfonic acid cation exchange membranes selectively blocks polyvalent metals present in the diluent from passing through the membrane into the catholyte and anolyte compared to lithium. The selectivity is enhanced by the pH gradient across the membrane from the diluent to the anolyte, which causes the polyvalent metals to "stick" to the membrane due to their stronger interaction with the sulfonic acid groups compared to lithium. This means that the process also functions as a lithium purification process, as the purity of the LiOH will be higher than the input lithium formate solution. Polyvalent metals can be removed from the membrane to prevent clogging by stripping with acid or by briefly and periodically reversing the direction of the current to drive the polyvalent metals down the pH gradient back into the diluent.

[0101] This electrolysis process can be integrated into a lithium-ion battery recycling process or flowsheet when the feed to the diluent is the leachate from the selective formic acid leaching of lithium-ion battery black mass. In this case, the regenerated formic acid produced in the electrolysis can be reused in the leaching of the black mass. More generally, this process can be used to regenerate organic acids without oxidizing the organic anions at the anode, avoiding the use of anion exchange membranes or bipolar membranes, and to recover metals in hydroxide form from organic salts.

[0102] In the cell setup shown in Figure 17, there are three recirculating electrolytes. During electrolysis, lithium in the diluent (center chamber), which is a formic acid leach (e.g., 50% by volume), passes through the cathode side cation exchange membrane to balance the charge of the hydroxide ions produced by the cathode water splitting reaction, thereby forming LiOH. + The ions leave behind formate ions, whose negative charge is balanced by protons that diffuse across the cation exchange membrane on the anode side from the anolyte, and which are produced in the water splitting reaction at the anode. The anolyte is sulfuric acid, and its sole purpose is to be a conductive medium through which the protons can diffuse. The purpose of the cation exchange membrane between the anolyte and diluent is to prevent the formate ions from diffusing into the anolyte and being oxidized there. In the experimental set-up, three peristaltic pumps recirculate the electrolyte.

[0103] FIG. 18 shows the change in lithium concentration in the catholyte and anolyte with electrolysis. As expected, the concentration of lithium increases rapidly in the catholyte. Lithium also migrates to the anolyte, moving in the opposite direction to the current, and unlike in the catholyte, the concentration changes nonlinearly. The adjacent diluent is 14.3 gL -1Since the lithium starts out at a concentration of 1.0 g L−1, diffusion into the anolyte against the current is likely due to a large concentration gradient. In continuous operation, this is not an issue because the anolyte reaches a steady state lithium concentration where the driving force due to the concentration gradient equals the back driving force of the cell voltage. Over 80 minutes, the concentration of lithium in the diluent solution increases to 14.3 g L−1. -1 From 8.0gL -1 It decreased to.

[0104] Formic acid leaching is selective for lithium, but other metals are expected to be present in low concentrations. Previous experiments in sulfate media have shown that Nafion 115 membranes are selective for lithium, whereas Ni 2+ Li + It has been shown to be highly selective for monovalent cations such as . However, it was unclear whether the presence of formic acid would affect the selectivity of the membrane, so the electrolysis was re-run using a dilute solution with added impurities. The composition of the resulting solution (50% formic acid by volume) is shown in the table below.

[0105] The concentrations of elements in the synthetic leachate are as follows: [Table 1]

[0106] FIG. 19 shows the change in the concentration of lithium in the anolyte, diluent, and catholyte over time. FIG. 19 shows that while lithium moved from the diluent to the catholyte, it also moved from the anolyte to the diluent. The movement of lithium from the anolyte to the diluent was slower than the movement in the reverse direction. However, steady-state electrolysis studies appear to be the only way to operate a system with a constant lithium anolyte concentration.

[0107] Figure 20 shows the concentrations of selected elements in the anolyte, diluent, and catholyte. As in the sulfate system, polyvalent metals did not pass the membrane in significant amounts, but sodium passed the membrane readily. In the sulfate system, copper and zinc were the only polyvalent elements that passed the membrane. In the formate system, normalized to the initial concentration in the diluent, Na+ 2.2±0.1 Li per ion + Ions pass through the membrane and Mn 2+ 5000±1500 Li per ion + Ions pass through the membrane. In the sulfate system, there is no selectivity between sodium and lithium. However, there is a slight preference for lithium in the formate system. The difference in selectivity is likely caused by differences in the solubility of the metals and the local pH at the membrane.

[0108] Figure 21 shows the pH of the catholyte and anolyte versus time. As can be seen in Figure 21, the pH of the anolyte drops significantly. This is due to the Li lost to the diluent. + ions are replaced by protons generated at the anode. Interestingly, the pH of the catholyte increases in this experiment. This suggests that the formic acid crossover rate was significantly lower. This is best explained by the lower initial formic acid concentration of 39% compared to 50%. In this experiment, the flow of lithium from the anolyte was reversed so the pH of the diluent remained constant. By maintaining a higher pH throughout the experiment, a lower percentage of formic acid exists as associated neutral molecules, thereby further reducing crossover.

[0109] Figure 22 shows the concentrations of formate in the anolyte and catholyte during electrolysis, as determined by analysis of carbon concentration by ICP. A proximate standard was produced by dissolving sodium formate in sulfuric acid. Residual carbon in the blank standard, probably due to dissolution of CO2 from the air, meant that the calibration curve was non-linear and did not cross the origin, and furthermore, that the repeated ICP measurements had high error. The concentrations in Figure 22 are therefore not quantitative and are included here only to show the trend. It is clear that the concentration of formate in both the anolyte and catholyte increases over time, confirming that formic acid is passing through both membranes. Ion chromatography can be used to confirm and quantify the presence of formate in the anolyte and catholyte. As a result, formic acid passing through the anolyte is oxidized to CO2 at the anode and lost, while formic acid passing through the catholyte produces a mixture of lithium formate and lithium hydroxide.

[0110] Figure 23 shows a comparison of the change in lithium concentration in the catholyte between two experiments (AI3816 and AI3822). Comparing the two experiments in Figure 23, lithium is concentrated in the catholyte much more rapidly in AI3816, which has a higher starting lithium concentration in the diluent, resulting in a favorable concentration gradient. This leads to a large difference in current efficiency, which is 67% for AI3816 and 40% for AI3822.

[0111] Figure 24 shows a comparison of the cell voltages of AI3816 and AI3822. Figure 24 shows that the cell voltage decreases for AI3822 and increases slightly for AI3816. This is believed to be because the concentration of sulfuric acid in the anolyte remained relatively constant for AI3816 but increased for AI3822, thereby increasing the conductivity of the anolyte. Considering the cell voltage and current efficiency, the energy intensity to produce 1 kilogram of lithium hydroxide is 10.4 kWh kg for AI3816. -1 , 16.1kWh kg for AI3822 -1This is in the same range as the energy intensity of sulfate-based materials.

[0112] Considering the above, it has been shown that it is possible to electrolyze lithium formate to lithium hydroxide and formic acid using a three-chamber approach. The Nafion 115 cation exchange membrane shows good selectivity for lithium over all metals except sodium. However, there is some crossover of formic acid into the anolyte and catholyte, which needs to be minimized by selecting membranes that minimize such crossover or by using an improved approach, which is described in the next section.

[0113] Use of a "neutralization chamber" to eliminate formic acid crossover in the production of LiOH from lithium formate In this approach, crossover of formic acid from the diluent to the catholyte of the electrochemical cell is reduced by forcing the formic acid through a high pH solution to dissociate it and reduce its passage through a cation exchange membrane in contact with the concentrate. A pure LiOH solution can be produced under conditions with greatly reduced contamination of formate ions, and without significant loss of Li or formate.

[0114] In the electrolysis of the black mass formic acid leachate of lithium-ion batteries, which contains primarily lithium formate and 30-70% v / v formic acid in water, there is a problem with the loss of formic acid to the LiOH product of electrolysis because formic acid diffuses to some extent across the cation exchange membrane that separates the LiOH from the leachate. It exists primarily as a neutral molecule when the pH is below 3.75, and therefore is able to diffuse across the membrane. If formate exists as an anion, it will have a much harder time passing through the membrane because it will be electrostatically repelled by the negatively charged functional groups (e.g., sulfonate functional groups) of the cation exchange polymer.

[0115] When the formic acid leachate is directly adjacent to the LiOH and separated only by a cation exchange membrane, a pH gradient across the membrane exists, meaning that for much of the formic acid's path through the membrane the pH is below 3.75, allowing it to easily diffuse through to higher pH regions.

[0116] The method of this section almost completely eliminates formic acid crossover by placing a "neutralization chamber" between the leachate chamber and the LiOH product chamber in the electrochemical cell. The electrolyte in the neutralization chamber is a mixture of lithium formate and lithium hydroxide, whose pH is always maintained above pH 5. Formic acid passes from the leachate chamber through the first membrane into the neutralization solution / chamber, but then dissociates in the high pH solution, making it very difficult to pass through the second membrane into the LiOH product chamber. Li + The ions pass through a first cation exchange membrane into the neutralization chamber and then through a second cation exchange membrane into the LiOH catholyte. Small amounts of LiOH produced in the catholyte are supplied to the neutralization solution at a rate sufficient to neutralize the incoming formic acid by the following reaction: LiOH+HCO2H-->LiCO2H+H2O.

[0117] A small amount of neutralizing solution is bled off and fed to the diluent with the leachate so that no total lithium or formate is lost.

[0118] The overall cell configuration consists of an anode chamber with an electrolyte separated from the diluent by a cation exchange membrane. The anolyte can be LiOH, formic acid, or another suitable electrolyte. The diluent contains lithium formate / formic acid leach and is separated from the neutralizing solution by a cation exchange membrane. The neutralizing solution is a mixture of lithium formate and lithium hydroxide and is separated from the catholyte by a cation exchange membrane. The catholyte is lithium hydroxide.

[0119] Thus, the objective here is to force the formic acid to move through the high pH solution to reach the LiOH product. Above pH 5, nearly 100% of the acid dissociates and becomes very difficult to pass through the cation exchange membrane. As long as the neutralization solution is maintained above pH 5, crossover of formic acid to the LiOH product is minimized. The neutralization solution is recycled along with a small bleed of the LiOH product feed. As the formic acid passes through the membrane, it is neutralized by LiOH to LiCO2H. A small bleed of the neutralization solution is fed to the leachate to avoid loss of lithium and formate.

[0120] The hypothesis that a higher pH in the central neutralization chamber results in less crossover has been proven. Compared to cell configurations without such a neutralization chamber, crossover can be reduced by 99.7%. Furthermore, by selecting the appropriate membrane, crossover can also be reduced.

[0121] With the aim of reducing formic acid crossover in electrolysis, experiments were carried out to measure the flux of formic acid through Nafion 115 and Nafion 424 cation exchange membranes. The effect of formic acid concentration on the crossover rate was also investigated. Furthermore, an improved cell setup has been designed in which a central chamber is inserted between the formic acid feed chamber and the LiOH product chamber. The pH of the solution in the central chamber has been modified to test the hypothesis that a higher pH of the central solution would result in a lower crossover of formic acid into the LiOH product solution, due to dissociation of weak acids, thereby reducing its ability to pass through the cation exchange membrane.

[0122] As mentioned above, when formic acid is crossed over to LiOH during electrolysis, a mixture of lithium formate and lithium hydroxide is obtained, with LiOH being the desired product. If formic acid is crossed over to the anolyte, it is more likely to be lost to oxidation at the anode. Furthermore, the more formic acid is lost from the leachate, the less can be recycled.

[0123] In the cell configuration shown in Figure 25 (similar to that described in the previous section), the formic acid feed chamber is directly adjacent to the LiOH product chamber. In contrast, in the cell configuration shown in Figure 26, the formic acid feed chamber is separated from the LiOH product chamber by a "neutralization chamber." Experiments were conducted to test and compare the cell configurations shown in Figures 25 and 26 and the performance of different membranes for use in such configurations.

[0124] First, two different membranes, Nafion 115 and Nafion 424, were tested for formic acid and water crossover using a formic acid concentration of 50%. By switching from a Nafion 115 membrane (127 micrometers thick) to a Nafion 424 membrane (380 micrometers thick), the formic acid crossover was reduced by 62% and the water crossover was reduced by 69% (see Figures 27 and 28). It is also important to reduce the crossover of water into formic acid, as this causes dilution of the formic acid. Since it is desirable to reuse the formic acid produced from electrolysis in leaching, it is undesirable for the formic acid to be diluted in the electrolysis process.

[0125] The Nafion 424 membrane is thicker, but has a higher Li + This reduces back diffusion of ions and increases current efficiency. Therefore, there is no trade-off in terms of electrochemical performance by using this thicker membrane to reduce crossover. Another advantage of Nafion 424 is that it is reinforced with polymer fibers to increase mechanical strength. This greatly increases its durability in long-term use.

[0126] The effect of formic acid concentration on crossover was investigated using Nafion 424 membrane. As shown in Figure 29, as the concentration increases, the formic acid crossover rate increases, levels off, and then decreases. This means that if the formic acid concentration in the leachate is reduced to 30%, the formic acid crossover can be further significantly reduced. Another implication is that there is no disadvantage to increasing the formic acid concentration in the leachate to above 50%. This is advantageous because the leaching selectivity for Li increases with formic acid concentration.

[0127] While it is important to select a membrane that reduces formic acid crossover, it does not achieve the complete elimination of crossover to LiOH, which is desirable. Therefore, the improved cell configuration of FIG. 26 was designed to reduce or eliminate the remaining formic acid crossover. In this regard, formic acid passes through a cation exchange membrane much more easily when it is in solution as an associated neutral molecule than when it is dissociated into anions and cations. Formic acid has a pKa of 3.75 and dissociates almost completely above pH 5. Therefore, by forcing the formic acid to pass through an intermediate solution with a pH above 5 before it reaches LiOH, crossover can be reduced to negligible levels. There is also an additional benefit gained from the fact that it must diffuse through two membranes to reach LiOH, not just one.

[0128] Considering the above, an improved method is to operate a four-chamber cell instead of a three-chamber one, in which Li travels through a "neutralization chamber" between the leachate and LiOH. Formic acid from the leachate is neutralized by a small outflow of LiOH product that is fed into the neutralization chamber to form lithium formate. This lithium formate outflow is then fed into the diluent along with the leachate so that no lithium or formate ions are wasted. This approach is effective as long as the pH of the neutralization chamber solution is maintained above 5.

[0129] The three center chamber solutions used in the four-chamber cell configuration were water, 0.3 mol / L LiOH, and 0.3 mol / L H2SO4. The final pH of each solution plotted against the crossover rate of formic acid into water is shown in Figure 30. This supports the hypothesis that increasing pH decreases the crossover rate. When LiOH was used in the center chamber rather than water, the crossover rate decreased by 82.6%. If LiOH had been replenished, the crossover rate would have been even lower. The final pH of 3.5 suggests that all the LiOH was neutralized. At steady state operation, LiOH is replenished.

[0130] Crossover was essentially eliminated using a four-chamber configuration, as shown in Figure 31. Compared to the two-chamber experiment, the use of an additional central chamber with LiOH reduced crossover by 99.7% (both using Nafion 424 as the membrane).

[0131] In conclusion, this section shows that Nafion 424 significantly reduces the crossover of water and formic acid compared to Nafion 115. Furthermore, the hypothesis that a higher pH reduces the crossover was proven, and the use of an intermediate LiOH solution reduced the crossover to negligible (not measurable by titration) levels.

[0132] summary The present specification provides several methods for carrying out a process for recycling Li from an input material containing Li and one or more transition metals, the method including contacting the input material with a leaching medium comprising an organic acid (e.g., formic acid), leaching Li from the input material to form a leachate comprising lithium (e.g., lithium formate), and electrolytically decomposing the lithium (e.g., lithium formate) to lithium hydroxide. In the context of recycling battery materials from so-called "black lump" as an example, the process flows of Figures 3(a) and 3(b) have been realized and can be implemented in a battery material recycling flowsheet as shown in Figure 2 to remove lithium from the black lump prior to processing to extract, purify, and recycle other valuable metals, including cobalt and nickel. Several different electrochemical cell configurations for electrochemically converting lithium formate to lithium hydroxide have been described, including (i) a cell configuration based on a repeated two-chamber configuration, (ii) a three-chamber configuration, and (iii) a four-chamber configuration including a central neutralization chamber. Each of these configurations is tailored to provide a high purity LiOH product while allowing efficient recycling of formic acid. This is necessary for the lithium extraction approach to be economically and ecologically viable as a recycling method. The method can also be applied to the processing of lithium from other input materials containing Li and one or more transition metals.

[0133] The electrochemical processing techniques are described in the context of using formic acid, particularly concentrated formic acid, as an organic acid to leach lithium from the input material. In this regard, the use of concentrated formic acid has been found to be advantageous in that it selectively leaches lithium from the input material containing lithium and transition metals. However, the same electrochemical processing techniques are applicable even when a different organic acid is used for the leaching step. Examples of organic acids that can be used to leach lithium from the input material include formic acid, acetic acid, propionic acid, malonic acid, citric acid, butyric acid, oxalic acid, tartaric acid, or a mixture of several organic acids.

[0134] Thus, while the present invention has been particularly shown and described with reference to specific embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.

[0135] References 1.JP2012126583 2.JP2014173144 3.CN108689827A 4.JPWO2013153692A1 5.“Formic acid regeneration by electromembrane processes”, Journal of Membrane Science 280(2006)509-516. 6.“Electro-membrane processes for organic acid recovery”,RSC Adv.,2019,9,7854. 7. “Application of electrodialysis to the production of organic acids”, Journal of Membrane Science, 288 (2007) 1-12. 8.“Three-compartment bipolar membrane electrodialysis for splitting of sodium formate into formic acid and sodium hydroxide”, Journal of Membrane Science 325(2008)528-536. 9. “Three compartment bipolar membrane electrodialysis of sodium formate”, Journal of Membrane Science, 2008, 325, pp. 528-536. 10.“Electrodialysis in water-ethanol solutions”,Desalination 154(2003)9-15. 11.“Transport of formic acid through anion exchange membranes”,Separation Science and Technology,39:1,165-184,2005. 12.Gao et al.,Environ.Sci.Technol.,2017,51,1662-1669. 13.CN110233302A 14.WO2018192121 15.CN105244564B 16.CN110563044A 17.CN111621643A

Claims

1. A method for recycling lithium from an input material containing lithium and one or more transition metals, comprising: contacting the input material with a leaching medium containing an organic acid; leaching lithium from the input material to form a leachate containing an organic lithium salt; electrolytically converting the organic lithium salt to an inorganic lithium salt in an electrochemical cell, the electrochemical cell having an anode, a cathode, and one or more cation exchange membranes, the one or more cation exchange membranes being selective for the permeation of monovalent lithium over the permeation of polyvalent transition metals such that the electrochemical cell functions both in converting the organic lithium salt to the inorganic lithium salt and in separating the lithium from polyvalent transition metal impurities in the leachate; recycling the organic acid from the electrochemical cell for reuse in the contacting and leaching steps; comprising: a method.

2. The method according to claim 1, wherein the inorganic lithium salt is lithium hydroxide or lithium carbonate.

3. The organic acid in the leaching medium is formic acid, the leachate contains lithium formate, and the lithium formate is converted to the inorganic lithium salt in the electrochemical cell. The method according to claim 1 or 2.

4. The method according to claim 1 or 2, further comprising a polyvalent metal separation step applied to the leachate to remove polyvalent transition metal impurities prior to electrolysis of the leachate.

5. The method according to claim 1 or 2, wherein at least 50 wt%, 60 wt%, 70 wt%, 80 wt%, or 90 wt% of the organic acid in the leaching medium is recycled from the electrochemical cell.

6. The method according to claim 1 or 2, further comprising selectively precipitating the inorganic lithium salt formed in the electrochemical cell at a temperature of at least 60 °C, 70 °C, 80 °C, 90 °C, or 100 °C.

7. The method according to claim 6, wherein the supernatant from the precipitation is recycled to the electrochemical cell.

8. The method according to claim 6, further comprising washing the precipitated inorganic lithium salt and recycling the wash liquid to the electrochemical cell.

9. The electrochemical cell according to claim 1 or 2 comprises a dilution liquid chamber for receiving the leachate and a concentrate liquid chamber separated from the dilution liquid chamber by a cation exchange membrane, the cation exchange membrane blocking polyvalent transition metals and selectively allowing lithium ions to pass through the dilution liquid chamber and enter the concentrate liquid chamber to form the inorganic lithium salt in the concentrate liquid chamber.

10. The method according to claim 9, wherein the polyvalent transition metal is periodically removed from the cation exchange membrane by chemically stripping or periodically reversing the cell current.

11. The electrochemical cell comprises an anolyte chamber in contact with the anode, the anolyte chamber being separated from the dilution liquid chamber adjacent to the anolyte chamber by a bipolar membrane. The electrochemical cell according to claim 9 comprises a catholyte chamber in contact with the cathode, the catholyte chamber being separated from the concentrate liquid chamber adjacent to the catholyte chamber by a bipolar membrane.

12. The method according to claim 9, wherein the electrochemical cell comprises a pair of two or more dilution liquid chambers and concentrate liquid chambers.

13. The method according to claim 12, wherein the electrochemical cell comprises at least 3, 4, 6, 8, 10, 15, 20, 50, 100, 200, 300, or 350 pairs of dilution liquid chambers and concentrate liquid chambers.

14. The method according to claim 9, wherein the electrochemical cell comprises an anolyte chamber in contact with the anode, the anolyte chamber being separated from the dilution liquid chamber adjacent to the anolyte chamber by a cation exchange membrane.

15. The electrochemical cell further comprises a neutralization chamber disposed between the dilution liquid chamber and the concentrate liquid chamber. The method according to claim 9, wherein the neutralization chamber is maintained at a pH greater than 4, 5, or 6.

16. The electrochemical cell further comprises a neutralization chamber disposed between the dilution liquid chamber and the concentrate liquid chamber. The method according to claim 9, wherein the neutralization chamber is maintained at a pH greater than the pKa of the organic acid.

17. The method according to claim 1 or 2, wherein the input material contains, in addition to lithium, one or more of nickel, manganese, and cobalt.

18. The method according to claim 1 or 2, wherein the input material is a lithium battery scrap material.

19. In the anode of the electrochemical cell, H ＋ ions are generated, and in the cathode of the electrochemical cell, hydroxide ions are generated. The method according to claim 1 or 2.

Images