Selective recovery of Li

Abstract

A method for selectively removing Li from an input material comprising Li and one or more transition metals, the method comprising the steps of: contacting the input material with a leaching medium comprising formic acid; and leaching Li from the input material to form a leachate; wherein the concentration of formic acid in the leaching medium is at least 70% by weight.

Description

Technical Field

[0001] This specification relates to the selective recovery of Li from an input material comprising a mixture of Li and one or more transition metals. Background Technology

[0002] The number of portable electronic devices requiring rechargeable batteries, such as smartphones and laptops, is increasing year by year. With growing environmental concerns, the automotive industry is seeking alternatives to internal combustion engines, and rechargeable batteries offer a solution. As consumers increasingly adopt hybrid and all-electric vehicles powered by rechargeable batteries, global demand for rechargeable batteries is expected to only grow.

[0003] Modern rechargeable batteries typically incorporate cathode materials based on lithium-intercalated transition metal oxide frameworks. Examples include LiCoO2, LiMn2O4, LiFePO4, LiNiCoAlO2, and LiNi. x Mn y Co z O2 (“NMC”). One material showing promise in automotive applications is “NMC” (lithium-nickel-manganese-cobalt), which is composed of the general formula LiNi. x Mn y Co z O2 represents the form where x + y + z = 1. The aim is to provide pathways for recycling and reusing metals used in battery cathode materials. This is particularly important for Co, Ni, and Li, and to a lesser extent for Mn.

[0004] The recovery of Li, Ni, Mn, and Co from NMC materials has been previously studied. In typical methods, the metals in the cathode waste are dissolved using an acidic leaching medium (e.g., sulfuric acid) to form a leachate containing metal ions, followed by pH adjustment and / or solvent extraction, separating the metals through a series of precipitations. 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 to remain in solution and precipitates, for example, as Li₂CO₃. However, at this stage, the leachate contains sodium ions, which were introduced earlier during the precipitation of Fe, Al, and Cu, and during solvent extraction. Li precipitation often uses Na₂CO₃ as a carbonate source and tends to produce Li₂CO₃ contaminated with Na₂CO₃, from which it is difficult to obtain high-purity Li. Therefore, it would be advantageous to remove Li upstream of the cathode waste before pH adjustment.

[0005] In their paper (Environmental Science & Technology, 2017, 51, 1662-1669), Gao et al. described the recovery of Li, Ni, Mn, and Co from NMC cathode waste using a leaching solution comprising aqueous formic acid and hydrogen peroxide. Formic acid plays a dual role in this method. First, it acts as a reducing agent, converting insoluble +3 valent transition metal ions present in the NMC into soluble +2 valent ions. The addition of hydrogen peroxide aids this reduction reaction. Second, formic acid forms complexes with Li(I), Ni(II), Mn(II), and Co(II) ions in the solution.

[0006] The paper by Gao mentioned above investigated the effects of parameters including reducing agent content, formic acid concentration, solid-to-liquid ratio (S / L), temperature, and time on the selectivity of metals extracted from cathode waste. In a series of experiments, the recovery of Li, Ni, Mn, and Co from spent NMC cathode material was studied by treating it with formic acid solution at a leaching temperature of 60°C for 120 minutes. The leaching rate of each metal increased with increasing formic acid concentration. Although a larger proportion of Li was leached relative to the amount of Ni, Mn, or Co in each case, significant amounts of Ni, Mn, and Co were present in the leachate, requiring separation through subsequent precipitation steps. Similar results were obtained when a mixture of dilute formic acid and H₂O₂ was used as the leaching medium. Although the content of Co(II), Ni(II), and Mn(II) ions in the leachate reached its maximum over time, and then began to decrease as these ions precipitated as hydroxides, a considerable amount of transition metal ions remained in the leachate.

[0007] To provide a simpler recycling pathway, particularly for Li-ion battery waste, it would be advantageous to provide a method capable of selectively removing Li from the input material. This specification addresses this issue. Summary of the Invention

[0008] This document describes a method for selectively removing Li from an input material comprising Li and one or more transition metals, the method comprising the following steps:

[0009] Contact the input material with a leaching medium comprising formic acid; and

[0010] Li is leached from the input material to form a leachate;

[0011] The concentration of formic acid in the leaching medium is at least 40% by weight.

[0012] The inventors of this invention unexpectedly determined that Li in the input material could be selectively leached if the concentration of formic acid in the leaching medium was sufficiently high. This was surprising, especially considering the results of Gao et al. (Environmental Science & Technology, 2017, 51, 1662-1669), which showed that Ni, Mn, and Co were all leached when a dilute aqueous formic acid solution was used as the leaching medium (formic acid concentration at most 4.5 mol / L, corresponding to approximately 20% by weight of formic acid).

[0013] Without being bound by any theoretical framework, it is generally believed that the high selectivity of Li leaching is a consequence of the poor solubility of transition metals when using high concentrations of formic acid in the method described in this paper. In contrast, Li ions exhibit high solubility in formic acid and form soluble lithium formate in situ. Previous reports on the separation of these metals from NMC cathode waste have only investigated the use of dilute formic acid (Environmental Science & Technology, 2017, 51, 1662-1669), under which Ni(II), Co(II), and Mn(II) exhibit considerable solubility in the leaching medium. Attached Figure Description

[0014] Figure 1 Results for NMC-111 as input material, using 98% formic acid as the leaching medium. 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.

[0015] Figure 2 The results show the leaching media selection for NMC-111 as input material, using 98% formic acid as the leaching medium and (NH4)2SO4 as an additive. The image on the left shows the leaching media selection, and the image on the right shows the leaching media efficiency.

[0016] Figure 3 The results for leaching NMC-111 as input material using a 77.5 wt% formic acid / 22.5 wt% water azeotrope as the leaching medium 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.

[0017] Figure 4 The results show the leaching media for NMC-111 as input material, using 77.5 wt% formic acid / 22.5 wt% water azeotrope as the leaching medium and (NH4)2SO4 as an additive. 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.

[0018] Figure 5The results were obtained using a solution of 50 wt% formic acid / 45 wt% water / 5 wt% H2O2 as the leaching medium for 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. Detailed Implementation

[0019] This specification describes a method for selectively removing Li from an input material comprising Li and one or more transition metals, the method comprising the following steps:

[0020] Contact the input material with a leaching medium comprising formic acid; and

[0021] Li is leached from the input material to form a leachate;

[0022] The concentration of formic acid in the leaching medium is at least 40% by weight.

[0023] The method described in this specification is applied to an input material comprising lithium and one or more transition metals. The input material is typically a solid. The material is typically battery waste, typically a mixture of anode and cathode waste from Li-ion batteries, particularly cathode waste from Li-ion batteries.

[0024] Battery waste may have been previously used in an energy storage device, but this is not necessary. Battery waste can be waste material generated during the manufacture of batteries or materials, including, for example, discarded intermediate materials or substandard batches. In some embodiments, battery waste is formed by mechanically and / or chemically processing discarded lithium-ion batteries.

[0025] 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.

[0026] Those skilled in the art will understand that the input material may additionally include other elements and / or materials derived from electrochemical energy storage devices, such as those derived from cathode materials, current collectors, anode materials, electrolytes, and other elements from any battery or battery casing.

[0027] In a preferred embodiment, the material includes one or more of nickel, manganese, and cobalt in addition to Li. In some embodiments, the material also includes each of nickel, manganese, and cobalt in addition to Li.

[0028] The input material may include at least 10% by weight, for example, at least 12%, at least 15%, at least 20%, or at least 25% by weight of Ni, based on the total mass of the input material. The input material may also include up to 80% by weight, for example, up to 75%, at most 70%, or at most 50% by weight of Ni, based on the total mass of the input material. Finally, the input material may include between 10% and 80% by weight of Ni, based on the total mass of the input material.

[0029] The input material may include at least 0% by weight, for example, at least 1%, at least 2%, at least 5%, or at least 10% by weight of Mn, based on the total mass of the input material. The input material may also include up to 33% by weight, for example, up to 30%, at most 28%, or at most 25% by weight of Mn, based on the total mass of the input material. Finally, the input material may include from 0% to 33% by weight of Mn, based on the total mass of the input material.

[0030] The input material may include at least 0% by weight, for example, at least 1% by weight, at least 2% by weight, at least 5% by weight, or at least 10% by weight of Co, based on the total mass of the input material. The input material may also include up to 33% by weight, for example, up to 30% by weight, at most 28% by weight, or at most 25% by weight of Co, based on the total mass of the input material. The input material may also include from 0% to 33% by weight of Co, based on the total mass of the input material.

[0031] The input material may include at least 0% by weight, for example, at least 1%, at least 2%, at least 5%, or at least 6% by weight of Li, based on the total mass of the input material. The input material may also include up to 20% by weight, for example, up to 18%, at most 15%, or at most 12% by weight of Li, based on the total mass of the input material. The input material may also include from 0% to 20% by weight of Li, based on the total mass of the input material.

[0032] The input material may include at least 0% by weight, for example, at least 1%, at least 2%, or at least 3% by weight of Fe, based on the total mass of the input material. The input material may also include up to 10% by weight, for example, up to 9%, at most 8%, or at most 7% by weight of Fe, based on the total mass of the input material. The input material may also include from 0% to 10% by weight of Fe, based on the total mass of the input material.

[0033] The input material may include at least 0% by weight, for example, at least 1%, at least 2%, or at least 3% by weight Al, based on the total mass of the input material. The input material may also include up to 10% by weight, for example, up to 9%, at most 8%, or at most 7% by weight Al, based on the total mass of the input material. The input material may also include from 0% to 10% by weight Al, based on the total mass of the input material.

[0034] The input material may include at least 0% by weight, for example, at least 1%, at least 2%, or at least 3% by weight of Cu, based on the total mass of the input material. The input material may also include up to 20% by weight, for example, up to 15%, up to 10%, up to 9%, up to 8%, or up to 7% by weight of Cu, based on the total mass of the input material. Finally, the input material may include from 0% to 20% by weight of Cu, based on the total mass of the input material.

[0035] The input material may include at least 0% by weight, for example, at least 1% by weight, at least 5% by weight, at least 10% by weight, or at least 15% by weight, based on the total mass of the input material. The input material may also include up to 50% by weight, for example, up to 45% by weight, at most 40% by weight, or at most 30% by weight, based on the total mass of the input material. The input material may also include from 0% to 50% by weight, based on the total mass of the input material.

[0036] The input materials may include 10% to 80% by weight of Ni, 0% to 33% by weight of Mn, 0% to 33% by weight of Co, 0% to 20% by weight of Li, 0% to 10% by weight of Fe, 0% to 10% by weight of Al, 0% to 10% by weight of Cu, and 0% to 50% by weight of C, based on the total mass of the input materials.

[0037] Two important parameters to consider in leaching methods are leaching efficiency and leaching selectivity. Leaching efficiency is the proportion of a given metal in the input material that is leached by the leaching medium. For example, if the input material contains 10g of Li, and after leaching, 9g of Li is leached, then the leaching efficiency of Li is 90%.

[0038] Leach selectivity refers to the proportion of a given metal leached relative to the total amount of metal leached. In the accompanying figure, 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 mol of Li and 0.05 mol of Ni (totaling 1.0 mol of metal), the leaching selectivity for Li is 95%. Sometimes leaching selectivity is reported as the total weight percentage of the leached metal, but this can be misleading because Li has a relatively small mass compared to other metals.

[0039] The method uses a leaching medium comprising at least 40% by weight formic acid. While the highest selectivity for Li removal is achieved using substantially pure formic acid (98+% formic acid, see examples) and / or high temperatures, in some embodiments, the use of relatively dilute formic acid, such as at least 40% by weight formic acid and up to 60% by weight water, or at least 50% by weight formic acid and up to 50% by weight water, is preferred as the leaching medium. Although such solutions are less selective for Li removal than 98+% formic acid, their use does not present the same difficult engineering challenges as highly concentrated formic acid, which requires expensive plant equipment. From a safety perspective, the use of a relatively dilute formic acid leaching medium is also preferred because it is less flammable than concentrated formic acid. It has been shown that manganese salts are particularly detrimental to Li leaching selectivity due to their high solubility in aqueous formic acid solutions. Therefore, the use of a relatively dilute formic acid leaching medium is particularly permissible when the matrix is ​​substantially free of Mn.

[0040] Typically, the leaching medium comprises formic acid at a concentration of at least 70% by weight. The inventors of this invention have discovered that such leaching media exhibit high leaching selectivity for Li. In a preferred embodiment, the concentration of formic acid in the leaching medium is at least 80% by weight. In a preferred embodiment, the concentration of formic acid in the leaching medium is at least 90% by weight, for example, at least 98% by weight, for example, at least 99% by weight. Generally, the higher the concentration of formic acid in the leaching medium, the higher the leaching selectivity for Li. A substantially pure formic acid leaching medium has the advantages of high Li removal efficiency and high selectivity for Li relative to other transition metals, particularly Ni, Mn, and Co.

[0041] In some embodiments, the leaching medium is an azeotrope of formic acid and water containing 77.5 wt% formic acid and 22.5 wt% water. Those skilled in the art will understand that the azeotrope boils without altering the formic acid to water ratio. This allows the leaching medium to be recycled more directly, for example, by removing the solvent from the leachate through boiling. Since formic acid is consumed during the leaching process (e.g., by producing lithium formate), the recycling loop typically includes a step of ensuring the azeotropic composition is maintained in the reactor by, for example, adding fresh leaching medium with a formic acid concentration greater than that in the azeotrope.

[0042] In some embodiments, the leaching medium comprises H2O2. Besides formic acid, H2O2 also facilitates the reduction of transition metals in the input material (e.g., from a +3 or +4 oxidation state to a +2 oxidation state). When present in the leaching medium, the concentration of H2O2 in the leaching medium is preferably in the range of 1-10% by weight, more preferably in the range of 3-7% by weight. From a safety perspective, a lower H2O2 concentration is desirable.

[0043] To ensure efficient contact between the leaching medium and the input material, in some embodiments, leaching can be performed by agitating the matrix, for example by stirring or ultrasonically agitating the matrix.

[0044] The inventors of this invention have determined that, generally, the higher the temperature during the leaching process, the higher the leaching efficiency and leaching selectivity. Preferably, during the leaching process, the mixture of the leaching medium and the input material is heated to a temperature of at least 40°C. 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 at a temperature equal to or higher than the boiling point of the leaching medium, for example, under reflux.

[0045] The heating duration should be sufficient to remove substantially all Li from the input material. This can depend in part on the temperature of the leaching medium and the physical form and chemical properties of the input material. Unnecessarily long durations are undesirable for cost reasons. Those skilled in the art will readily determine a suitable duration. When leaching is performed in batches, typical heating durations are 5–120 minutes, preferably 5–60 minutes.

[0046] The input material is typically contacted with the leaching medium at room temperature or higher, and then heated to a desired temperature. In some embodiments, the leaching medium may be preheated before contacting the input material, rather than further heating the mixture. Alternatively, the leaching medium may be at ambient temperature upon contact with the input material, and then the mixture may be heated to a desired temperature. Alternatively, the leaching medium may be preheated before contacting the input material, and then the mixture may be further heated to a desired temperature.

[0047] A crucial parameter in leaching methods is the ratio of solid input material to leaching medium, known as S / L. During leaching, metals dissolve in the leaching medium as metal formates, with lithium formate exhibiting the highest solubility. The formation of metal formates is also related to water generation (e.g., when the matrix is ​​a metal oxide), which dilutes the leaching medium.

[0048] Using a high S / L ratio is advantageous for several reasons, including: the need for a smaller volume of leaching medium, which translates to lower raw material costs, lower plant operating costs, and reduced waste volume. At a high S / L ratio, the resulting leachate has a high concentration of lithium formate, which helps suppress the dissolution of less soluble metal formates, such as formates of Mn, Ni, or Co. On the other hand, at a high S / L ratio, the leaching medium is more easily diluted by water generated as a byproduct of the leaching process, which is detrimental to leaching selectivity. Generally, it is preferred that the S / L ratio is at least 10 g / L, more preferably at least 20 g / L, and more preferably at least 30 g / L. Typical ranges for S / L values ​​are 10-150 g / L, for example 20-150 g / L, and for example 30-150 g / L.

[0049] In some embodiments, additives may be added to the leaching medium to further prevent the leaching of transition metals from the input material and thereby improve the leaching selectivity for Li. The use of additives may be particularly suitable when the S / L ratio is high and / or the leaching medium has a relatively low concentration of formic acid. The properties of the salt are not particularly important, as long as it has high solubility in the leaching medium and does not interfere with the leaching of Li or disrupt downstream steps. A preferred class of salts is sulfate, which the inventors of this invention have found to prevent the leaching of transition metals, particularly Mn. The properties of the counterion in the sulfate are not particularly important, but the counterion is preferably nonmetallic to avoid unnecessary contamination of the leaching medium by other metals. A preferred additive is ammonium sulfate. The additive may be added to the leaching medium before or after contact with the input material. Typically, the additive is added to the leaching medium in amounts of 10-100 g / L, for example 20-80 g / L or 20-50 g / L, which are particularly suitable in the case of ammonium sulfate.

[0050] The method described in this paper induces the selective leaching of Li in the input material. Without being bound by theory, it is generally accepted that the initial formic acid (and H₂O₂, if present) reduces the metal ions in the input material, thereby 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 exists in solid form due to its poor solubility in the leaching medium.

[0051] The present invention will now be illustrated using the following non-limiting examples.

[0052] Example

[0053] Material

[0054] NMC 111—Supplier: Targray

[0055] Formic acid - 98% grade Fisher Scientific

[0056] Ammonium sulfate — supplied by Organics

[0057] Lithium nickel cobalt oxide cathode material, marketed under the trade name eLNO TM Purchased from Johnson Matthey PIc

[0058] Example 1 (98% formic acid by weight + NMC 111)

[0059] In a 100 mL round-bottom flask equipped with a condenser, add 2 g of NMC 111 to 50 mL of formic acid. Stir the suspension at 500 rpm while heating the solution to boiling (approximately 103 °C), typically requiring the heating plate to be set to 130 °C. After 1 hour, filter the solution and perform elemental analysis of the leachate using ICP-OES.

[0060] Figure 1 The results showed that >90% of Li was leached from NMC 111 within 1 hour, and Li accounted for >90% by weight of the metal in the leachate. The leaching efficiency of Li increased with increasing temperature, while the leaching selectivity showed no change. Under each condition, only a small amount of Mn dissolved in the leaching medium, with the amount of dissolved Mn increasing slightly with increasing temperature. The leaching of Co and Ni was negligible.

[0061] Example 2 (98% formic acid + NMC 111 + (NH4)2SO4)

[0062] Follow the procedure of Example 1, but add 2g of (NH4)2SO4 to the leachate.

[0063] Figure 2 The results show that although the leaching efficiency is not as high as that of Example 1, the leaching selectivity is higher than that of Example 1 at 60°C or higher, and there is almost no leaching of Ni, Co or Mn.

[0064] Example 3 (77.5 wt% formic acid / 22.5 wt% H2O + NMC111)

[0065] Following the procedure in Example 1, replace 50 mL of formic acid with an azeotrope of 50 mL of formic acid and water (77.5% formic acid and 22.5% H2O).

[0066] Figure 3 The results show that using formic acid / water azeotrope as the leaching medium still provides high leaching efficiency, but the leaching selectivity is not as high as that when using 98% formic acid. The leaching of Mn(II) ions is significant, especially with increasing temperature.

[0067] Example 4 (77.5 wt% formic acid / 22.5 wt% H2O + NMC111 + (NH4)2SO4)

[0068] Follow the procedure of Example 3, but add 2g of (NH4)2SO4 to the leaching medium.

[0069] Figure 4 The results show that, compared to using only formic acid / water azeotropes (Example 3), including (NH4)2SO4 resulted in higher selectivity for Li and lower concentrations of undesirable metal ions in the leachate. Specifically, Mn leaching was inhibited.

[0070] Example 5 (50% formic acid by weight / 45% H₂O + 5% H₂O₂ + eLNO)

[0071] The procedure of Example 1 was followed, but the leaching medium was a mixture of 50% by weight formic acid, 45% by weight water and 5% by weight H2O2, and 2g of lithium nickel cobalt oxide cathode material was used instead of 2g of NMC 111.

[0072] Figure 5 The results show that using diluted performic acid as the leaching medium can achieve high efficiency and relatively high selectivity for Li, but the leaching selectivity is not as high as in Examples 1-4, which used more concentrated leaching media.

Claims

1. A method for selectively removing Li from an input material comprising Li and manganese, the method comprising the steps of: The input material is brought into contact with a leaching medium comprising formic acid and sulfate; as well as Li is leached from the input material to form a leachate; The concentration of formic acid in the leaching medium is at least 70% by weight.

2. The method according to claim 1, wherein the concentration of formic acid in the leaching medium is at least 80% by weight.

3. The method according to claim 1, wherein the concentration of formic acid in the leaching medium is at least 95% by weight.

4. The method according to any one of claims 1 to 3, wherein the leaching medium comprises H2O2.

5. The method according to any one of claims 1 to 3, wherein the step of leaching Li from the input material to form a leachate involves heating to a temperature of at least 60°C.

6. The method according to any one of claims 1 to 3, wherein the step of leaching Li from the input material to form a leachate involves heating to a temperature of at least 80°C.

7. The method according to any one of claims 1 to 3, wherein the step of leaching Li from the input material to form a leachate involves heating at least to the boiling point of the leaching medium.

8. The method according to any one of claims 1 to 3, wherein the step of leaching Li from the input material to form a leachate involves heating under reflux.

9. The method according to any one of claims 1 to 3, wherein the leaching medium comprises a nonmetallic sulfate.

10. The method according to any one of claims 1 to 3, wherein the leaching medium comprises (NH4)2SO4.

11. The method according to any one of claims 1 to 3, wherein the leaching is carried out by agitating the matrix.

12. The method of claim 11, wherein the agitation is performed by stirring.

13. The method of claim 11, wherein the agitation is performed using ultrasound.

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