Selective recovery of Li

Abstract

1. A method for selectively removing Li from an input material comprising Li and one or more transition metals, the method comprising: 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 containing a mixture of Li and one or more transition metals.

Background Art

[0002] The number of portable electronic devices (e.g., smartphones and laptops) that require rechargeable batteries is increasing year by year. As environmental concerns grow, the automotive industry is searching for alternatives to internal combustion engines, and rechargeable batteries offer one solution. As the number of consumers adopting hybrid vehicles and fully electric vehicles powered by rechargeable batteries increases, the global demand for rechargeable batteries is expected to increase.

[0003] Modern rechargeable batteries typically include a cathode material based on a transition metal oxide framework containing intercalated lithium. Examples include LiCoO2, LiMn2O4, LiFePO4, LiNiCoAlO2, and LiNi x Mn y Co z O2 (''NMC''). One material showing promise for automotive applications is ''NMC'' (lithium-nickel-manganese-cobalt), which is represented by the general formula LiNi x Mn y Co z O2, where x + y + z = 1. It is desirable to provide a route for recovering and recycling the metals used in the cathode material of the battery. This is particularly important for Co, Ni, and Li, and less important for Mn.

[0004] The recovery of Li, Ni, Mn, and Co from NMC materials has been previously studied. In a typical process, these metals are solubilized from cathode scrap using an acidic leaching medium (e.g., sulfuric acid) to form a leachate containing metal ions, which is then separated by a series of precipitates 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, although Mn, Co, and Ni are often contaminated with Li impurities. Li is usually the last material remaining in the solution, precipitating as, for example, Li2CO3. However, at this stage, the leachate contains sodium ions previously introduced when Fe, Al, and Cu precipitate and during solvent extraction. Li precipitation often uses Na2CO3 as a carbonate source, tending to produce Li2CO3 contaminated with Na2CO3, making it difficult to obtain high-purity Li from Li2CO3. Therefore, it is advantageous if Li can be removed from the cathode scrap upstream before pH adjustment.

[0005] In a paper by Gao et al. (Environ.Sci.Technol.2017,51,1662-1669), the authors describe the recovery of Li, Ni, Mn, and Co from NMC cathode scrap using a leaching solution containing aqueous formic acid and hydrogen peroxide. Formic acid plays a dual role in this process. Firstly, formic acid acts as a reducing agent to convert insoluble +3 transition metal ions present in NMC into soluble +2 ions. Hydrogen peroxide is added to assist this reduction. Secondly, formic acid forms complexes with Li(I), Ni(II), Mn(II), and Co(II) ions in solution.

[0006] In the aforementioned Gao paper, the effects of parameters including reducing agent content, formic acid concentration, solid-liquid ratio (S / L), temperature, and time on the selectivity of metals extracted from cathode scrap were investigated. In one experimental set, the recovery of Li, Ni, Mn, and Co from used NMC cathode material was investigated by treating the material with a formic acid solution for a period of 120 minutes at a leaching temperature of 60°C. As the formic acid concentration increased, the leaching rate of each metal increased. In each case, a larger proportion of Li leached compared to the amounts of Ni, Mn, or Co, but in all cases, significant amounts of Ni, Mn, and Co were present in the leaching solution, and significant amounts of Ni, Mn, and Co required separation by a subsequent precipitation step. Similar results were obtained when a mixture of diluted formic acid and H2O2 was used as the leaching medium. Over time, the Co(II), Ni(II), and Mn(II) ion content in the leachate reached its maximum and then began to decrease due to the precipitation of ions as hydroxides, although the leachate consistently contained significant amounts of transition metal ions. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Gao et al.(Environ.Sci.Technol.2017,51,1662-1669) [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In particular, to provide a simpler recycling route for lithium-ion battery scrap, it is advantageous to provide a method that can selectively remove Li from input materials. This specification addresses this challenge. [Means for solving the problem]

[0009] In this specification, a method for selectively removing Li from an input material comprising Li and one or more transition metals, The process involves bringing the input material into contact with a leaching medium containing formic acid, The steps include leaching Li from the input material to form an leachate, A method is described in which the concentration of formic acid in the leaching medium is at least 40% by weight.

[0010] The inventors have surprisingly established that it is possible to selectively leach Li from the input material when the concentration of formic acid in the leaching medium is sufficiently high. This is particularly surprising considering that the results by Gao et al. (Environ. Sci. Technol. 2017, 51, 1662-1669) show that Ni, Mn, and Co all leach when a diluted aqueous formic acid solution is used as the leaching medium (corresponding to approximately 20% by weight of formic acid, with a maximum formic acid concentration of 4.5 mol / L).

[0011] While we do not wish to be bound by any theory, the high selectivity for Li leaching is thought to be a result of the poor solubility of transition metals at high concentrations of formic acid used in the processes described herein. In contrast, lithium ions are highly soluble in formic acid and form soluble lithium formate in situ. In previous reports on the separation of these metals from NMC cathode scrap, only the use of diluted formic acid was investigated (Environ. Sci. Technol. 2017, 51, 1662-1669), but under conditions of using diluted formic acid, Ni(II), Co(II), and Mn(II) have considerable solubility in the leaching medium. [Brief explanation of the drawing]

[0012] [Figure 1] Results obtained 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. [Figure 2]The results were obtained using NMC-111 as the input material, with 98% formic acid used as the leaching medium along with (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. [Figure 3] The results were obtained using NMC-111 as the input material, with a 77.5 wt% formic acid / 22.5 wt% water azeotrope 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. [Figure 4] The results were obtained using NMC-111 as the input material, with a 77.5 wt% formic acid / 22.5 wt% water azeotrope used together with (NH4)2SO4 as an additive 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. [Figure 5] The results were obtained using eLNO as the input material, with a solution of 50 wt% formic acid / 45 wt% water / 5 wt% H2O2 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. [Modes for carrying out the invention]

[0013] In this specification, a method for selectively removing Li from an input material comprising Li and one or more transition metals, The process involves bringing the input material into contact with a leaching medium containing formic acid, The steps include leaching Li from the input material to form an leachate, A method is described in which the concentration of formic acid in the leaching medium is at least 40% by weight.

[0014] The process described herein is carried out in an input material comprising lithium and one or more transition metals. The input material is typically a solid. The material is typically battery scrap, and is typically a mixture of anode scrap and cathode scrap from lithium-ion batteries, in particular cathode scrap from lithium-ion batteries.

[0015] Battery scrap may or may not have been previously used in an electrical energy storage device. Battery scrap can be waste material generated during the manufacture of batteries or materials, including, for example, waste intermediate materials or damaged batches. In some embodiments, the battery scrap is formed by mechanical and / or chemical treatment of waste lithium-ion batteries.

[0016] 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.

[0017] As will be understood by those skilled in the art, the input material may further include other elements and / or materials derived from an electrochemical storage device, such as other elements derived from cathode materials, current collectors, anode materials, electrolytes, and any battery or cell casing.

[0018] In a preferred embodiment, 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.

[0019] The input material may include at least 10 wt% Ni, such as 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 may include up to 80 wt% Ni, such as 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 may include 10 - 80 wt% Ni based on the total mass of the input material.

[0020] The input material may contain at least 0% by weight of Mn, for example, at least 1% by weight, at least 2% by weight, at least 5% by weight, or at least 10% by weight of Mn, based on the total mass of the input material. The input material may contain up to 33% by weight of Mn, for example, up to 30% by weight, up to 28% by weight, or up to 25% by weight of Mn, based on the total mass of the input material. The input material may contain 0 to 33% by weight of Mn, based on the total mass of the input material.

[0021] The input material may contain at least 0% by weight of Co, 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 contain up to 33% by weight of Co, for example, up to 30% by weight, up to 28% by weight, or up to 25% by weight of Co, based on the total mass of the input material. The input material may contain 0 to 33% by weight of Co, based on the total mass of the input material.

[0022] The input material may contain at least 0 wt% Li, for example, 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 may contain up to 20 wt% Li, for example, 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 may contain 0 to 20 wt% Li, based on the total mass of the input material.

[0023] The input material may contain at least 0 wt% Fe, for example, at least 1 wt%, at least 2 wt%, or at least 3 wt% Fe, based on the total mass of the input material. The input material may contain up to 10 wt% Fe, for example, up to 9 wt%, up to 8 wt%, or up to 7 wt% Fe, based on the total mass of the input material. The input material may contain 0 to 10 wt% Fe, based on the total mass of the input material.

[0024] The input material may contain at least 0% by weight of Al, for example, at least 1% by weight, at least 2% by weight, or at least 3% by weight of Al, based on the total mass of the input material. The input material may contain up to 10% by weight of Al, for example, up to 9% by weight, up to 8% by weight, or up to 7% by weight of Al, based on the total mass of the input material. The input material may contain 0 to 10% by weight of Al, based on the total mass of the input material.

[0025] The input material may contain at least 0 wt% Cu, for example, 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 may contain up to 20 wt% Cu, for example, 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 may contain 0 to 20 wt% Cu, based on the total mass of the input material.

[0026] The input material may contain at least 0% by weight of carbon (C) based on the total mass of the input material, for example, at least 1% by weight, at least 5% by weight, at least 10% by weight, or at least 15% by weight of carbon. The input material may contain up to 50% by weight of carbon (C) based on the total mass of the input material, for example, up to 45% by weight, up to 40% by weight, or up to 30% by weight of carbon. The input material may contain 0 to 50% by weight of carbon (C) based on the total mass of the input material.

[0027] The input material may contain 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.

[0028] Two important parameters to consider in the leaching process 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 10 g of Li and 9 g of Li is leached after leaching, the leaching efficiency for Li is 90%.

[0029] Leach selectivity refers to the ratio of a given metal leached to the total amount of metal leached. In the following figure, leaching selectivity is plotted based on the total molar content of metal ions in the leaching medium. For example, if the medium contains 0.95 mol of Li and 0.05 mol of Ni (total 1.0 mol of metal) after leaching, the leaching selectivity for Li is 95%. Leach selectivity is often reported based on the total weight percentage of the leached metal, but this can obscure the selectivity because Li has a low mass compared to other metals.

[0030] The process uses a leaching medium containing formic acid at a concentration of at least 40% by weight. The highest selectivity for Li removal is achieved using essentially pure formic acid (98+% formic acid, see examples) and / or high temperature, but in some embodiments, it may be preferable to use a relatively diluted formic acid leaching medium, e.g., a leaching medium of at least 40% by weight formic acid with up to 60% by weight water, or a leaching medium of at least 50% by weight formic acid with up to 50% by weight water. While such solutions are not as selective for Li removal as 98+% formic acid, the use of such solutions does not present the same engineering challenges as high concentrations of formic acid, which require more expensive plant equipment. The use of relatively diluted formic acid leaching mediums is also preferable from a safety standpoint because they are 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. Therefore, the use of a relatively diluted formic acid leaching medium may be particularly acceptable when the substrate is substantially free of Mn.

[0031] Typically, the leaching medium contains formic acid at a concentration of at least 70% by weight. The inventors have found that such a leaching medium exhibits high leaching selectivity for Li. In preferred embodiments, the concentration of formic acid in the leaching medium is at least 80% by weight. In preferred embodiments, the concentration of formic acid in the leaching medium is at least 90% by weight, e.g., at least 98% by weight, e.g., at least 99% by weight. Generally, higher concentrations of formic acid in the leaching medium result in higher leaching selectivity for Li. A substantially pure formic acid leaching medium has the advantage of being more efficient in removing Li and having higher selectivity for Li than other transition metals, particularly Ni, Mn, and Co.

[0032] In some embodiments, the leaching medium is an azeotrope of formic acid and water, containing 77.5% by weight formic acid and 22.5% by weight water. As those skilled in the art will understand, the azeotrope boils without changing the formic acid-to-water ratio. This allows the leaching medium to be more easily recycled, for example, by boiling and removing it from the solvent in the leaching solution. Since formic acid is consumed during the leaching process (for example, by the formation of lithium formate), the recycling loop generally includes the step of ensuring that the azeotrope composition is maintained in the reactor by adding a new leaching medium having a higher concentration of formic acid than the concentration of formic acid in the azeotrope, for example.

[0033] In some embodiments, the leaching medium contains H2O2. In addition to formic acid, H2O2 helps reduce 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 to 10% by weight, preferably 3 to 7% by weight. Lower H2O2 concentrations are desirable from a safety standpoint.

[0034] In some embodiments, leaching may be performed by agitating the substrate, for example, by stirring or using ultrasound, in order to ensure efficient contact between the leaching medium and the input material.

[0035] The inventors have established that, generally, higher temperatures during the leaching process result in higher leaching efficiency and selectivity. During the leaching process, the mixture of the leaching medium and the input material is preferably heated to a temperature of at least 40°C. To achieve high leaching efficiency, the temperature during the leaching process is typically at least 60°C. Preferably, the temperature during the leaching process is at least 80°C, and in some embodiments, at least 90°C. In some embodiments, the mixture is heated, for example, under reflux, to a temperature above the boiling point of the leaching medium.

[0036] The duration of heating should be sufficient to remove substantially all 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. Unnecessarily long durations are inconvenient for cost reasons. An appropriate duration will be readily apparent to those skilled in the art. When leaching is performed as a batch process, a typical duration of heating is 5 to 120 minutes, preferably 5 to 60 minutes.

[0037] The input material is typically brought into contact 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 contact with the input material, without further heating of the mixture. Alternatively, the leaching medium may be at ambient temperature when it comes into contact with the input material, and then the mixture may be heated to the desired temperature. It is also possible that the leaching medium is preheated before contact with the input material, and then the mixture is further heated to the desired temperature.

[0038] A key parameter in the leaching process is the ratio of solid input material to leaching medium, known as S / L. During the leaching process, metals dissolve in the leaching medium as metal formate, of which Li formate is the most soluble. The formation of metal formate is also associated with the generation of water, which dilutes the leaching medium (for example, when the substrate is a metal oxide).

[0039] The use of a high S / L ratio is preferable for several reasons, including lower raw material costs, lower plant operating costs, and a lower amount of leaching medium required, which means lower waste. At a high S / L ratio, the resulting leachate has a high concentration of lithium formate, which helps to suppress the dissolution of less soluble metal formates, such as Mn, Ni, or Co. On the other hand, at a high S / L ratio, the leaching medium tends to be diluted by water formed as a byproduct of the leaching process, which is unfavorable for leaching selectivity. Generally, an S / L ratio of at least 10 g / L, preferably at least 20 g / L, and more preferably at least 30 g / L is preferred. A typical range of values ​​for S / L is 10 to 150 g / L, for example 20 to 150 g / L, or for example 30 to 150 g / L.

[0040] In some embodiments, additives may be added to the leaching medium to further prevent the leaching of transition metals in the input material, thereby improving the 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 properties of the salt are not particularly important, as long as the salt has high solubility in the leaching medium and does not hinder the leaching of Li or interfere with downstream steps. A preferred class of salts is sulfates discovered by the inventors to prevent the leaching of transition metals, particularly Mn. The properties of the counterions in the sulfates are not particularly important, but it is preferable that the counterions are nonmetallic to avoid the unnecessary contamination of the leaching medium with additional metals. A preferred additive is ammonium sulfate. Additives may 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 amounts of 10–100 g / L, for example, 20–80 g / L, or 20–50 g / L, and these values ​​are particularly suitable for ammonium sulfate.

[0041] The process described herein results in the selective leaching of Li from an input material. While we do not wish to be bound by theory, it is assumed that formic acid (and H2O2, if present) first reduces the metal ions in the input material, allowing Li ions to dissolve in the leaching medium. The resulting output material is a transition metal oxide. Over time, this is thought to react with excess formic acid to produce the corresponding metal formate and water. Since the metal formate has poor solubility in the leaching medium, the metal formate remains solid.

[0042] The present invention will now be described by the following non-limiting embodiments. [Examples]

[0043] material NMC 111 - Supplier: Targray Formic Acid - 98% Grade Fisher Scientific Ammonium sulfate - supplied by Acros Organics Lithium nickel cobalt oxide cathode material, trade name eLNO(trademark), is available from Johnson Matthey Plc.

[0044] 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 suspension was stirred at 500 rpm while the solution was heated to a boil (approximately 103°C), which typically required the heating plate to be set to 130°C. After 1 hour, the solution was filtered, and the leachate was analyzed for elemental analysis using ICP-OES.

[0045] Figure 1 shows that within one hour, over 90% of Li leached from NMC 111, with Li accounting for over 90% by weight of the metal in the leaching solution. As the temperature increased, the leaching efficiency for Li increased without any indication of change in leaching selectivity. Only small amounts of Mn dissolved in the leaching medium under each condition, and Mn increased slightly with increasing temperature. Leaching of Co and Ni was minimal.

[0046] Example 2 (98 wt% formic acid + NMC 111 + (NH4)2SO4) The procedure of Example 1 was followed, but 2 g of (NH4)2SO4 was added to the leachate.

[0047] Figure 2 shows that although the leaching efficiency was not as high as that of Example 1, at temperatures above 60°C, the leaching selectivity was higher than that of Example 1, and there was almost no leaching of Ni, Co, or Mn.

[0048] Example 3 (77.5% by weight formic acid / 22.5% by weight H2O + NMC111) Instead of 50 mL of formic acid, 50 mL of an azeotrope of formic acid and water (77.5% formic acid and 22.5% H2O) was used, and the procedure of Example 1 was followed.

[0049] Figure 3 shows that while the use of formic acid / water azeotrope as a leaching medium still yielded high leaching efficiency, the leaching selectivity was not as high as that achieved when using 98% formic acid. Leaching of Mn(II) ions was particularly pronounced at higher temperatures.

[0050] Example 4 (77.5% by weight formic acid / 22.5% by weight H2O + NMC111 + (NH4)2SO4) The procedure for Example 3 was followed, but 2 g of (NH4)2SO4 was added to the leaching medium.

[0051] Figure 4 shows that, compared to the use of formic acid / water azeotrope alone (Example 3), the inclusion of (NH4)2SO4 resulted in higher selectivity for Li and lower concentrations of undesirable metal ions in the leachate. In particular, Mn leaching was suppressed.

[0052] Example 5 (50% by weight formic acid / 45% by weight H2O + 5% H2O2 + eLNO) The procedure of Example 1 was followed, but a mixture of 50 wt% formic acid, 45 wt% water, and 5 wt% H2O2 as the leaching medium, and 2 g of lithium nickel cobalt oxide cathode material were used instead of 2 g of NMC 111.

[0053] Figure 5 shows that high efficiency and relatively high selectivity of Li could be achieved using diluted performic acid as the leaching medium, but the leaching selectivity was not as high as that of Examples 1-4, which used a more concentrated leaching medium.

Claims

1. A method for selectively removing Li from an input material containing Li and one or more transition metals, The steps include bringing the input material into contact with a leaching medium containing formic acid and sulfate, The process includes the step of leaching Li from the input material to form a leachate, A method wherein the concentration of formic acid in the leaching medium is at least 70% by weight.

2. The method according to claim 1, wherein the input material includes, in addition to Li, one or more of nickel, manganese, and / or cobalt.

3. The method according to claim 1 or 2, wherein the input material includes nickel, manganese, and cobalt in addition to Li.

4. The method according to any one of claims 1 to 3, wherein the concentration of formic acid in the leaching medium is at least 80% by weight.

5. The method according to any one of claims 1 to 4, wherein the concentration of formic acid in the leaching medium is at least 95% by weight.

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

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

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

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

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

11. The leaching medium is (NH ４ ) ２ SO ４ The method according to any one of claims 1 to 10, including the method described in any one of claims 1 to 10.

12. The method according to any one of claims 1 to 11, wherein the leaching is performed by stirring the input material.

13. The method according to claim 12, wherein the stirring is performed by stirring.

14. The method according to claim 12 or 13, wherein the stirring is performed by ultrasonic waves.

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