Lithium recovery from lithium-ion batteries

Abstract

To provide a method for lithium recovery from lithium-ion batteries.SOLUTION: Recycling of a charge material for an NMC (Ni, Mn, Co) battery recovers lithium from a recycled battery stream by: roasting a black mass from the recycled stream in a partial oxygen environment at a temperature based on thermal reduction of a cathode material; reacting carbon in an anode material with lithium in the cathode material; and then leaching the lithium from the roasted black mass for forming a lithium leach solution. Lithium is recovered by heating the lithium leach solution, and precipitating the lithium carbonate based on decreased solubility of the leached lithium carbonate at the increased temperature.SELECTED DRAWING: Figure 1

Description

[Background technology]

[0001] background Lithium-ion (Li-ion) batteries are the preferred chemistry for secondary (rechargeable) batteries in high discharge applications such as electric vehicles (EVs) and power tools where rapid acceleration of electric motors is required. Li-ion batteries include a charge material, conductive powder, and binder that is applied or deposited onto a current collector, typically a planar sheet of copper or aluminum. The charge material includes an anode material, typically graphite or carbon, and a cathode material that includes predetermined ratios of metals such as lithium, nickel, manganese, cobalt, aluminum, iron, and phosphorus, that define the so-called "battery chemistry" of a Li-ion cell. Summary of the Invention [Means for solving the problem]

[0002] overview Lithium recovery from lithium-ion (Li-ion) battery recycle streams involves roasting the black mass of mixed charge material in a partial oxygen environment, during which carbon from the anode material in the black mass combines with lithium from the cathode material in the black mass to form lithium carbonate. Subsequent refining upgrades the recycled lithium carbonate from industrial to battery grade. The balance of roasting temperature and available oxygen allows for a reaction to occur sequentially, first forming lithium oxide at the roasting temperature, and a second reaction in which Li combines with oxygen and the anode carbon, without the need to add a separate carbon source, such as activated carbon, to supplement the production of lithium carbonate.

[0003] The configurations herein are based, in part, on the observation that lithium recovery is advantageous for battery recycling to reduce costs, as opposed to providing a purified feedstock of high purity lithium. Unfortunately, conventional approaches to Li recovery suffer from the drawback that the carbon already readily available in the anode material of the recycle stream is supplemented with an additional source of carbon, such as activated carbon, to yield Li. This requires an additional carbon source to extract Li, and leaves additional carbon in the recycle stream that needs to be removed in a subsequent recycling step. Thus, the configurations herein substantially overcome the drawbacks of conventional additive carbon approaches by partial oxygen roasting, which consumes the carbon already present in the black mass from the anode material, but does not prevent the thermal reduction of the cathode material to recycle lithium as lithium carbonate.

[0004] An example configuration for recovering lithium from the recycle stream using an NMC (Ni, Mn, Co) battery involves roasting black mass from the recycle stream in a partial oxygen environment at a temperature selected for reductive decomposition of the cathode material, reacting the carbon in the anode material with the lithium in the cathode material, and then leaching lithium from the roasted black mass to form a lithium leach solution. Li precipitates from solution as Li2CO3 at elevated temperatures, and lithium is recovered by heating the lithium leach solution to precipitate lithium based on the reduced solubility of the leached lithium at elevated temperatures.

[0005] BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other features will be apparent from the following description of specific embodiments disclosed herein, as illustrated in the accompanying drawings, in which like reference characters refer to the same parts throughout the different drawings. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a flow diagram of partial oxygen roasting for Li recovery disclosed herein. [Diagram 2] FIG. 2 is a flow diagram of the purification of Li from the leachate of FIG. 1. [Diagram 3] 2 is a table showing the analysis results of the leachate of FIG. 1. [Figure 4] 3 is a table showing the results of Li purification in FIG. 2. [Diagram 5] The results of repeated leaching cycles are shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Detailed Description Example methods and techniques are described below for recycling batteries, such as Li-ion batteries, from a recycle stream of multiple battery chemicals, often nickel, manganese, cobalt, and aluminum in various ratios. Typically, current secondary (rechargeable) batteries use metals such as Ni, Mn, Co, and Al with binders and conductive materials as the cathode material, and graphite or similar forms of carbon as the anode material. Recycling typically begins with discharging and physical disassembly, crushing, and / or agitation of the battery casing structure, resulting in a granular, mixed material, referred to as "black mass," such as the cathode, anode, and various casing and conductor materials. Discarded or rejected electric vehicle (EV) batteries are often sought for recycling as their bulk raw charge material.

[0008] Conventional roasting methods for lithium recycling use an inert or reducing gas environment and include adding a carbon source such as activated carbon, despite the relative abundance of carbon from the anode material. In contrast, the configurations herein use a partial oxygen environment that utilizes the carbon already present in the black mass as a carbon source but does not impede the thermal reduction and decomposition of the cathode material. The configurations discussed below demonstrate that a small amount of oxygen in a partial O2 environment effectively activates the carbon in the anode material source without impairing the thermal reduction / decomposition of the NMC cathode material, thereby eliminating the need for additional activated carbon.

[0009] Black mass from recycled Li-ion batteries contains a mixture of impurities such as copper, aluminum and iron used in the anode and cathode charge materials and the physical battery casing and contacts that typically interconnect the individual cells in a configuration that engages with the EV that uses the battery pack. This black mass therefore contains granular forms of battery materials such as charge material metals, carbon / graphite, lithium and electrolyte in somewhat variable ratios based on the morphology and type of battery in the source recycle stream. The morphology may or may not be well defined depending on the battery chemistry and / or the vehicle manufacturer. However, regardless of the exact battery chemistry, the presence of significant amounts of lithium from the cathode and significant amounts of carbon from the anode can be expected.

[0010] Roasting black mass from recycled lithium-ion batteries facilitates the recovery of expensive metals such as Li, Ni, Mn and Co from spent batteries. However, conventional methods use inert (N2 or Ar) or reducing gas environments (H2 or CH4) to reduce the active transition metal ions of the cathode material. In inert environments, higher roasting temperatures are often required to complete the reduction, and activated carbon is added to promote the carbothermal reduction, although the black mass already has sufficient carbon from the anode graphite, increasing energy consumption and operating costs. In reducing environments, explosive or highly flammable gas components require strict safety control and impose additional costs for the environmental gas composition. Also, roasting black mass in an inert or reducing environment atmosphere often causes further reduction of the transition metals that form their alloys, which is problematic for the recovery of transition metals in downstream recycling targeting the charge material metals.

[0011] The configuration described below addresses the above problems by using a partial oxygen environment for roasting of black mass. It is believed that the partial oxygen in the roasting environment activates the relatively thermally stable graphite in the black mass, allowing the graphite to become a carbon source for carbothermal reduction. Secondly, the partial oxygen environment prevents the complete reduction of the transition metal ions to the metallic or alloy state, or even reduces the transition metal ions to less soluble oxidation states in dilute aqueous acidic solutions (mainly +2, e.g., NiO, CoO, and MnO). Thirdly, since the partial oxygen environment activates the graphite, it also allows the lithium material from the cathode to form lithium carbonate, increasing the lithium recovery yield compared to a conventional inert environment for similar roasting temperature and time. Furthermore, roasting of black mass in a partial oxygen environment is believed to consume less than 15%, such as only 9-12%, of the graphite in the black mass, and thus, most of the graphite can still be recovered as recycled anode material for lithium-ion batteries after leaching of the cathode metal ions. In other words, the recovery of lithium carbonate has negligible impact on the effectiveness of downstream carbon and charge material recovery. The effectiveness of the partial oxygen roasting environment over the inert gas environment is shown in Table 1.

[0012] [Table 1]

[0013] Figure 1 is a flow diagram of an embodiment of the method of partial oxygen roasting for Li recovery disclosed herein. With reference to Figure 1, the roasting process 100 includes roasting black mass provided from the recycle stream of a lithium-ion battery in a partial oxygen environment at a temperature above 500°C in step 102. The temperature can be based on thermal reduction / decomposition of the cathode material and reacting the carbon in the anode material with the lithium in the cathode material. The black mass is typically obtained as a result of the recycle stream of a Ni, Mn, Co (NMC) battery. The roasting converts the lithium in the black mass from the available carbon in the black mass from the anode material to lithium carbonate.

[0014] A partial oxygen environment is defined by an oxygen environment having an oxygen concentration lower than atmospheric oxygen and a nitrogen concentration higher than atmospheric nitrogen. In certain configurations, the percentage of partial oxygen is 2-10%, preferably 3-5%, balanced with an inert gas such as nitrogen or argon, defining an environment with less oxygen and more nitrogen (or other inert gas) than ambient atmosphere (i.e., air). The roasting temperature can be between 550°C and 700°C, preferably between 575°C and 650°C, whereby the carbon already present from the anode begins to react with oxygen (below 500°C, the carbon is expected to remain inert). It is believed that the roasting of the black mass causes a carbothermal reaction with oxygen in the partial oxygen environment without additional activated carbon. When the cathode material is exposed to >500°C, the transition metals in the cathode material are also thermally reduced and decomposed, and the lithium in the cathode is initially converted to lithium oxide. When carbon and oxygen are available, Li2O is converted to Li2CO3. Reactions (1) and (2) occur very rapidly and probably almost simultaneously: LiNi x Mn y Co z O2+heat→ Li2O+x[NiO / Ni]+y[MnO / Mn2O4]+z[CoO / Co3O4 / Co] (1) where 1≧x+y+z≧0.9; 0.99≧x≧0.33; 0.33≧y≧0.01; and 0.33≧z≧0.01, Li2O+C ( graphite ) +pO2→Li2CO3+(1-p)C ( graphite ) +q(CO2 / CO) (2) Here, in the environmental atmosphere, 0.1≧p≧0.01 and 0.1≧q≧0.01.

[0015] Since the black mass contains anode material with graphite and cathode material such as lithium and charge carrier metal, by roasting, the carbon from the graphite combines with oxygen in a partial oxygen environment to form CO and CO2, which combine with lithium to form water-soluble lithium carbonate, as demonstrated by equations (1) and (2). The heat treatment time of roasting can typically vary from 10 minutes to 120 minutes, preferably 30 to 60 minutes. After roasting as shown in FIG. 1, lithium compounds can be leached from the roasted black mass by stirring it in deionized water, as shown in step 104, to form a lithium leachate solution.

[0016] The lithium used in the disclosed techniques is a lithium salt that is combined with a charge material metal in a recycled source and precipitated as a lithium salt as the resulting lithium product. The examples herein show lithium carbonate as the resulting lithium salt, facilitated by its increased solubility at lower temperatures rather than higher temperatures, however other lithium products can be obtained.

[0017] The lithium product, Li2CO3, is the only water leachable compound in roasted black mass; the remainder is not soluble in water. Thus, lithium carbonate can be selectively leached from roasted black mass using deionized water. Filtration of the lithium leach solution separates the insoluble material from the dissolved lithium salts.

[0018] Furthermore, the electrolyte, typically LiPF6, is decomposed into lithium fluoride and phosphorus fluoride compounds (PF5, PF3, OPF3, HF, etc.) during roasting. The lithium carbonate leach solution is a weakly basic solution (pH=11-12). Therefore, a significant amount of aluminum is dissolved in the lithium leach solution, along with trace amounts of by-products (e.g. NiO, CoO, and LiF, etc.) and Li2CO3 crystal products, which are the only major impurities in the leach solution based on the soluble products at this pH. Sodium and sulfur impurities may result from the environmental conditions, which can be avoided by controlling the environment. The analysis of the leachate and products is shown in Figure 3 below.

[0019] As shown in step 106, the amount of deionized water added for leaching can be varied. For example, the ratio of water to heat treated black mass is about 5-40 weight ratio, preferably 15-20. The lithium leaching temperature is maintained at about 5-40°C, preferably about 20-30°C, and the stirring time is 10-240 minutes, preferably 20-60 minutes.

[0020] The solubility of Li2CO3 varies inversely with temperature, in contrast to most solutes. Thus, lithium recovery can be achieved by heating the lithium leach solution to precipitate lithium carbonate based on the reduced solubility of the leached lithium carbonate at the elevated temperature. For example, as shown in FIG. 1, the leached Li2CO3 is harvested in step 108 by separating and removing the unleached solids by filtration, followed by heating the filtrate to >90° C. for 10-120 minutes, preferably 30-60 minutes, as shown in step 114. The filtered unleached solids prior to heating of the leach solution contain delithiated NMC, typically decomposed NMC oxides such as NiO, MnO, Mn3O4, CoO, Co3O4, and unreacted graphite, as disclosed in step 110. The filtered solids can then be fed to an NMC and graphite recovery stream for further processing, as shown in step 112.

[0021] Filtration recovers the desired lithium product, lithium carbonate in the example of Figure 1, as shown in step 116. The aqueous filtrate can be recycled to step 104 for the leaching cycle. The resulting filtered lithium carbonate solids, as shown in step 118, are dried to a granular form, as shown in step 120. The dried lithium carbonate can then be further purified if necessary, an example of which is shown in Figure 2.

[0022] For example, the lithium carbonate product from step 120 of Figure 1 is at least technical grade (>99% purity) and can be upgraded to battery grade by simple purification 200. When lithium carbonate is dissolved in a carbonated water solution, the solubility of the lithium carbonate increases by more than five times due to the conversion of the less soluble lithium carbonate to the highly soluble lithium bicarbonate. However, Equation 3: Li2CO 3(s) +CO 2(g) +H2O (l) ⇔2LiHCO 3(l) (pH=7~8) (3) As indicated by , the impurities do not dissolve, remain in a solid state and are separated by filtration.

[0023] Equation 3 represents combining carbon dioxide with the recovered lithium carbonate to precipitate purified lithium carbonate. In step 202, the recovered lithium carbonate is dissolved in water to form a solution. For purification of lithium carbonate to battery grade lithium carbonate, Li2CO3 is dissolved in DI (deionized) water by carbonation (dissolving CO2 into solution) to form a carbonated solution, as illustrated in step 204. However, impurities in the lithium carbonate remain solid. The impurity solids can be removed by microfiltration using a filter membrane between 0.1 and 0.45 μm, as illustrated in step 206. Li2CO3 is then recovered by converting the more soluble LiHCO3 to the less soluble Li2CO3 with heat above 90° C., for example to a temperature of 95° C. or higher for an hour, as illustrated in step 208. Carbonation can be done by bubbling carbon dioxide through an aqueous solution of the leached lithium carbonate or by pressurizing the carbon dioxide, stirring, and forming carbon dioxide and undissolved solids. Once carbonation is complete, the aqueous solution of lithium bicarbonate achieves a pH between 7.0 and 8.5. The Li2CO3 precipitated by heating the lithium bicarbonate solution is filtered as shown in step 210, and the filtered yield is dried in step 212 to form battery grade lithium carbonate as disclosed in step 214. The resulting lithium carbonate is ready to be used as a lithium source of cathode material for recycled cells.

[0024] Figure 3 is a table of analytical results of the leachate of Figure 1. Small amounts of sodium, sulfur and aluminum can be removed by purification of Figure 2. It should be apparent that the process sequence of Figures 1 and 2 results in a battery grade lithium product in the form of lithium carbonate from the black mass of NMC or similar recycled batteries. The remaining black mass contains residual carbon (less than 15% is consumed) and delithiated charge material metals such as Ni, Mn, and Co.

[0025] An example of the above procedure is illustrated in Figures 4 and 5. In an example setup, a pilot rotary kiln is used to roast 20 Kg of black mass at 610°C for 30 minutes using 3.5-4.5% O2 balanced with N2.

[0026] In the example of Figures 4 and 5, 50 g of roasted black mass was added to 1 L of deionized water and the mixture was stirred for 30 minutes at ambient temperature (about 20°C). The solids were then removed by vacuum filtration using 1 μm filter paper. The filtrate was heated to >90°C for 1 hour. During heating of the filtrate, Li2CO3 precipitated out of solution due to its low solubility at this higher temperature. The Li2CO3 product is collected by vacuum filtration using a 0.45 μm filter membrane. The filtrate was fed to the subsequent leaching process using the same amount of roasted black mass by adding a small amount of deionized water that is lost during the cycle. This cycle was repeated 10 times.

[0027] The Li2CO3 product collected above was purified as shown in Figure 2. Thus, 12.6 g Li2CO3 was dispersed in 200 mL DI water, and CO2 was bubbled into the solution while mechanically stirring the mixture at 5-20 °C. CO2 aeration and stirring were continued until the solution pH reached 7.5-8.0. Undissolved solids were then removed by vacuum filtration using a 0.1-0.2 μm filter membrane. The filtrate was heated to >90 °C to convert the highly soluble LiHCO3 to the even less soluble Li2CO3. High purity (≥99.5%) Li2CO3 then precipitated from the solution, and the product was collected by vacuum filtration. The filtrate was recycled to the next purification solution.

[0028] Figure 4 is a table of the results of Li purification from Figure 2. As can be seen, significant impurities are removed by the purification process, especially aluminum and sodium. Figure 5 shows the results of 10 repeated cycles of Li recovery from Figure 1 to yield the intermediate lithium carbonate product before purification from Figure 2.

[0029] Although the systems and methods defined herein have been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail can be made therein without departing from the scope of the invention as encompassed by the appended claims. [Explanation of symbols]

[0030] 100 Roasting Process 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 202, 204, 206, 208, 210, 212, 214 process 200 Refining Process

Claims

1. 1. A method for recovering lithium from a battery recycle stream, comprising: roasting black mass from the battery recycle stream in a partial oxygen environment at a temperature based on the thermal reduction of the cathode material; leaching lithium from the black mass to form a lithium leach solution; and heating the lithium leach solution to recover the lithium as a precipitate.

2. 10. The method of claim 1, wherein the partial oxygen environment has an oxygen concentration less than atmospheric oxygen and a nitrogen concentration greater than atmospheric nitrogen.

3. 2. The method of claim 1, wherein the temperature for roasting the black mass is between 500°C and 700°C.

4. 10. The method of claim 1, wherein the black mass is infused with water.

5. 2. The method of claim 1, wherein the black mass is infused at a temperature between 5°C and 40°C.

6. 10. The method of claim 1, wherein the precipitate is lithium carbonate.

7. combining carbon dioxide with the recovered lithium precipitate and selectively dissolving lithium carbonate by converting highly soluble lithium bicarbonate in water to form a carbonate solution; 10. The method of claim 1 further comprising purifying the recovered lithium precipitate by filtering undissolved impurity solids.

8. 8. The method of claim 7, wherein the carbonate solution comprises lithium bicarbonate.

9. heating the carbonate solution to a temperature above 90°C to form purified lithium carbonate solids; 9. The method of claim 8, further comprising filtering to remove the purified lithium carbonate solids.

10. 1. A process for producing purified battery grade lithium carbonate from the black mass of a Li-ion battery recycle stream, comprising: heating the black mass from said recycle stream in a partial oxygen environment containing 3-5% oxygen balanced by nitrogen at a temperature between 575°C and 650°C for a time period of 15-60 minutes to produce torrefied black mass; leaching the roasted black mass in deionized water at a temperature between 5°C and 25°C with a ratio of water between 15 and 20 with stirring for 20 to 60 minutes to form a lithium leach solution; filtering the lithium leach solution to remove unleached solids; Lithium carbonate is removed from the lithium leach solution by heating to a temperature above 90°C for at least 30 minutes to remove Li due to its reduced solubility at higher temperatures. ２ CO ３ separating the solids; Separated Li ２ CO ３ dissolving the solid in a deionized water solution of carbonate and filtering the impurities as solids; heating the filtered deionized aqueous solution of carbonate to precipitate purified lithium carbonate as the temperature rises above 90°C.

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