Anode recovery in recycled batteries

Abstract

A method for recycling anode material from a co-recycled stream of depleted lithium-ion batteries includes receiving a residual amount of precipitate from the cathode recycle stream. This precipitate is almost entirely graphite used for recycling battery anode material. The precipitate is produced by acid leaching of charging material from the lithium-ion battery recycle stream. A strong acid is added to the precipitate to remove residual cathode and separator material, and the mixture is heated. The strong acid removes residual alumina from the separator by conversion to aluminum sulfate. The acid-treated precipitate is washed to remove water-soluble contaminants, such as aluminum sulfate generated from the reaction of alumina and sulfuric acid, to produce substantially pure graphite. Any residual material remaining from the cathode recycle stage is also removed.

Description

Background Technology

[0001] Cathode material recycling is a major focus for lithium-ion (Li-ion) batteries, which are widely used in automotive, personal electronics, and industrial applications. However, the waste stream from recycled batteries typically involves indiscriminate agitation (crushing and shredding) of the entire battery assembly, resulting in contamination of cathode, anode, separator, and casing materials. Recycling processes for cathode material recovery often result in significant amounts of unused and / or discarded anode material. Summary of the Invention

[0002] The anode material recycling process recovers a secondary stream from the acid leaching of the cathode material. Anode material recycling collects the solid particulate residue from the acid leaching of the cathode material from the mixed recovery stream rich in both cathode and anode materials from disassembled batteries. Due to the economics of collecting new materials, the recycling of raw materials from spent or depleted batteries, such as that disclosed in U.S. Patent No. 9,834,827 (incorporated herein by reference), tends to focus on the cathode material. However, anode materials (such as graphite) also have value as recycling materials.

[0003] The configuration described in this paper is based on the observation that the modern trend of electric vehicle (EV) production creates a significant demand for secondary (rechargeable) batteries, and a corresponding need to dispose of or recycle these batteries at the end of their lifespan. Unfortunately, anode materials, primarily composed of inexpensive graphite and / or carbon, are considered unsuitable for large-scale recycling, among their cathode counterparts. Therefore, the configuration described in this paper essentially overcomes the drawbacks of anode recycling by receiving anode material along with a complementary cathode recycling process and purifying already refined graphite for use as anode material in the recycling process. Since graphite has already undergone most of the processing and refining associated with the production of battery-grade graphite, recycling from waste is more efficient than refining new graphite.

[0004] A method for recycling anode material from a co-existing recovery stream from a depleted lithium-ion battery involves receiving a residual precipitate from the cathode recovery stream via a membrane filter press, such that the precipitate contains approximately 6-7% alumina and 4-5% by weight of metal sulfate impurities. The remainder of this precipitate is almost entirely graphite used for recycling battery anode material. The precipitate is produced by acid leaching of the feedstock from the lithium-ion battery recovery stream. A strong acid (such as 98% H₂SO₄) is added to the precipitate to remove residual cathode and membrane material, and the mixture is heated to approximately 300°C. Leaching the cathode material (typically nickel, manganese, and cobalt) typically leaves alumina, which was previously used as the membrane material between the cathode and anode sides of the battery. The strong acid removes the alumina from the membrane by converting it to aluminum sulfate. Washing the acid-treated precipitate removes water-soluble contaminants, such as aluminum sulfate produced by the reaction of alumina and sulfuric acid, to produce substantially pure graphite. Any residual NMC (Ni, Mg, Co) remaining from the cathode recycling stage is also removed.

[0005] Because the value of the raw material (graphite) is lower than that of the cathode material, the anode material receives less attention in conventional recycling. Furthermore, conventional anode processing uses hydrogen fluoride (HF) at extremely high temperatures, thus introducing significant safety overhead. The method proposed herein uses a safer material at much lower temperatures, thereby achieving cost-effective anode recycling. Moreover, the original anode material used for recycling can be derived from the cathode recycling method disclosed in the aforementioned '827 patent.

[0006] Additional characteristics include qualitative separation and classification of graphite types. Battery manufacturers use specified ratios of natural and synthetic graphite, further distinguishing different particle sizes because natural graphite exhibits a "flaky" structure. The composition ratio of natural to synthetic graphite from the lithium-ion battery recycling stream is determined by testing or identifying the known source composition from which the recycled batteries are produced. The resulting pure graphite is sorted or labeled to maintain the composition ratio in the substantially pure graphite produced, typically approximately 60% / 40% synthetic to natural graphite, or alternatively 55% / 45%. The purity of the harvested purified graphite is approximately 98.5% based on several factors listed below.

[0007] Anode recycling methods primarily target the recovery of graphite from battery recycling streams, thus benefiting from the prior processing and purity of the graphite used in first-generation batteries. Anode material from depleted batteries typically undergoes impurity treatment before being used in first-generation batteries. Any impurities in this anode material are confined to the surface of the graphite particles in the anode material.

[0008] Based on the known suppliers (vehicle manufacturers) and the chemical composition of the lithium-ion batteries used by each manufacturer, the determination of the EV (electric vehicle) recycling stream is further organized. The known composition of the feed anode material is maintained based on the recycling stream of batteries originating from specific manufacturers. A uniform stream is maintained so that this known composition can be carried into the resulting pure graphite. In other words, if the feed stream is limited to known suppliers, then feed batteries from the same manufacturer with sheet graphite of a 60% / 40% ratio and a certain size composition will be recycled into pure graphite with a similar composition. Attached Figure Description

[0009] The above and other objects, features, and advantages of the present invention will become clear from the following description of specific embodiments of the invention as illustrated in the accompanying drawings, in which the same reference numerals refer to the same parts throughout different views. These drawings are not necessarily to scale, but rather focus on illustrating the principles of the invention.

[0010] Figure 1 This is a flowchart of the anode material recycling process disclosed in this article;

[0011] Figure 2A-2B It comes from Figure 1 SEM (Scanning Electron Microscopy) images of the recycled raw materials in the process; and

[0012] Figure 3 Is using Figure 1 The charging characteristics of the raw materials. Detailed Implementation

[0013] With the advent of electric and hybrid vehicles, the demand for electrochemical energy storage, typically in the form of batteries, is increasing. The configurations described below facilitate the recycling of aged or depleted feedstocks from spent batteries to recover active feedstocks with a specific NMC molar ratio (expressed as Ni:Mn:Co). Commonly used cathode material types are 60%:20%:20% (622), 80%:10%:10% (811), 50%:30%:20% (532), and 33.3%:33.3%:33.3% (111). Cathode feedstock precursors are derived from the sulfate forms of Ni, Mn, and Co, as defined in U.S. patents and applications, including US9,834,827, 10,522,884, 10,741,890, and application number 16 / 164,952.

[0014] While the elements of cathode materials are generally more conducive to recycling, the anode feedstock, primarily composed of graphite and carbon, is also generated through recycling. Subsequent processing also allows for the recovery of this anode feedstock. Leaching of cathode materials (such as nickel, manganese, and cobalt), along with the chemical and physical removal of byproducts (such as current collector metals and sealing materials), results in a graphite / carbon residue, with approximately 15% alumina and sulfate material remaining. Substantially pure graphite can be produced through subsequent processing using strong acids and moderate heating, as described further below.

[0015] Figure 1 This is a flowchart of the anode material recycling process disclosed in this paper. (Reference) Figure 1 In step 110, a precipitate comprising graphite is received as a byproduct or waste stream from the recycling operation of the battery cathode material. As mentioned above, conventional methods do not seek the recovery of anode material (primarily graphite); in contrast, the method of this paper incorporates graphite recycling as a complementary process to cathode recycling. Therefore, the received precipitate is the remaining feedstock from a previously acid-leached battery feedstock used for recycling. Any suitable recycling or other process can be employed to obtain the graphite precipitate, but in a particular configuration, the precipitate is obtained from a previously leached feedstock derived from an NMC (nickel, manganese, cobalt) recycling stream, typically representing previously used feedstock in rechargeable batteries for electric vehicles. According to the aforementioned U.S. patent, one particular method includes acid leaching. EVs have large-size batteries and will continue to represent a recycling stream parallel to the vehicle's lifespan. More specifically, these NMC batteries are lithium-ion batteries (LIBs) and are already widely used in millions of electric vehicles (EVs) and plug-in electric vehicles.

[0016] Graphite used in anode materials has morphological or shape characteristics that define the batch or quantity of bulk graphite. Natural graphite typically has flake characteristics and corresponding dimensions, further discussed in Table II below. Synthetic graphite is more expensive and usually has a powder or granular texture. The production of anode materials from natural flake graphite requires processing. Historically, this processing has yielded one ton of anode-grade graphite from every three tons of flake graphite concentrate. Even with modern production efficiencies, losses associated with graphite upgrading are in the range of 30%–50% before final purification. The configuration described in this paper describes the recycling of lithium-ion batteries from electric vehicles and the recovery of high-purity graphite with morphologies and blends (natural and synthetic) specifically designed for electric vehicle applications. Since the graphite has been upgraded for battery use, the recovery efficiency is approximately 98%.

[0017] In conventional methods, to bring graphite to final anode material specifications, anode companies use hydrogen fluoride (HF) or inert high-temperature baking to upgrade the graphite from approximately 94% total graphitic carbon (Cg) to 99.95% Cg. These expensive and environmentally burdensome chemical and thermal treatments are required to remove impurities deep within the material's core. However, the impurities found in BR graphite are located on the graphite surface and are therefore easier to remove using cheaper and more environmentally friendly methods.

[0018] Because graphite has been previously processed for use in batteries, it has been refined and does not require the extensive processing that first-generation natural and synthetic graphite underwent during initial use. Furthermore, since the general composition is known from the battery structure, unwanted components can be identified by type and volume. Typically, the precipitate from the recycle stream contains less than 11% impurities. More specifically, the precipitate typically contains less than 7% alumina and less than 5% metal sulfates. These parameters are known from the battery structure and previous cathode and anode recycle feeds.

[0019] A method for recycling anode material from a co-extracted recycle stream of depleted lithium-ion batteries includes washing the precipitate generated from the acid leaching of the feedstock from the lithium-ion battery recycle stream in step 112. This eliminates any remaining water-soluble components in the NMC recycling / leaching. An alternative method involves separating alumina via a foam flotation step, based on alumina with a density lower than graphite, as disclosed in step 115. Aluminum is typically used in current collectors and can therefore be expected to account for approximately 7% of the precipitate.

[0020] A strong acid, such as sulfuric acid 114, is added to the precipitate to remove residual cathode and diaphragm material, as shown in step 116. This involves heating the mixture of the strong acid and the residual cathode and diaphragm material to a temperature based on the desired purity of the resulting anode material. Recall that the precipitate is retained from a previous acid leaching of the cathode material, thus it can be concluded that the strong acid is stronger (with a lower pH) than the acid used in the acid leaching of the precipitate from the recovery stream. Sulfuric acid is particularly suitable for both cathode and anode leaching; in this specific instance, the strong acid is sulfuric acid with a concentration of at least 98%. Generally, increasing the temperature and heating time increases purity. Specific combinations that yield the desired purity are shown in Table I:

[0021]

[0022] Table I

[0023] Other acids can be used. For example, based on the acid strength of the combined acids, strong acids can be formed by combining sulfuric acid with one or more other acids. One specific arrangement involves forming a strong acid from a mixture of about 80% sulfuric acid and 20% nitric acid. However, any suitable inorganic acid or mixture of inorganic acids, such as hydrochloric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrobromic acid, perchloric acid, and / or hydroiodic acid, can be used to produce the purified anode material as described above.

[0024] Sulfuric acid can be regenerated to recover sulfuric acid in a repeated manner for continuous recycling batches, as shown in step 118.

[0025] As shown in step 120, after the heating step, an optional additional step includes a secondary leaching to improve the purity of the resulting graphite. The secondary leaching can be carried out using either dilute hydrochloric acid or dilute sulfuric acid.

[0026] Based on the information in Table 1 or alternative temperature and time parameters, as shown in step 122, the precipitate is further washed to remove water-soluble contaminants, thereby producing graphite of the desired purity. This removes water-soluble aluminum compounds.

[0027] As shown in step 126, the now purified precipitate is fractionated to concentrate the material for new recycled batteries. Typically, this involves determining the composition ratio of natural to synthetic graphite from the lithium-ion battery recycling stream used for the precipitate and maintaining that composition ratio in the resulting substantially pure anode material. In other words, the precipitate morphology known from the feed recycling stream is preserved. The morphology of graphite is further detailed in Table II:

[0028]

[0029] Table II

[0030] Synthetic graphite has become a preferred material for lithium-ion batteries due to its purity, performance, and consistency. As an anode material, synthetic graphite enables better cycle stability, faster charging, higher quality consistency, and rapid production scalability. The chart also shows that synthetic graphite significantly drives up costs. Therefore, battery manufacturers define formulations regarding battery composition, often driven by receiving automakers. This composition (based on the morphology of graphite in the battery) is determined and maintained through recycling, ensuring it can be sold back to manufacturers specifying particular compositions.

[0031] High-quality synthetic graphite is synthesized from needle coke. The global market for needle coke is highly fragmented, dominated by a few large producers, but limited by the technical requirements of needle coke as a crude oil refining byproduct. Growing demand for needle coke from the steel and lithium-ion battery industries, coupled with tightening environmental regulations, appears poised to create strong price headwinds.

[0032] While natural graphite originates from mines around the world, its purity and flake size vary considerably. To convert natural graphite into the selected size, ultrapure, spherical material required for battery applications, rigorous selection of starting materials is necessary to ensure long-term consistency and stability. Although graphite is a fairly common mineral on Earth, not all mines produce the required consistent large flakes as a starting point for economically producing the desired product specifications. Therefore, it is generally preferred to produce substantially pure graphite with a morphology based on the defined form of natural graphite. The resulting product is essentially pure graphite, as shown in step 128.

[0033] Figure 2A-2B It comes from Figure 1 SEM (Scanning Electron Microscopy) image of the recycled feedstock in the process flow. (Reference) Figure 2A and 2B SEM also demonstrated the impact of the purification process. Figure 2A SEM images of raw graphite from spent lithium-ion batteries are shown, and Figure 2B It shows the basis Figure 1 The process of purifying graphite. For example... Figure 2A As shown, severe agglomeration and a large amount of residue were observed in graphite. However, after the purification process, the agglomeration and residue decreased. Figure 2B The number of cases has decreased and even disappeared because Figure 2B The recycled graphite exhibits better refined single-particle quality, indicating that impurities were effectively removed through the recycling process. No significant morphological changes were observed in the graphite particles, suggesting that the graphite's morphology was not damaged during purification. Furthermore, the recycled graphite has a smoother and clearer surface compared to the virgin graphite, indicating a significant reduction in impurities.

[0034] Figure 3 Is using Figure 1 The charging characteristics of the raw materials. Figure 3 The rate performance of recycled graphite anodes is shown. The discharge capacity of recycled graphite at 0.1 C is 377.3 mAh / g, which is very close to that of commercial graphite.

[0035] While the systems and methods defined herein have been specifically shown and illustrated with reference to their embodiments, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as covered by the appended claims.

Claims

1. A method for recovering graphite from a recycled stream of a depleted lithium-ion battery, the method comprising: Receive a mixed lithium-ion battery recycling stream after dismantling lithium-ion batteries, wherein the mixed lithium-ion battery recycling stream includes cathode material and anode material; The cathode material in the mixed lithium-ion battery recycling stream is leached using an aqueous acid leaching solution; A precipitate containing graphite and impurities is generated from the aqueous acid leaching solution, wherein the impurities include alumina and metal sulfates; After the aqueous acid leaching of the cathode material is completed, a strong acid is added to the resulting precipitate to remove impurities and form a mixture. The strong acid causes the pH value to be lower than the pH value of the acid leaching solution in which the precipitate was generated. The mixture is heated at a temperature between 250°C and 350°C; as well as The precipitate is washed to remove water-soluble contaminants, thereby producing purified graphite.

2. The method of claim 1, wherein the precipitate has less than 11 wt% impurities.

3. The method of claim 1, wherein the purified graphite has less than 7 wt% alumina and less than 5 wt% metal sulfate.

4. The method of claim 3, further comprising separating the alumina by a foaming flotation step, which is based on alumina with a density lower than that of graphite.

5. The method of claim 1, wherein, The hybrid lithium-ion battery recycling stream is the remaining material from the recycling stream of previously acid-leached battery raw materials used for recycling.

6. The method of claim 5, wherein, The hybrid lithium-ion battery recycling stream is derived from previously leached cathode material from the NMC (nickel, manganese, cobalt) recycling stream.

7. The method of claim 1, further comprising receiving the hybrid lithium-ion battery recycling stream by recycling from a waste stream of previously used raw materials used in the rechargeable batteries of an electric vehicle.

8. The method of claim 1, wherein, The strong acid is sulfuric acid with a concentration of at least 98%.

9. The method of claim 1, further comprising: Determine the composition ratio of natural graphite to synthetic graphite generated from the recycled lithium-ion battery stream; and The determined composition ratio is maintained in the purified graphite produced.

10. The method of claim 9, further comprising determining the morphology of the natural graphite, and The graphite is produced to have a morphology based on the defined morphology of the natural graphite.

11. The method of claim 1, further comprising, after the heating step, performing a secondary leaching to improve the purity of the resulting graphite.

12. The method of claim 11, wherein, The secondary leaching is carried out using either dilute hydrochloric acid or dilute sulfuric acid.

13. The method of claim 1, further comprising generating the strong acid by combining the sulfuric acid with one or more other acids.

14. The method of claim 1, further comprising forming the strong acid from a mixture of 80% sulfuric acid and 20% nitric acid.

15. The method of claim 1, wherein, The strong acid is an inorganic acid or a mixture of inorganic acids, including acids selected from the group consisting of: sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, boric acid, hydrofluoric acid, hydrobromic acid, perchloric acid, and hydroiodic acid.

16. The method of claim 1, wherein, The mixture is heated at a temperature of at least 250°C for 6 hours to achieve a purity of at least 97.0%.

17. The method of claim 1, wherein, The mixture is heated at a temperature of at least 350°C for 2 hours to achieve a purity of at least 99.3%.

18. The method of claim 1, wherein, The mixture is heated at a temperature of at least 350°C for 24 hours to achieve a purity of at least 99.7%.

19. The method according to claim 1, wherein, The precipitate includes at least the anode material remaining after aqueous acid leaching of cathode material containing Ni, Mn and Co raw materials.

20. The method of claim 1, further comprising: To perform hydrometallurgical recovery, the temperature is maintained at 350°C or below.

21. The method according to claim 1, wherein, The resulting precipitate originates from the acid leaching of a granular Ni, Mn, Co recovery stream comprising cathode and anode materials, and the acid leaching extracts sulfates of Ni, Co, and Mn from the granular Ni, Mn, Co recovery stream.

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