HK1237993B - Method for recycling positive-electrode material of a lithium-ion battery - Google Patents

Description

Method for recycling positive electrode material of lithium ion battery

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has a paid-up license in this invention and has the right, in limited circumstances, to require the patent owner to license others on reasonable terms as provided under the terms of Innovative Research Award DE SC-0006336 awarded by the Department of Energy.

Technical Field

The present application relates to the field of lithium-ion batteries, and more specifically to the recycling of positive electrode materials of lithium-ion batteries.

Background Art

Lithium-ion batteries power products ranging from cars to smartphones. These batteries can be recharged after many cycles, withstand a wide range of environmental factors, and have a relatively long service life. However, they eventually fail or are discarded before they fail, contributing to a significant and growing waste stream. In response, environmental regulations, industrial standards, and collection services have emerged to promote the recycling of lithium-ion batteries.

Summary of the Invention

This invention discloses an example method for recycling positive electrode materials from lithium-ion batteries. In one example, the positive electrode material is heated under pressure in a concentrated lithium hydroxide solution. After heating, the positive electrode material is separated from the concentrated lithium hydroxide solution. After separation, the positive electrode material is rinsed in an alkaline solution. After rinsing, the positive electrode material is dried and sintered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a method of recycling lithium-ion batteries according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

FIG1 illustrates various aspects of an exemplary method 10 for recycling cathode material from previously used lithium-ion batteries. The illustrated example is somewhat optimized for cathode materials based on nickel-manganese-cobalt (NMC) chemistry, wherein the cathode material includes lithium nickel manganese cobalt oxide (NMC: Li[Ni(1/3)Co(1/3)Mn(1/3)] _O2 having a 1:1:1 Ni:Co:Mn ratio, with many variations available with different metal ratios, such as 6:2:2, 5:2:3, 4:2:2, and others) as the electroactive material. However, all aspects of the illustrated method are also applicable to cathodes of other chemistries. Examples of other cathode materials include, but are not limited to, other materials with nickel in the +3 oxidation state.

At step 12 in method 10, a quantity of previously used positive electrode material is obtained. The positive electrode material can be obtained from any suitable source, such as lithium-ion battery waste or recycling streams. In other embodiments, the positive electrode material can be obtained from general waste or recycling streams. In some cases, the positive electrode material can be obtained from batteries that have exceeded their recommended shelf life or recommended maximum number of recharge cycles.

The acquisition performed at 12 may include disassembling one or more lithium-ion batteries and removing the positive electrode material in the battery. Typically, a lithium-ion battery includes a housing that supports a positive electrode external terminal and a negative electrode external terminal and encloses the positive electrode, the negative electrode, and a non-aqueous electrolyte solution. The positive electrode external terminal can be connected to the positive electrode through the housing, and the negative electrode external terminal can be connected to the negative electrode through the housing. Depending on the battery structure, the housing can be opened by cutting, drilling, and/or prying to expose the positive electrode material, the negative electrode material, and the electrolyte. In some embodiments, the housing can be opened in an atmosphere of low oxygen and/or low humidity. For example, the housing can be opened under a blanket of nitrogen, argon, or carbon dioxide. Such measures can help prevent the negative electrode material (which may include metallic lithium or lithium-embedded carbon) from burning or releasing undesirable heat.

Typically, the extraction process at step 12 includes removing the housing, external terminals, non-aqueous electrolyte, and negative electrode. These components can be recovered separately if desired. Removal of the housing, external terminals, non-aqueous electrolyte, and negative electrode leaves the positive electrode, which can include a positive electrode material supported on an aluminum or other metal/conductive foil substrate. The positive electrode material can also include a substantial amount of a polymer binder (e.g., a fluoropolymer or styrene polybutadiene).

In one embodiment, the positive electrode material may include NMC (LiNi _x Mn _y Co _z O ₂ with various Ni:Mn:Co ratios, such as 1:1:1; 5:3:2; 4:4:2; 6:2:2; 2:6:2). In another embodiment, the positive electrode material may include lithium cobalt oxide (LiCoO ₂ , LCO), lithium manganese oxide (LiMn ₂ O ₄ , LMO), lithium nickel cobalt aluminum oxide (LiNi _x Co _y Al _z O ₂ , NCA), lithium iron phosphate (LiFePO ₄ , LFP), or lithium titanate (Li ₄ Ti ₅ O ₁₂ ). In the form typically recovered from waste or recycling streams, these compounds may be lithium-deficient. In other words, they may contain less than stoichiometric amounts of lithium ions (Li ⁺ ) compared to the originally produced lithium metal oxide material. Therefore, the recycling methods described herein provide the additional benefit of replenishing the lithium content of the recycled positive electrode material.

Continuing with Figure 1, at 14, the supported cathode material is mechanically thrashed in an alkaline medium. This action mechanically separates (i.e., exfoliates) the cathode material from the support, partially separates the cathode material and binder, and pulverizes each of these components to a controllable particle size to facilitate subsequent mechanical and chemical processing (see below). It has been found that thrashing in an alkaline medium (as opposed to an acidic or neutral medium) reduces the decomposition rate of the cathode material during the thrashing process. In some embodiments, the alkaline medium can be a liquid medium, such as an aqueous or non-aqueous solution, in which the cathode material is suspended. In one embodiment, the cathode material is suspended in room temperature water alkalized with lithium hydroxide (LiOH) at a pH in the range of 11.0 to 11.5. This pH range is sufficiently alkaline to retard acid hydrolysis of the NMC serving as the cathode material, but insufficiently alkaline to promote rapid oxidation of the aluminum foil support of the cathode material, which can cause aluminum ions to surge through the system. In other embodiments, different bases, solvents, and pH ranges may be used. In particular, the pH range can be adjusted based on the chemical properties of the cathode material, for example, a more alkaline pH range corresponds to a more alkaline material, and a lower alkaline range corresponds to a less alkaline material. In a particular embodiment, the pH suitable for rinsing is the same as the pH given to the deionized water by the suspended cathode material.

Continuing with reference to FIG1 , as a non-limiting example, the oscillation of the suspended cathode material can be performed in a rotating blade oscillation container, which is roughly similar to a household blender but can accommodate 1 to 10 liters of sample. In a typical operation, 0.5 to 2 kg of a load of cathode material is oscillated in 1 liter of alkaline water for 5 minutes. Naturally, other sample sizes and oscillation times are also contemplated.

Various solids from the loaded positive electrode material are collected from the shaken slurry at 16. The solids may be collected by, for example, gravity filtration, pressure filtration, vacuum filtration, and/or centrifugation.

At step 18, the collected solids are rinsed with a liquid to remove the alkaline medium used during the shaking and any electrolyte (salts and non-aqueous solvent) remaining on the loaded positive electrode material prior to shaking. Rinsing can be performed in the same filtration or centrifugation apparatus used to collect the solids. In some embodiments, an organic solvent can be used for rinsing. It is preferred that the selected solvent be partially or fully miscible with water so that the rinsing process also removes water entrained in the collected solids (from the alkaline shaking medium). It is also preferred that the solvent be recoverable from the rinse liquid, harmless to workers and the environment, and/or suitable for inexpensive disposal that complies with applicable regulations. Acetone, ethanol, and some other alcohols are good candidates for rinse solvents due to their miscibility with water, relatively low toxicity, and ability to dissolve non-aqueous electrolyte solvents and salts (e.g., lithium hexafluorophosphate and its decomposition products, such as LiF and various phosphates; lithium triflate; ethylene carbonate; diethyl carbonate, etc.). Acetone and ethanol can also be recovered from the rinse liquid by vacuum distillation.

Because acetone is a good solvent for organics but a relatively poor solvent for LiOH, it has additional attractive properties as a rinse solvent. More specifically, various organic compounds (e.g., low molecular weight polymers and fluoropolymers, plasticizers, etc.) may be present in the binder used to adhere the cathode material to the substrate. Washing with acetone dissolves or solubilizes at least some of these components, allowing them to be rinsed away and excluded from subsequent processing. This improves the purity of the recovered cathode material. Furthermore, in embodiments where the agitation is performed with alkalized water containing lithium hydroxide (LiOH), the low solubility of LiOH in acetone is beneficial. Here, a small amount of LiOH remains on the rinsed solids, which can inhibit acid hydrolysis of the cathode material during the recovery process.

In other embodiments, the collected solids can be rinsed in an aqueous solution having an appropriate pH (e.g., an aqueous LiOH solution having a pH of 11.0-11.5) in various organic solvents. Supercritical carbon dioxide can also be used for rinsing. Although the rinsing step at 18 has advantages, it is not required and can be omitted in some embodiments.

At 20, the rinsed solid is dried to remove adsorbed water and residual rinse solvent. In various embodiments contemplated herein, drying can be performed in a vacuum or under a flow of dehumidified (e.g., heated) air or other dry gas such as nitrogen, argon, or carbon dioxide. In one embodiment, the rinsed solid is dried in a vacuum oven at 140°C.

At 22, the dried solid is mechanically ground. The purpose of this grinding step is to reduce the particle size of the positive electrode material, in particular to improve the yield in subsequent screening. In one non-limiting example, a ball mill can be used for grinding. In a typical operation, 60 grams of dry solid and 30# agate balls with a mixed diameter of 0.5 to 1 cm are added to a 400 ml capacity ball mill. For example, the ball mill can be run at 50 Hz for 3 to 5 minutes. It should be noted that the grinding performed at 22 may inappropriately reduce some of the aluminum substrate to a particle size comparable to that of the positive electrode material, which may reduce the effectiveness of subsequent purification by size selection. Omitting or shortening the grinding step or modifying the ball mill frequency can improve product purity at the expense of reduced yield.

At 24, the ground solid is size-selected using one or more fine screens so that the positive electrode material can be separated from the substrate sheets, binder, and steel scraps produced by cutting the battery apart during the acquisition step. In one embodiment, the positive electrode material selected for further processing is the portion that passes through a 38 to 45 micron sieve, preferably a 38 micron sieve. This portion is subjected to a second grinding step at 22' to further reduce its particle size. Without wishing to be bound by theory, the second grinding step is believed to improve the efficiency of the subsequent hydrothermal treatment to restore the stoichiometric lithium content of the recovered positive electrode material. Of course, other orders of grinding and size exclusion are also contemplated. In some embodiments, a fine filtration step performed in an alkalized liquid medium can be used instead of screening.

At 28, the twice-milled solid is introduced into an autoclave along with a concentrated aqueous LiOH solution. The hydrothermal treatment can help restore the stoichiometric lithium content of the positive electrode material, for example, by replacing any foreign cations (i.e., impurities) or possible dislocated cations (i.e., nickel ions that can migrate to lithium sites in the crystal lattice). In one embodiment, 1 liter of 24% LiOH can be used for each kilogram of positive electrode material. It should be noted that at certain ambient temperatures, this concentration of LiOH exceeds saturation. The contents of the autoclave can be raised from an ambient temperature of 250°C to 275°C at a rate of 5°C/minute and maintained at this temperature for 12 to 14 hours. Higher temperatures have been found to reduce yields by promoting undesirable side reactions involving residual binders. In other examples, any other suitable lithium ion solution other than lithium hydroxide solution can be used in the hydrothermal treatment.

At 16', the cooled, hydrothermally treated solids are collected and, at 30, rinsed to remove excess LiOH. Experiments have shown that the properties of the recovered cathode material are sensitive to the rinsing method used at this stage of the process. In particular, neutral to acidic conditions appear to be avoided to optimize the desired electrochemical properties (e.g., capacity and current capacity) of the cathode material. Without wishing to be bound by theory, susceptibility to acid hydrolysis may be particularly high at this stage, since the binder has already been largely eliminated. Therefore, the collected solids can be rinsed with water alkalized with LiOH to a pH within the same range as used in the rinse step 18 (e.g., pH 11.0 to 11.5 for NMC). Alternatively, the collected solids can be rinsed with less alkaline or even deionized water, while the pH of the filtrate is continuously monitored at 32. Other suitable solvents for rinsing may include, but are not limited to, non-aqueous solvents, such as liquid carbon dioxide, supercritical carbon dioxide, methanol, ethanol, isopropanol, tert-butanol, n-butanol, ethylene glycol, polyethylene glycol, and/or solutions thereof. Rinsing is terminated when the pH of the filtrate falls within the desired range. For a particular 500 gram batch of cathode material, a total of 4 liters of wash water may need to be used before the pH drops to the target range. In another embodiment, 4 liters of aqueous LiOH solution within the desired pH range may be used.

At 20', the rinsed, hydrothermally treated solid is vacuum dried at 150 to 160°C, and at 22', the solid is ground a third time to the desired particle size. Without wishing to be bound by theory, grinding at this stage is believed to improve the efficiency of subsequent sintering. At 36, the solid after the third grinding is sintered under a flow of air or oxygen. In one embodiment, a tube furnace can be used for sintering. As a non-limiting example, the temperature of the sample in the furnace can be increased from ambient temperature to 900°C at a rate of 2 to 3°C/minute and maintained at this temperature for 8 hours. Sintering can help increase the grain size of the positive electrode material and convert it into an allotrope that is more stable at higher temperatures. Experiments have shown that high-temperature allotropes of NMC have better performance in lithium-ion batteries. The final stage of sintering includes rapid cooling of the sample. In one embodiment, as a non-limiting example, the sample is cooled from 900°C to ambient temperature at a rate of about 50°C/minute. This cooling rate can help "lock" the cathode material grains into the most stable allotrope at high temperatures and prevent them from reversing to a form that is more stable at lower temperatures. The use of oxygen during the sintering process can help oxidize the nickel ions in the NMC formulation.

In one embodiment, rapid cooling of the sintered sample can be performed under a flow of carbon dioxide allowed into the furnace. The carbon dioxide converts lithium oxide (derived from excess LiOH) into lithium _carbonate ( _Li2CO3 ). Preliminary evidence suggests that small amounts _{of Li2CO3} introduced with the cathode material can improve the performance of lithium-ion batteries. For example, converting excess LiOH into _the less hygroscopic _Li2CO3 can help keep the cathode material drier during storage and transportation. At 22''', the sintered cathode material is re-milled to provide a particle size particularly suitable for application to a new cathode support.

Without departing from the scope of the present disclosure, some of the processing steps described and/or illustrated herein may be omitted in some embodiments. Likewise, the order of the processing steps indicated may not always be required to achieve the desired results, but is provided for ease of illustration and description. Depending on the specific strategy used, one or more of the actions, functions, or operations shown may be repeated. It should be understood that the articles, systems, and methods described above are embodiments of the present disclosure—non-limiting examples, for which various variations and extensions are also contemplated. The present disclosure also includes all novel and non-obvious combinations and sub-combinations of the above-described articles, systems, and methods, and any and all equivalents thereof.

Claims (22)

1. A method for recycling positive electrode materials from lithium-ion batteries, the method comprising: A cathode material, including a nickel-manganese-cobalt cathode material, is heated under pressure in a solution containing lithium ions. After heating, the cathode material is separated from the solution containing lithium ions; After separation, the positive electrode material is rinsed in an alkaline liquid; and After rinsing, the cathode material is dried and sintered. 2. The method according to claim 1, wherein rinsing the positive electrode material comprises rinsing with a solution or buffer solution of alkaline pH. 3. The method according to claim 1, wherein rinsing the positive electrode material comprises rinsing with a solution of water and lithium hydroxide. 4. The method according to claim 1, wherein rinsing the positive electrode material comprises rinsing with one or more non-aqueous solvents selected from methanol, ethanol, isopropanol, tert-butanol, n-butanol, ethylene glycol and polyethylene glycol, or a solution containing said non-aqueous solvent. 5. The method according to claim 1, characterized in that it further includes sieving the positive electrode material before heating to separate the positive electrode material from other solids. 6. The method according to claim 5, characterized in that it further comprises, before sieving the positive electrode material, agitating the positive electrode material in one or more of an alkaline medium, a non-aqueous solvent, or in a solution containing a non-aqueous solvent, wherein the non-aqueous solvent comprises one or more of methanol, ethanol, isopropanol, tert-butanol, n-butanol, ethylene glycol, polyvinyl glycol, liquid carbon dioxide, and supercritical carbon dioxide. 7. The method according to claim 6, wherein the oscillating of the positive electrode material comprises oscillating in a lithium hydroxide solution. 8. The method according to claim 6 or 7, characterized in that, after oscillating the positive electrode material and before sieving, it further includes rinsing the positive electrode material in acetone and/or ethanol to remove the alkaline medium used during oscillation and to remove the electrolyte retained on the loaded positive electrode material before oscillation, said electrolyte comprising ethylene carbonate and/or diethyl carbonate. 9. The method according to claim 1, characterized in that it further comprises, after sintering, cooling the cathode material in carbon dioxide to convert residual lithium oxide in the cathode material into lithium carbonate. 10. The method according to claim 1, characterized in that it further comprises, after drying, grinding the positive electrode material to reduce the particle size of the positive electrode material. 11. The method according to claim 1, wherein the lithium-ion-containing solution comprises a lithium hydroxide solution. 12. A method for recycling positive electrode material from lithium-ion batteries, the method comprising: A cathode material, including a nickel-manganese-cobalt cathode material, is heated under pressure in a lithium hydroxide solution. After heating, the positive electrode material is separated from the lithium hydroxide solution; After separation, the positive electrode material is rinsed in an alkaline liquid; and After rinsing, the cathode material is dried and sintered. 13. The method according to claim 12, wherein rinsing the positive electrode material comprises rinsing with a solution of water and lithium hydroxide. 14. The method according to claim 12, wherein rinsing the positive electrode material comprises rinsing with one or more non-aqueous solvents selected from methanol, ethanol, isopropanol, tert-butanol, n-butanol, ethylene glycol, polyethylene glycol, liquid carbon dioxide, and supercritical carbon dioxide, or a solution containing said non-aqueous solvent. 15. The method according to claim 12, characterized in that it further comprises sieving the positive electrode material before heating to separate the positive electrode material from other solids. 16. The method according to claim 15, characterized in that it further comprises, before sieving the positive electrode material, oscillating the positive electrode material in an alkaline medium. 17. The method according to claim 16, wherein the oscillating of the positive electrode material comprises oscillating in a lithium hydroxide solution. 18. The method according to claim 16 or 17, characterized in that, after oscillating the positive electrode material and before sieving, it further includes rinsing the positive electrode material in acetone and/or ethanol to remove the alkaline medium used during oscillation and to remove the electrolyte retained on the loaded positive electrode material before oscillation, said electrolyte comprising ethylene carbonate and/or diethyl carbonate. 19. The method according to claim 12, further comprising, after sintering, cooling the cathode material in carbon dioxide to convert residual lithium oxide in the cathode material into lithium carbonate. 20. The method according to claim 12, characterized in that it further comprises, after drying, grinding the positive electrode material to reduce the particle size of the positive electrode material. 21. A method for recycling positive electrode material from lithium-ion batteries, the method comprising: A positive electrode material is vibrated in an alkaline medium, wherein the positive electrode material includes a nickel-manganese-cobalt positive electrode material; The positive electrode material is collected through filtration. The cathode material is heated under pressure in a lithium hydroxide solution; After heating, the positive electrode material is separated from the lithium hydroxide solution; After separation, the positive electrode material is rinsed in an alkaline liquid; and After rinsing, the cathode material is dried and sintered. 22. The method according to claim 21, characterized in that it further comprises, after sintering, cooling the cathode material in carbon dioxide to convert residual lithium oxide in the cathode material into lithium carbonate.