Recycling of lithium ion cells

Abstract

Methods are disclosed for recycling one or more cells (e.g., lithium-ion cells or lithium polymer cells), as well as batteries utilizing the cell(s), which methods provide a simple, effective, and safe protocol for accessing electrodes within the cell(s) by dissolution of at least some of the cell housing, such as a metal can or pouch. The methods comprise contacting the cell(s) with an aqueous electrolyte solution (e.g., a salt solution, an acid, or a base) to cause at least partial corrosion / dissolution and preferably facilitate removal of electrode assemblies contained within the cells. Representative methods are furthermore preferably accompanied by the discharge of the cell(s), such as multiple cells of a battery, in a rapid and cost-effective manner.

Description

RECYCLING OF LITHIUM ION CELLSCROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 522,450, filed June 22, 2023, which is hereby incorporated by reference in its entirety.FIELD OF THE INVENTION

[0002] Aspects of the invention relate to methods for recycling of cells, including lithium-ion cells, by contact with an aqueous electrolyte solution (e.g., of a salt, an acid, or a base) to cause dissolution and thereby facilitate removal of the electrode assembly.DESCRIPTION OF RELATED ART

[0003] Batteries having a range of capacities, governed by the number of connected battery cells, are widely used as power supplies for diverse applications. For example, a single cell may be used in a pack for portable electronic devices such as cellular phones, plasma display panels, notebook computers, cameras, etc. High-capacity batteries that include a pack having multiple connected battery cells are used, for example, as power supplies for hybrid vehicles and also in stationary grid energy storage. Lithium cells, including lithium-ion cells (e.g., in a metal prismatic format) and lithium polymer cells (e.g., in a pouch prismatic format), which are characterized according to the type of charge-transporting electrolyte contained in these cells, are particularly advantageous in terms of their relatively high nominal voltage (e.g., 3.3-3.8 V) and energy density per weight, compared to other battery types, such as nickelcadmium and nickel hydride batteries.

[0004] Although the recycling of batteries is a common practice and highly desired from an economic perspective, most battery recycling currently involves lead acid batteries according to a process that has been optimized over several decades. With the advent of lithium-ion cells and batteries and the prolific use of this chemistry for electricity generation, the need to recycle these has become imperative not only for environmental purposes but also for recovery of the expensive metals. However, lithium-ion cells and batteries often have flammable charge-transporting electrolytes that pose flammability and explosion risks, for example in the case of pressurization, due to damage that leads to internal short circuits. Also, improperly recycled batteries can create toxic waste from the metals used. Significant safety concerns arise in recycling facilities, in which lithium-ion cells and batteries are prone to thermal runaway, leading to fires, if not safely discharged before crushing. Furthermore,in lead acid battery recycling facilities in which lithium-ion batteries are inadvertently mixed, significant fire damage has resulted from the crushing of lithium-ion cells and batteries together with lead acid batteries.

[0005] To appropriately address these significant safety hazards, it is conventionally accepted that every lithium-ion battery or cell must be discharged using test equipment and / or a resistive load, followed by removing the internal electrodes to be recycled. This is a time-consuming and costly proposition. For example, the cell housing, which may be in the form of a cylindrical or prismatic metal can, or otherwise an aluminized plastic pouch, must be opened to remove the electrodes from inside the can or pouch. Prior to this, full discharge, for example to a measured voltage between 0 and 1 volt, is necessary to ensure that safe cutting and / or shredding can proceed. Accounting for each individual cell, the discharging and opening steps of the recycling process demand significant operating and capital requirements, such as test equipment channels. Moreover, discharging at the battery level does not equate to full discharge at the cell level, as batteries of lithium-ion cells are fitted with a battery management system that will prevent them from over-discharge. The cells must therefore be removed from the battery configuration and confirmed to be fully discharged, before being further processed for recycling. If the discharge is incomplete, or possibly even despite a complete discharge, the risk of a fire with cells having the lithium-ion chemistry is not totally eliminated, since the contact between a cathode and anode in the presence of the chargetransporting electrolyte, particularly in the case of a liquid, within the cells can create a short circuit leading to thermal runaway and fire.

[0006] The present state of the art would therefore benefit from improvements in methods for recycling cells, such as lithium-ion cells as well as batteries incorporating these cells, which can mitigate or possibly eliminate the problems and / or complexities noted above.SUMMARY OF THE INVENTION

[0007] Aspects of the invention are associated with the discovery of methods for recycling one or more cells (e.g., lithium-ion cells or lithium polymer cells), as well as batteries utilizing the cell(s), which methods provide a simple, effective, and safe protocol for accessing electrodes, or the electrode assembly, within the cell(s) by dissolution of at least some of the cell housing, such as a metal can or pouch. Representative methods are furthermore preferably accompanied by the discharge of the cell(s), such as multiple cells of a battery, in a rapid and cost-effective manner. The inventive methods may differ in one or more respects fromconventional techniques in which salt (e.g., NaCl) solutions are used to cause battery discharge, but with only minimal or no corrosion. Such techniques were namely developed in the absence of any recognition of the potential benefits associated with cell dissolution, in terms of facilitating electrode assembly removal and thereby the overall recycling process. Differences may reside, for example, in the inventive methods having (i) a greater extent of dissolution (e.g., determined by weight loss), and / or (ii) operating parameters associated with such greater extent of dissolution. Such parameters may include, for example, (a) increased total immersion / dissolution time; (b) increased immersion / dis solution time, beyond that needed to achieve a given level of discharge; (c) increased corrosivity of the aqueous electrolyte solution used for cell / battery discharge and dissolution (e.g., based on a lower or higher pH, the use of acids or bases, etc.); (d) certain processing steps (e.g., initial removal of outer layers or penetration to expose underlying layers, recovery of dissolved metals, etc.) and / or (e) certain process evaluations / measurements being made (e.g., weight, or weight loss, of a cell / battery; concentration(s) of metal(s) in the aqueous electrolyte solution; pH and / or conductivity of this solution; end point determination based on visual inspection / photographs, such as to ascertain ease of electrode assembly removal, etc.).

[0008] According to some embodiments, the objective of a given method may be to maximize cell / battery corrosion for the removal of internal components, such as the electrode assembly, optionally in conjunction with discharge. In the case of cylindrical lithium-ion cells (e.g., 18650 model cells), this electrode assembly may be in the form of a “jellyroll” or “flat sheet” configuration of a layered positive electrode, separator, negative electrode, and separator, with these layers being rolled into the cylindrical form (to obtain a spiral of the layers) or being stacked in a prismatic form. The rapid removal of the electrode assembly, according to methods described herein, is likewise facilitated in the case of lithium-ion cells or lithium polymer cells having other forms, such as pouch forms.

[0009] Particular aspects are associated with methods for performing at least partial dissolution of a housing (e.g., a cylindrical or prismatic can, or pouch) of a cell, and particularly a lithium-ion cell or lithium polymer cell, or otherwise at least partial dissolution of a metallic layer of the housing. Such dissolution, of at least a portion of this housing or container, can facilitate the efficient removal of electrodes, and optionally other components of the electrode assembly of the cell, for recycling. Advantageously, these methods can likewise provide a safe discharge of the cell, or plurality of cells, as also needed for recycling. This recycling may involve the re-use of expensive metals (e.g., Li, Co, Ni, Mn, Al, Cu, Fe, etc.), which may be recoveredfrom the electrodes, housing, or other components of the cell, for example following the removal of the electrode assembly. In view of the occurrence of at least some dissolution of the cell, this recycling may also involve the recovery of these and other metals in dissolved form, from the aqueous electrolyte solution, or as other types of corrosion products in this solution. For example, in the case of recovering dissolved iron, this metal may be converted to a suitable salt, such as iron phosphate, that may be used as a lithium-ion cathode material. Other possible salts include ferrous / ferric carbonates, ferrous / ferric chlorides, ferrous / ferric sulphates, etc., which can be applied in any of a number of industrial chemical applications.

[0010] These and other embodiments, aspects, and advantages relating to the present invention are apparent from the following Detailed Description.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] A more complete understanding of the exemplary embodiments of the present invention and the advantages thereof may be acquired by referring to the following description in consideration of the accompanying figures.

[0012] FIG. 1 illustrates the voltage behavior over time of (A) cylindrical metal can 18650 cells and (B) pouch cells, immersed in various aqueous electrolyte solutions. Pouch cells were scored prior to placement in the solutions.

[0013] FIG. 2 illustrates the voltage behavior over time of cylindrical metal can cells, immersed in NaCl solutions of 1 wt-%, 5 wt-%, and 10 wt-% concentration.

[0014] FIG. 3 illustrates the voltage behavior over time of cylindrical metal can cells, immersed in Na2COa solutions of 1 wt-%, 5 wt-%, and 10 wt-% concentration.

[0015] FIG. 4 illustrates the voltage behavior over time of cylindrical metal can cells, immersed in HC1 solutions of 1 wt-% and 5 wt-% concentration.

[0016] FIG. 5 illustrates the voltage behavior over time of cylindrical metal can cells, immersed in NaOH solutions of 1 wt-% and 5 wt-% concentration.DETAILED DESCRIPTION

[0017] The expression “wt-%” is used herein to designate weight percentage, and the expression “wt-ppm” is used to designate weight parts per million.

[0018] Embodiments of the invention are directed to methods for recycling one or more cells, with these methods being particularly applicable to cells used in lithium-ion batteries (also referredto as “Li-ion batteries”), which are types of rechargeable batteries based on the reversible reduction of lithium ions for electrical energy storage and release. Examples of such batteries are also known as “secondary batteries,” which differ from dry cells that cannot be recharged. The cells can include a “lithium-ion cell” (also referred to as an “Li-ion cell”), which encompass cells used in lithium-ion batteries generally and that contain electrode assemblies having charge-transporting electrolytes in any form, such as a liquid (e.g., organic solvent) form or a solid (e.g., ceramic) form. The terms “lithium-polymer cell” (also referred to as “Li polymer cell”) and “lithium-ion polymer cell” (as referred to as “Li-ion polymer cell”) more specifically refer to a lithium-ion cell containing an electrode assembly with a polymer charge-transporting electrolyte, such as a cell having a flat or pouch configuration that may be referred to as a “pouch-type” lithium cell. These terms, namely “lithium-polymer cell” (or “Li polymer cell”) and “lithium-ion polymer cell” (or “Li-ion polymer cell”) consistent with their usage in the art, likewise encompass pouch-type lithium cells having a liquid or solid- state charge-transporting electrolyte.

[0019] As alternatives to the housing of a cell being in a pouch form, this housing may be in any of a variety of forms, including conventional forms, such as in the form of cylinder having certain dimensions depending on the particular use of the cell. A housing in cylindrical form may be referred to as a “cylindrical can,” in the case of a particular “can-type” lithium cell, with specific commercial examples of cylindrical can-type lithium cells being 18650, 21700, or 4680 model Li-ion cells. As an alternative to a cylindrical shape for accommodating the electrode assembly, a can-type lithium cell may have a housing, typically with a rigid structure, of a different shape for this purpose, for example in the case of a prismatic lithium cell. In this regard, prismatic lithium cells include not only those of a can-type, but also those having a pouch form. The housing of a can-type lithium cell (e.g., 18650 model Li-ion cell), regardless of the particular form (e.g., cylindrical or prismatic), typically comprises steel, such as in the case of stainless steel, or aluminum, such as in the case of an aluminum alloy. The housing (or outer casing) of a pouch-type lithium cell typically comprises plasticized aluminum, having a thin layer of aluminum with at least one adjacent layer of plastic. Lor example, the aluminum layer may be sandwiched between two exterior plastic layers that prevent direct contacting of the aluminum with the exterior environment or the cell internal components (e.g., the charge-transporting electrolyte). As opposed to a can-type lithium cell, the housing of a pouch-type lithium cell is usually flexible.

[0020] The electrode assembly contained within the cell housing (e.g., can or pouch) generally includes a positive electrode plate, and negative electrode plate, and a separator interposed between these plates. Cells having a housing in the form of a cylindrical can are normally produced with the electrode assembly formed into a characteristic “jellyroll,” whereby the positive electrode, separator, negative electrode, and separator are rolled into a single long, layered spool. Otherwise, the electrodes, for example when contained in a metallic prismatic housing or pouch, can be in a jellyroll or a stacked configuration. Different electrode configurations have different characteristics in terms of their speed of production and tendency to form substantial temperature gradients. The electrode plates, in any event, are in electrical communication with positive and negative terminals of the cells. In the case of a cell having a cylindrical housing, for example, the cylindrical can and its contents (electrode assembly and charge-transporting electrolyte) are typically sealed with a cap assembly that includes one terminal (e.g., the positive terminal). This assembly and terminal are insulated from the can by an insulating gasket, whereas the can itself may serve as the other terminal (e.g., the negative terminal). The configuration of a particular cell and its components of a housing, electrode assembly, charge-transporting electrolyte, and terminals is described in US 2009 / 0117451, hereby incorporated by reference with respect to this configuration.

[0021] Whereas methods described herein are applicable to recycling of cells, they are likewise applicable to the recycling of batteries (e.g., Li-ion batteries) comprising a plurality or collection of cells in electrical communication.

[0022] Methods described herein for recycling a cell, a plurality of cells (e.g., subjected to dissolution simultaneously), a battery, or a plurality of batteries (e.g., subjected to dissolution simultaneously), are characterized by a step of contacting under dissolution conditions. To the extent that the disclosed and claimed methods “comprise” this step, these methods do not preclude further steps that may be used in the separation, recovery, and / or reuse of materials, according to any specific recycling protocol. For example, following the contacting under dissolution conditions, representative methods may further comprise opening, or further opening (e.g., in the case of the contacting resulting in at least partial opening) of the housing, such as by physical deformation (e.g., cutting, crushing, shredding, etc.) in order to access, separate, and / or remove the electrode assembly. In this regard, methods for recycling, as described herein, may optionally, according to some embodiments, be characterized as methods for preparing such a cell, a plurality of cells, a battery, or a plurality of batteries, forthe recovery and reuse of their components (and / or their dissolved components), or otherwise preparing such a cell, a plurality of cells, a battery, or a plurality of batteries, for recycling.

[0023] According to representative embodiments, the invention is directed to a method for recycling at least one cell and / or at least one battery, with this method comprising contacting the cell(s) / battery(ies) with an aqueous electrolyte solution, which is different from the chargetransporting electrolyte used within the cell(s) / battery(ies). The at least one cell and / or at least one battery comprises a housing having an electrode assembly disposed therein, and the housing comprises a metallic layer (e.g., a steel layer, such as in the case of certain can-type lithium cells, or an aluminum layer, such as in the case of certain pouch-type lithium cells). The contacting is performed under dissolution conditions effective to dissolve at least a portion of the metallic layer. In this manner, methods described and claimed herein are distinguishable over the use of electrolyte solutions merely for the purpose of electrically discharging cells and / or batteries. For example, methods described and claimed herein generally involve exposure to electrolyte solutions of a higher corrosivity and / or for a longer time period, in order to achieve effective dissolution, such as to an extent needed to facilitate removal of the electrode assembly.

[0024] According to more particular embodiments, the dissolution conditions may be effective to dissolve, for example, at least about 5%, at least about 10%, at least about 20%, at least about 30%, at least about 40%, or at least about 50%, by weight of the metallic layer (or by weight of the metal in the housing). In some embodiments, optionally in combination with any of these minimum amounts of dissolution of the metallic layer, the dissolution conditions may dissolve at most about 95%, at most about 90%, at most about 85%, at least about 80%, at most about 75%, or at most about 70%, by weight of the metallic layer (or by weight of the metal in the housing). Alternatively or in combination, such dissolution conditions may be effective to dissolve at least about 0.2%, at least about 0.5%, at least about 1%, at least about 3%, at least about 5%, or at least about 10%, by weight, based on the entire weight of the at least one cell and / or the at least one battery. In some embodiments, optionally in combination with any of these minimum amounts of dissolution of the at least one cell and / or the at least one battery, the dissolution conditions may dissolve at most about 50%, at most about 40%, at most about 35%, at most about 30%, at most about 25%, or at most about 20%, by weight of the at least one cell and / or the at least one battery.

[0025] In some embodiments, effective dissolution conditions may be readily determined, such as by measurement and / or by visual observation, based on the condition of a positive terminal ofthe cell, which may be more susceptible to corrosion by the aqueous electrolyte solution, relative to other components of the cell. For example, optionally in combination with any amounts of dissolution of (a) the metallic layer (or metal in the housing) and / or (b) the at least one cell and / or the at least one battery, as described above, the dissolution conditions may be effective to dissolve at least about 30%, at least about 50%, at least about 75%, or at least about 85%, at least about 90%, or at least about 95%, by weight of the positive terminal of the cell. In some embodiments, the dissolution conditions may be effective to completely dissolve, or to separate, the positive terminal, thereby advantageously facilitating removal of internal components (e.g., the electrode assembly).

[0026] Specific forms of the housing of a given cell or battery include the form of a cylindrical can or a prismatic can, and also include the form of a pouch, as described above. In the case of a cylindrical can or a prismatic can, the housing, or metallic layer of the housing, may comprise steel. For example, the housing may be in the form of a cylindrical can or prismatic can, with the housing including a steel layer having a plastic outer layer, such as a label, disposed thereon. In order to promote dissolution, representative methods may comprise, prior to contacting of the at least one cell and / or the at least one battery with the aqueous electrolyte solution, partially or completely removing an outer plastic layer (e.g., a label) of the cylindrical can or prismatic can, thereby increasing exposure of the metallic layer, such as a steel layer, of the housing to the aqueous electrolyte solution. Preferably, any outer plastic layer is completely removed.

[0027] In the case of the housing being in the form of a pouch, the metallic layer (e.g., an aluminum layer) may have a plastic outer layer, as well as a plastic inner layer, such that these layers surround the metallic layer, as described above. In order to promote dissolution, representative methods may comprise, prior to contacting of the at least one cell and / or the at least one battery with the aqueous electrolyte solution, penetrating (e.g., scoring) the outer plastic layer to increase exposure of the metallic layer to the aqueous electrolyte solution. Regardless of the particular form of the housing, representative methods may comprise any suitable step to cause direct exposure of at least a portion of the metallic layer to the aqueous electrolyte solution. This may include, prior to the contacting with such solution, and / or over the course of this contacting (e.g., following removal from the solution and preceding reimmersion), penetrating the outer plastic layer such as by pricking to form a pinhole, scratching, scraping, peeling, and / or removing all or part of the outer plastic layer (e.g., label).

[0028] The step of contacting of the least one cell and / or at least one battery (or exposed metallic layer of the least one cell and / or at least one battery) may be performed by partial or complete immersion in the aqueous electrolyte solution. Preferably the least one cell and / or at least one battery is / are completely immersed. The contacting may be performed batchwise, such as in the case of the cell(s) / battery(ies) being maintained in a fixed volume of solution, or the contacting may be performed continuously, with the cell(s) / battery(ies) being subjected to the solution under flowing conditions. A combination of batchwise and continuous operation is also possible, for example, by utilizing a vessel for maintaining the cell(s) / battery(ies) in contact with the solution, but with the periodic or continuous addition of fresh aqueous electrolyte solution to limit the accumulation of corrosion products and / or limit the loss of solution strength. The aqueous electrolyte solution may be a solution of a salt, with particular examples including a chloride salt, a carbonate salt, a bicarbonate salt, a nitrate salt, a phosphate salt, or a sulfate salt, with alkali metal or alkaline earth metal salts (e.g., sodium, potassium, magnesium, or calcium salts) of any of these anions being preferred. Particularly preferred salts, used in aqueous electrolyte solutions, include NaCl, Na2COa, and NaHCOa. Other aqueous electrolyte solutions include acids, such as HC1, H2SO4, and HNO3, with these acid solutions preferably having a pH of less than about 6, less than about 5, less than about 4, or less than about 3, such as in the range from about 0 to about 3. Further aqueous electrolyte solutions include bases such as hydroxides, with NaOH and KOH being representative examples. In this case, such base solutions may preferably have a pH of greater than about 8, greater than about 9, greater than about 10, or greater than about 11, such as in the range from about 11 to about 14. Any salt, acid, or base may be present in the aqueous electrolyte solution in a suitable amount up to its solubility, and in preferred embodiments, the salt, acid, or base is present in an amount generally from about 0.1 wt-% to about 20 wt-%, typically from about 0.5 wt-% to about 15 wt-%, and often from about 1 wt- % to about 10 wt-%, such as from about 1 wt-% to about 5 wt-% or from about 5 wt-% to about 10 wt-%. As a dissolution condition, the aqueous electrolyte solution may be maintained at nearly room temperature, such as in a temperature range from about 10°C to about 25 °C, but in some cases elevated temperature, such as in the range from about 20°C to about 75°C, from about 30°C to about 75°C, or from about 30°C to about 50°C, may be used to increase the corrosion / dissolution rate.

[0029] As noted above, particular aspects of the invention relate to certain advantages attained from at least partially dissolving or corroding a cell, in terms of its overall regeneration that mayinclude subsequent material recovery. Typically, a requisite degree of dissolution, or effective dissolution of at least a portion of the metallic layer of the cell or battery housing, may require contacting (e.g., immersion) of the cell or battery for a time longer than needed for merely causing its substantial discharge. For example, according to some embodiments, representative dissolution conditions may include a contacting time (either under stagnant or flowing conditions) of at least about 3 hours, at least about 6 hours, at least about 12 hours, at least about 24 hours, or at least about 72 hours, beyond discharging the cell to a voltage (z.e., its open circuit voltage or OCV) that is below a given threshold voltage. For example, this threshold voltage may be, according to any of these embodiments, 3 volts, 2.5 volts, 2 volts, 1.5 volts, 1 volt, or 0.5 volts. Accordingly, certain dissolution conditions may include a contacting time, for example, of at least about 12 hours, beyond discharging the cell to a voltage of 1 volt or less, with various other combinations of contacting times and threshold voltages being possible. In some embodiments, the initial state of charge (SOC) of the cell or battery, prior to the contacting, may be characteristic of a used cell or battery, such as being in a range from about 30% to about 70%, or from about 40% to about 60%, with 50% SOC being an exemplary value. The initial voltage of the cell (e.g., when present alone or in a battery of multiple cells), prior to the contacting, may be from about 2.5 to about 5 volts, or from about 3 volts to about 4 volts, with 3.6 volts being an exemplary value.

[0030] In any of these embodiments, the contacting time may be continuous or non-continuous, such as in the case of the cell or battery being withdrawn from the aqueous electrolyte solution intermittently (e.g., periodically) for visual analysis, voltage measurement, sampling, weighing, etc. In the case of non-continuous contacting, the contacting time herein refers to the total time of the battery or cell being in contact with aqueous electrolyte solution. In representative embodiments, the continuous or non-continuous contacting time may be at least about 48 hours, at least about 72 hours, at least about 96 hours, or at least about 120 hours. This continuous or non-continuous contacting time may, optionally in combination with any of these minimum contacting times, be at most about 240 hours, at most about 216 hours, at most about 192 hours, or at most about 168 hours. In the case of non-continuous contacting, the cell or battery may be intermittently (e.g., periodically) withdrawn or removed from contact with the aqueous electrolyte solution at one or more suitable times, or at predetermined times, over the course of the contacting, such as at various intervals (e.g., every 2 hours, every 4 hours, every 8 hours, every 12 hours, every 24 hours). The cell or battery may be, for example, visually inspected or photographed, measured for its voltage(e.g., OCV), sampled, and / or weighed, one or more times over the course of the contacting, such as from one to ten times, or from one to five times, thereby interrupting the total contacting time.

[0031] In representative methods, the aqueous electrolyte solution may be analyzed continuously or intermittently (e.g., periodically) over the course of the contacting, for example according to any of the intervals described above, and / or for any number of times as described above, with respect to withdrawing or removing the cell or battery for various purposes. Representative analyses that may be conducted one or more times over the course of the contacting include pH analysis, conductivity analysis, and / or metals analysis. For example, inductively coupled plasma mass spectroscopy (ICP-MS) or inductively coupled plasma optical emission spectroscopy (ICP-OES) are analytical techniques that may be used to determine trace amounts of metals in the aqueous electrolyte solution, resulting from corrosion / dissolution of the battery or cell. These metals may include any one or more of Li, Co, Ni, Mn, Al, Cu, and Fe. According to some embodiments, methods may comprise recovering any one or more of these metals from the aqueous electrolyte solution. Such metals may concentrate in a froth or foam, formed at the top of this solution; may be uniformly concentrated in this solution (e.g., as dissolved ions); and / or may concentrate in a bottoms sediment that forms in this solution. Recovering the metals may involve precipitation (e.g., forming a precipitate of an insoluble form of the metal or concentrating the metals), the use of an ion-exchange resin or other suitable extraction medium, filtration, etc. In view of the possibility for recovery of valuable metals, including lithium, that may result from dissolution of the cell or battery, the overall economics associated with recycling may be improved.

[0032] As described above, the contacting step, which results in at least partial dissolution of the cell or battery over the contacting time, can reduce the subsequent requirements for physical removal of the electrode assembly, as part of a recycling process. For example, the amount of cutting and / or shredding, and / or the degree of physical force needed, may be reduced. In some embodiments, the dissolution conditions may be effective for removal of the electrode assembly, without cutting the housing, for example the method may further comprise removing the electrode assembly without cutting or otherwise destroying the housing, as made possible by a sufficient degree of corrosion / dissolution.

[0033] Representative methods may comprise contacting a plurality of cells and / or batteries simultaneously, such as in a suitable contacting vessel (e.g., an open vat or a closed container, depending on whether overhead vapors should be contained) having properties (e.g., size,strength, corrosion resistance, etc.) necessary for containing the aqueous electrolyte solution and cells / batteries. For example, a cell and a plurality of additional cells, or a battery and a plurality of additional batteries, may be contacted simultaneously, such as by immersion in a common aqueous electrolyte solution. The total number of cells and / or batteries may be, for example depending on the size of the contacting vessel, at least about 10, at least about 50, or at least about 100, with higher numbers generally leading to greater economies of scale.EXAMPLES

[0034] The following examples are set forth as representative of the present invention. These examples are not to be construed as limiting the scope of the invention as other equivalent embodiments will be apparent in view of the present disclosure and appended claims.Example 1 — initial evaluation of cell discharge / corrosion characteristics

[0035] Immersion of cells in aqueous solutions of sodium chloride (NaCl), sodium carbonate (Na2COa) and sodium bicarbonate (NaHCCF), at concentrations of 1 wt-%, 5 wt-%, and 10 wt-%, demonstrated that these solutions were capable of discharging both cylindrical metal can 18650 cells and pouch format cells to a low voltage. The results of the measured open circuit voltage (OCV) over time are shown in FIG. 1, with the left-hand graph and right-hand graph illustrating the behavior of the can-type cells and pouch-type cells, respectively. In this regard, the cylindrical metal can 18650 cells were made with steel. When the plastic labels were removed from the cells and the cells were placed in concentrated salt solutions, corrosion occurred and iron was dissolved. This could be observed as froth. Accompanying this corrosion, dissolution of the positive terminal of the cell could occur, thereby exposing inner parts of the cell.

[0036] With respect to the pouch format cells, the outer casing was made of plasticized aluminum, with a thin layer of aluminum being sandwiched between two layers of plastic. Scratching or scraping the outer plastic layer was particularly effective for initiating corrosion of the aluminum. The tabs of the pouch format cells, which were either Ni-coated copper, pure Ni, or pure Al, appeared to be corroded faster than the aluminum of the casing. From past work, even pinholes in the plastic layer inside the cell (next to the electrodes) caused corrosion of the aluminum. Scoring of the pouch casing was seen to facilitate discharge of the cells.

[0037] From this initial evaluation, it was found that NaCl was particularly effective in corroding the cylindrical metal can. This facilitates removal of the can, following discharge of the cells, both of which removal and discharge are often necessary for further processing.Advantageously, the recycling process is expedited in this manner. A large container of salt solution would allow for discharge and corrosion of multiple, for example 100-1,000 or more, cells on a commercial scale operation, thereby providing cost advantages.Example 2 — Li-ion cell, metal can cell casing dissolution studies

[0038] A study was performed to investigate dissolution of the cell metal casing of cylindrical lithium-ion cells in various solvents. The intent was to determine the solution type (e.g., salt, acid, or base) and concentrations needed to cause dissolution of the metal casing in order to facilitate removal of electrodes and provide a benign electrode for recycling and regeneration. In view the prospect of scaling the method to commercial capacities with a large number of cells, the solutions were prepared using tap water. The solution mass was 1 kg in all experiments, with slight variations in volume due to density differences. For this study, 18650 model Li-ion cells by a leading commercial cell manufacturer were used. The label, namely a shrink-wrap plastic covering of the metal can of the cell, as well as the white donutshaped insulator material, were removed before placing the cells in the various solutions. Also before the testing, the state of charge of the cell was set to 50%, and corresponding voltage and capacity were 3.6 V and 3.5 Ah, respectively.

[0039] After placing the cells in the solution, the cells were periodically removed from the solution to record the cell open circuit voltage (OCV), and photographs were taken. According to the specific protocols, these actions were taken at 0, 2, 4, 6, 8, 24, 48, 72, 96, and 168 hours from the start of solution immersion. Cell mass, solution pH, and solution conductivity, were determined initially (0 hours) and at the end of the test.A. Results with NaCl Solutions of 1 wt-%, 5 wt-%, and 10 wt-%

[0040] With the 1 wt-% NaCl solution, this turned from clear to a brownish yellow color within 2 hours of cell immersion. A brown froth developed, which descended to the bottom of the beaker within a few days. A top part of the positive terminal dissolved in 4-6 hours, and a white deposit was observed on the positive terminal after this dissolution. With the 5 wt-% and 10 wt-% NaCl solutions, these turned from clear to a brownish yellow color within a few minutes of cell immersion. A brown froth developed, which descended to the bottom of the vessel (beaker) within a few hours. The positive terminal dissolved in 30 minutes, with part of this coming off of the cell.

[0041] In these tests, intense bubbling was observed during first few hours after immersion. Bubbling intensity was reduced after the positive terminal dissolved. The bubblingintensity / gas formation varied with the solution strength, according to 1 wt-% < 5 wt-% < 10 wt-%. After the positive terminal dissolved, the OCV was measured from the side of the positive terminal that was still left (metal ring on the edge). A large drop in cell voltage was caused by the NaCl solution entering the cell. After the solution entered, cell voltage became unstable. Certain measured parameters obtained for the tests with NaCl solutions are summarized in Table 1 below.Table 1

[0042] The voltage behavior over time of cylindrical metal can 18650 cells, immersed in NaCl solutions of 1 wt-%, 5 wt-%, and 10 wt-% concentration, is summarized in FIG. 2.

[0043] From destructive physical analysis performed following the test using 5 wt-% NaCl, it was determined that this solution had entered the cell over the course of the testing. The outer separator layer of the cell was discolored, and there was also discoloration and corrosion of the Cu current collector, with slight delamination of the graphite electrode. The Al current collector appeared less affected by the NaCl solution. Approximately 30% of the length of the jellyroll from the positive electrode was stuck together and could not be unrolled. The cell required some manual disassembly after the test period.B. Results with Na CCh Solutions of 1 wt-%, 5 wt-%, and 10 wt-%

[0044] With all of the Na2COa solutions, some cloudiness occurred due to formation of a white precipitate upon mixing with the tap water. With the 1 wt-% Na2COa solution, a thick surface deposit formed on the positive terminal after about 8 hours, and this could not be removed even by scraping, making recordation of the cell voltage difficult. Yellowish discoloration of the solution, with precipitation, was observed similar to what was observed with the 1 wt-% NaCl solution. With the 5 wt-% and 10 wt-% Na2COa solutions, a blackdeposit was formed on the positive electrode, but cell voltage could still be ascertained. Also, no yellowish discoloration of the solution was observed.

[0045] In these tests, bubbling due to gas formation was less intense relative to that observed for the NaCl solutions. The bubbling intensity / gas formation varied with the solution strength, according to 1 wt-% < 5 wt-% - 10 wt-%. Observations with the 5 wt-% and 10 wt-% solutions were similar. One week after removing the cells from the solutions, OCV rebounded to 2.3-2.4 V. Certain measured parameters obtained for the tests with Na COa solutions are summarized in Table 2 below.Table 2

[0046] The voltage behavior over time of cylindrical metal can 18650 cells, immersed in NaaCOa solutions of 1 wt-%, 5 wt-%, and 10 wt-% concentration, is summarized in FIG. 3.C. Results with HC1 Solutions of 1 wt-% and 5 wt-%

[0047] With the 1 wt-% HC1 solution, small pieces (-1 mm) of the positive terminal detached at 27 minutes after immersion, and the central protruded part of the positive terminal fell out in 30 minutes. The positive terminal dissolved layer by layer and was completely dissolved after 4 days in solution. No froth or yellow color was seen (as was seen in NaCl solution). Corrosion and the formation of a crack on the cell can were observed. Approximately 50% of the length of the can was corroded. With the 5 wt-% HC1 solution, gas formation was very intense during the first hour following immersion. Bubbling due to the gas formation was observed during the entire test. Also, the central protruded part of the positive terminal became loose in 15 minutes, and the positive terminal was completely dissolved in 2 hours. Severe corrosion of the cell can was observed after 72 hours. The 5 wt-% HC1 solutionappeared to dissolve the steel under the nickel plating on the can, and this solution had a greenish hue after 1 week.

[0048] In these tests, bubbling due to gas formation was more intense compared to all other solutions tested. The bubbling intensity / gas formation varied with the solution strength, according to 1 wt-% < 5 wt-%. Cell voltage measurement became unreliable after solution entered the cell. Certain measured parameters obtained for the tests with HC1 solutions are summarized in Table 3 below (with test results for 3 wt-% HC1 solution pending).Table 3

[0049] The voltage behavior over time of cylindrical metal can 18650 cells, immersed in HC1 solutions of 1 wt-% and 5 wt-% concentration, is summarized in FIG. 4.

[0050] From destructive physical analysis performed following the test using 1 wt-% HC1, it was determined that the steel can was dissolved approximately 25% of the length from the positive terminal, with only what is assumed to be the Ni plating on the can left in those areas. The cell header area had become completely loose during the immersion in this acid. Disassembling the cell by hand was rendered easier, compared to a pristine cell. Whereas the jellyroll could not be pulled out of the can, this can could nonetheless be peeled off easily using pliers. Possibly further aiding removal of the jellyroll would be performing this step on a wet cell rather than a dry one. Corrosion of both the Al and Cu current collectors was observed over approximately 25% of the length from the positive terminal.D. Results with NaOH Solutions of 1 wt-% and 5 wt-%

[0051] With both the 1 wt-% and 5 wt-% NaOH solutions, slight corrosion and discoloration of the positive terminal of the cell were observed. The bubbling intensity / gas formation varied withthe solution strength, according to 1 wt% < 5 wt%. Cell voltage measurement gave somewhat inconsistent readings, particularly in the 5 wt-% NaOH test. No rebound in the OCV was observed after removing cell from solution, and the fluctuating cell voltage during the test could indicate that the solution was able to enter the cell trough the crimp seal. Certain measured parameters obtained for the tests with NaOH solutions are summarized in Table 4 below (with test results for 10 wt-% NaOH solution pending).Table 4_

[0052] The voltage behavior over time of cylindrical metal can 18650 cells, immersed in NaOH solutions of 1 wt-% and 5 wt-% concentration, is summarized in FIG. 5.E. Determination of metals in the solutions following testing

[0053] Following the cell corrosion / dis solution testing, 2 ml of each solution (NaCl, Na COa, HC1, and NaOH) at 5 wt-% initial strength (z.e., prior to the testing / immersion) was diluted with 8 ml HPLC water, giving sample volumes of 10 ml. Two to three wavelengths were used to measure the concentrations of each of the elements Li, Co, Ni, Mn, Al, Cu, and Fe. Some wavelengths were more sensitive than others, and average concentrations were calculated from all the wavelengths used for each element. The results of the metal concentrations as determined by inductively coupled plasma mass spectroscopy (ICP-OES), are summarized in Table 5 below.Table 5

[0054] With respect to the metals analyses, whereas no iron was detected in the 5 wt-% NaCl solution, a brownish / yellowish sediment that formed during the test was found to contain iron and aluminum. Also, whereas no visual signs of can corrosion were observed in the 5 wt-% NaOH solution, the lithium and aluminum detected in this solution through ICP-OES suggest that it could enter the cell and cause corrosion of the aluminum current collector. This is supported by the dramatic drop of cell voltage during solution immersion. The 5 wt-% HC1 solution contained large amounts of iron, which originated from the severely corroded metal can. The estimated total mass of iron in this solution was approximately 2 grams). Moreover, high concentrations of lithium, cobalt, nickel, manganese, aluminum, and copper were also observed. This shows that the solution had dissolved the metals in the cathode material and current collectors, as well.

[0055] Overall, aspects of the invention relate to method for recycling cells and batteries, utilizing contact with an aqueous electrolyte solution to cause at least some corrosion / dissolution, thereby facilitating safe recycling and possibly further allowing for recovery of valuable metals from the products of corrosion. Those skilled in the art, having knowledge of the present disclosure, will recognize that various changes can be made to these methods in attaining various advantages described herein and possibly other advantages, without departing from the scope of the present disclosure. As such, it should be understood that the features of the disclosure are susceptible to modifications and / or substitutions, and the specific embodiments described herein are for illustrative purposes only, and not limiting of the invention as set forth in the appended claims.

Claims

CLAIMS:

1. A method for recycling a cell, the method comprising contacting the cell with an aqueous electrolyte solution, wherein the cell comprises a housing having an electrode assembly disposed therein, said housing comprising a metallic layer, and wherein the contacting is performed under dissolution conditions effective to dissolve at least a portion of the metallic layer.

2. The method of claim 1, wherein the dissolution conditions are effective to dissolve at least about 50% by weight of the metallic layer.

3. The method of claim 1 or claim 2, wherein the housing is in the form of a cylindrical can or a prismatic can.

4. The method of claim 3, wherein, prior to said contacting, an outer plastic layer of the cylindrical can or the prismatic can is partially or completely removed to increase exposure of the metallic layer to the aqueous electrolyte solution.

5. The method of claim 1 or claim 2, wherein the housing is in the form of a pouch.

6. The method of claim 5, wherein, prior to said contacting, an outer plastic layer of the pouch is penetrated to increase exposure of the metallic layer to the aqueous electrolyte solution.

7. The method of any one of claims 1 to 6, wherein the contacting is performed by immersing the cell in the aqueous electrolyte solution.

8. The method of any one of claims 1 to 7, wherein the aqueous electrolyte solution is a solution of a salt, an acid, or a base.

9. The method of claim 8, wherein the salt is a chloride salt, a carbonate salt, or a bicarbonate salt.

10. The method of claim 9, wherein the salt is selected from the group consisting of NaCl, Na2CO3, and NaHCO311. The method of any one of claims 8 to 10, wherein the salt, acid, or base is present in the aqueous electrolyte solution in an amount from about 1 wt-% to about 10 wt-%.

12. The method of claim 8, wherein the acid is selected from the group consisting of HC1, H2SO4, and HNO3.

13. The method of claim 8 or claim 12, wherein the aqueous electrolyte solution has a pH of less than about 6.

14. The method of claim 8 or claim 11, wherein the base is NaOH or KOH.

15. The method of any one of claims 1 to 14, wherein the dissolution conditions include a contacting time of at least about 12 hours, beyond discharging the cell to a voltage of 1 volt or less.

16. The method of any one of claims 1 to 15, wherein the dissolution conditions include a contacting time of at least about 48 hours.

17. The method of any one of claims 1 to 16, wherein the dissolution conditions are effective for removal of the electrode assembly, without cutting said housing.

18. The method of any one of claims 1 to 17, wherein the dissolution conditions are effective to dissolve at least about 50% by weight of a positive terminal of the cell, or to separate the positive terminal of the cell.

19. The method of any one of claims 1 to 18, further comprising, following said contacting, recovering metals dissolved in said aqueous electrolyte solution.

20. The method of any one of claims 1 to 19, wherein the method comprises contacting the cell and a plurality of additional cells with the aqueous electrolyte solution.

21. The method of claim 20, wherein the contacting is performed by immersing the cell and plurality of additional cells in the aqueous electrolyte solution.

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