WO2018169830A1

WO2018169830A1 - A method of producing pre-lithiated graphite from recycled li-ion batteries

Info

Publication number: WO2018169830A1
Application number: PCT/US2018/021927
Authority: WO
Inventors: Andrew Minor; Gao Liu; Abraham Anapolsky; Julian SABISCH
Original assignee: The Regents Of The Universtiy Of California
Priority date: 2017-03-13
Filing date: 2018-03-12
Publication date: 2018-09-20

Abstract

The disclosure provides for methods to recover and recycle anode and/or cathode materials from batteries so that these recovered anode and/or cathode materials can then be used in the construction of new batteries.

Description

A METHOD OF PRODUCING PRE-LITHIATED GRAPHITE FROM RECYCLED LI-ION BATTERIES

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. §119 from Provisional Application Serial No. 62/470,782, filed March 13, 2017, the disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

[0002] The disclosure provides methods for recycling anode and/or cathode materials from batteries. These recovered anode and/or cathode materials can then be used to make anodes for new batteries .

BACKGROUND

[0003] Conventional Li-ion battery recycling uses a batch chemical process to homogenize and extract only a few metals, e.g. Co, Cu, and Al . The processes are destructive and do not allow for preservation of the material properties of the other Li-ion battery components .

SUMMARY

[0004] This disclosure provides methods to extract the

components of a lithium ion battery for complete recycling, and in the case of the anode, re-manufacturing of graphite. This is accomplished by opening cells at a specific state of degradation

(when a cell is "resistively failed") under specific conditions. The graphite anode is cleaned, using a chemical process. The graphite is then ready for re-use in new graphite or Si ( Sn) -graphite anodes. The innovative methods disclosed herein allow for a specific level of pre-lithiation to be reached, by blending and testing the graphite to achieve a suitable anode material for specific Li ion battery applications, e.g. high power, high energy, novel anodes, etc. The innovative methods disclosed herein can therefore provide for the re-manufacturing of recovered graphite (and thus re-used) for use as an anode, as well as, as provide for a source of pre- lithiation .

[0005] Accordingly, the disclosure provides for methods to reuse anode materials from used commercial lithium ion batteries in order to make new batteries. In a particular embodiment, the disclosure provides for methods that can extract graphite from lithium ion batteries using mechanical separation which can then be cycled stably using current. As presented herein, the recovered graphite was found not to substantially degrade after the capacity loss of the original lithium ion cell. In addition, the recovered graphite showed some degree of pre-lithiation, leading to the possibility that recycled graphite could act as a lithium source in future battery recycling development work.

[ 0006] In a particular embodiment, the disclosure provides a method to recover anode and/or cathode materials from one or more cells of a used battery, comprising: cooling the one or more cells to a temperature determined by measuring the aggregate resistivity of a plurality of cells; opening the one or more cells under a dry atmosphere; separating the anode and cathode material from the other battery cell components; and cleaning separately the anode and cathode materials using one or more solvents to remove any

contaminants, wherein the cleaned anode materials can then be reused in batteries. In another embodiment, the cleaning step further comprises cleaning the anode and cathode materials using supercritical CO₂. In yet another embodiment, the dry atmosphere has a dew point below -50 °C. In a further embodiment, the dry atmosphere comprises an atmosphere of nitrogen or argon that is devoid of oxygen and water vapor. In a further embodiment, the one or more cells are cooled under a dry atmosphere. In yet a further

embodiment, the one or more solvents are dimethyl carbonate (DC) , N- methyl-2-pyrrolidone (NMP) , or a mixture thereof. In a particular embodiment, the anode materials comprise graphite. In a further embodiment, the graphite is pre-lithiated . In another embodiment, the one or more cells are from used batteries that are in a resistively failed degradation state. In yet another embodiment, the used batteries are lithium ion batteries. In a further embodiment, the used batteries are lithium ion batteries from laptops or electric vehicles. In yet a further embodiment, the disclosure provides for an anode material made by the methods disclosed herein.

[ 0007 ] In a certain embodiment, the disclosure also provides a method for making an anode sheet from anode materials recovered from recycled batteries, comprising: making a homogenized slurry comprising a binder agent and the recovered anode material disclosed herein; spreading, spraying, or depositing the slurry over the surface of a thin sheet of conductive material; and drying the slurry to form an anode sheet. In another embodiment, the binder agent is polyvinylidene fluoride (PVDF) . In yet another embodiment, the slurry further comprises NMP . In a further embodiment, for every gram of anode material, 1 to 5 milliliters of NMP is added to the slurry. In yet a further embodiment, the conductive material is a thin sheet of copper. In another embodiment, the slurry is dried for at least 12 hours at ambient temperature. In another embodiment, a tape caster is used in order to create an anode of uniform thickness. In yet another embodiment, the anode sheet has a thickness between 50 ]im to 150 μπι. In a further embodiment, the method to make the anode sheet is performed under a dry atmosphere (e.g., a dew point below -50 °C) . In a further embodiment, the dry atmosphere is an atmosphere of nitrogen or argon that is devoid of oxygen and water vapor. In yet a further embodiment, the disclosure provides for an anode sheet produced by a method disclosed herein.

[ 0008 ] In a particular embodiment, the disclosure further provides a method of forming battery anodes from an anode sheet, comprising: cutting or punching out a portion of the anode sheet disclosed herein to generate anodes for use in batteries. In another embodiment, the anode sheet has been calendered using a roller (s) prior to cutting or punching. In a further embodiment, the battery the method further comprises heating in vacuo the anodes at an elevated temperature for greater than 12 hours. In a certain embodiment, the anodes are configured to be used in lithium ion batteries. In a further embodiment, the disclosure provides for one or more battery anodes produced by a method disclosed herein. In yet a further embodiment, the disclosure provides for a battery comprising one or more battery anodes disclosed herein.

[ 0009] In a particular embodiment, one or more steps of a method disclosed herein are performed using an automated process.

[ 0010 ] The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims .

DESCRIPTION OF DRAWINGS

[0011] Figure 1A-D provides images and diagrams of the internal components making up the lithium ion cells from a laptop battery. (A) image showing the inside of a laptop battery, (B) a close-up image of an 18650 commercial lithium ion cell and a schematic of its internal design, (C) a picture of an 18650 lithium ion cell that has been opened, and (D) shows a flow chart depicting a general process of the disclosure.

[0012] Figure 2A-B presents the profiles of the initial cycle for both (A) virgin and (B) recycled graphite.

[0013] Figure 3A-B presents the capacitance for both (A) virgin and (B) recycled graphite done until stable cycling.

[0014] Figure 4 presents the voltage and capacitance profiles for the lithiated and the de-lithiated anode kept completely under a dry atmosphere.

[0015] Figure 5 presents the results of voltage and current experiments with virgin graphite anodes.

[0016] Figure 6 presents the results of capacitance experiments with virgin graphite anodes.

[0017] Figure 7 presents the results of voltage and current experiments with recycled graphite anodes containing 3% PVDF and 0.5% CMC .

[0018] Figure 8 presents the results of capacitance experiments with recycled graphite anodes containing 3% PVDF and 0.5% CMC.

[0019] Figure 9 presents the results of voltage and current experiments with recycled graphite anodes containing no additives.

[0020] Figure 10 presents the results of capacitance experiments with recycled graphite anodes containing no additives.

[0021] Figure 11 presents the results of voltage and current experiments with recycled graphite anodes of greater thickness.

[0022] Figure 12 presents the results of capacitance experiments with recycled graphite anodes of greater thickness.

DETAILED DESCRIPTION

[0023] As used herein and in the appended claims, the singular forms "a, " "an, " and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "an anode" includes a plurality of such anodes and reference to "lithium ion cell" includes reference to one or more lithium ion cells and equivalents thereof known to those skilled in the art, and so forth.

[ 0024 ] Also, the use of "or" means "and/or" unless stated otherwise. Similarly, "comprise," "comprises," "comprising"

"include," "includes," and "including" are interchangeable and not intended to be limiting.

[ 0025] It is to be further understood that where descriptions of various embodiments use the term "comprising," those skilled in the art would understand that in some specific instances, an embodiment can be alternatively described using language "consisting

essentially of" or "consisting of."

[ 0026] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art. Although many methods and reagents similar or equivalent to those described herein, the exemplary methods and materials are presented herein.

[ 0027 ] After their introduction in the early 1990' s lithium ion batteries have quickly become the leading choice in portable energy storage for all electronic devices. In the future, it is expected that the importance of Lithium ion batteries will increase greatly due to demands from emerging electric vehicle technologies and existing portable electronic devices. As of 2008, more than 3 billion Li-ion batteries cells have been sold. With an average weight of 0.045 kg/battery of total battery, this accounts for 135 million metric tons of mass. Conservative predictions of electric vehicle growth, estimate that at least 1 million electric vehicles not including hybrid electric and plug-in hybrid electric vehicles will be produced in 2016. As Lithium ion battery packs currently provide the most compelling battery technology for electric vehicles at present and approximately 28 kWh per vehicle will be required, an additional 28 GWh. With an average capacity of 0.25 kW/kg the global lithium demand would increase by 112 million kg. With less

conservative estimates, the demand would more than double within a seven-year time span. [ 0028 ] Waste management is currently seen as only a minor problem when looking at the lithium ion battery industry. But with the expected future increase of battery production, new methods for cell disposal and recycling must be developed. Present recycling procedures aim only to recover the heavy elements of cobalt and copper from the Lithium ion battery. The average recycling yield is 3% of material recovered by weight, usually cobalt and copper, resulting in over 130 million tons of waste material. While some of the waste is incinerated, much recoverable material is discarded into landfills. Prevailing methods for recycling Li-ion batteries commonly include incineration of the waste material to recover the heavier copper and cobalt; another main method is mastication of the batteries then chemical leaching to recover the cobalt and copper. Both methods are destructive and do not allow for preservation of the material properties through the recycling.

[ 0029] Previous research has shown that the mechanisms of battery failure are generally electrolytic and anode based

processes. Oxidation of the electrolytic solution along with lithium plating on the cathode or dendrite formation, are principle causes for capacity loss. The integrity of the graphitic anode material is generally unaffected by the loss of cell capacity. Repeated cycling can affect the electrical contact between the graphitic active material and the copper substrate by cracking and slowly

mechanically separating the active material, increasing the intrinsic resistivity of the anode and reducing total capacitance by electrically isolating active material. At the end of the battery life the anode will be chemically very similar to the beginning of battery life, but will have much worse mechanical and electrical properties .

[ 0030 ] Currently, high-power, or novel high-energy density, anodes suffer from high-first cycle loss of elemental Li, the Li has to be supplied by the cathode, or in the form of a pre-lithiation step, using e.g. stabilized lithium metal powder (SLMP) such as LiCC>3. Pre-lithiation adds cost, both in raw materials and in-line manufacturing costs. High first cycle loss can de-rate the energy density of a Li-ion battery by as much as 20% in high power graphite cells and 20-50% in Si, Sn, or Si-Sn-graphite anodes. Further, graphite has to be mined, or synthesized from fossil fuel sources, making it a non-commodity resource.

[ 0031 ] Current commercially produced anodes are cast onto copper substrates with polymer binders and other additives mixed into the graphite base in order to improve mechanical cohesion and electrical conduction. The polymer binders are exceedingly important because graphite has a very low affinity for copper making it difficult to create even substrates that will stick well to the substrate. This property allows for anode material to be easily recoverable from the copper substrates through mechanical means.

[ 0032 ] In general, the disclosure provides methods which can solve the aforementioned problems; using the methods disclosed herein a high percentage of graphite can be re-supplied back into the manufacturing stream, while simultaneously providing pre- lithiated anode materials. The method steps and resources outlined in this disclosure provide for anode materials that are far less intensive than mining or synthesizing graphite.

[ 0033] The disclosure provides methods that allow for the recovery of anode materials having minimal capacity from a depleted battery via mechanical separation. The disclosure further provides that the recovered anode materials can then be re-casted as a new anode for a battery cell. There are several potential benefits from recycling the anode material, such as providing a source of anode material that has already been preprocessed with additives. This diminishes the need for finding new sources and greatly reduces the waste stream while simultaneously providing a source for high quality graphite that has already been pre-cycled. Additionally, anode materials, such as graphite, form a passivation layer, the solid electrolyte interface (SEI), during its initial cycle that aids in the conduction of lithium ions. The SEI incorporates some of the lithium anodes present in the cell into itself, causing these ions to become electrically inactive and results in some first cycle capacity loss. By recycling the graphite from lithium ion batteries, the first cycle loss should be reduced by having graphite that already contains an SEI layer. The experiments presented herein show that the graphite can be pre-lithiated when assembled into a cell allowing for the anode itself to act as a lithium source. If the extent of the lithiation is large enough, the first cycle of the battery could show a larger output capacitance than input, due to the lithium already being present in the graphite.

[ 0034 ] The experiments described herein demonstrate that graphite can be successfully recovered from used battery cells and reprocessed to form stable anodes. It has been further shown herein that graphite can easily be extracted from used commercial lithium ion cells using the methods of the disclosure, and that the graphite taken from these cells did not degrade due to heavy cycling. Pre- lithiation of the recycled graphite was observed, and while it is not extensive, the lack of greater pre-lithiation is due to the need to discharge the batteries because of safety concerns when opening the commercial cells. The reprocessed anodes cycled as well as the virgin graphite, showing stable capacity and minimal loss past the initial first cycle loss.

[ 0035] The methods of the disclosure also provide for the preservation of any SEI that has been formed during the initial life cycle of the graphite and potentially the recycled graphite can provide a significant source for lithium. Due to the safety constraints, the dissembling of charged cells requires great care, which can be facilitated by disassembling the cells at very cold temperatures, such as the temperature of liquid nitrogen (-210 °C) or lower. Use of cold temperatures increases the resistance of the cells to almost infinity, suppressing short circuiting of the battery when opened.

[ 0036] Conventional Li-ion battery recycling uses a batch chemical process to homogenize and extract only a few metals, e.g., Co, Cu, and Al . The methods described herein provide a new approach to extract the components of a Li ion battery for complete

recycling, and in the case of the anode, re-manufacturing of graphite. This is accomplished by opening cells at a certainty of degradation, e.g., when the cell has "resistively failed" under specific conditions. The graphite anode is cleaned, using a washing process described herein. The graphite is then ready for re-use in new graphite or Si (Sn) -graphite anodes. The innovative processes disclosed herein allow for a specific level of pre-lithiation to be achieved by blending and testing the graphite to achieve a suitable anode material for specific battery applications, e.g. high power, high energy, novel anodes, etc. A unique feature of the methods of the disclosure is that recovered graphite can be re-manufactured (and thus re-used) as an anode, as well as provide a source of pre- lithiation .

[ 0037 ] New or used batteries may be used by the methods disclosed herein as sources of anode materials. In a particular embodiment, the new or used batteries are lithium ion batteries. In a further embodiment, the source of anode materials is from batteries for laptops, vehicles and/or other electronic devices, including but not limited to battery packs for various tools, instruments, toys, and machines. In yet a further embodiment, the source of anode materials is 18650 lithium ion cells from laptop battery packs, vehicle battery packs etc., 20700 or 21700 lithium ion cells. For the methods disclosed herein, the batteries should have pre-lithiation of the graphite. Therefore, the batteries should not be fully discharged. To allow for maximum safety, the cell voltages should be in the range of 2-3.5 volts in low capacity cells prior to opening the batteries. Alternatively, cells having greater voltages and capacity may be used, but the cells should be chilled to the temperature of liquid nitrogen or lower prior to opening. Generally, the cells are cooled to a temperature that is determined by measuring the aggregate of a plurality of cells to be opened. Furthermore, the cells are also standardly cooled under a flowing dry atmosphere (e.g., an atmosphere of very dry air, nitrogen, argon, etc.)

[ 0038 ] Typically, the cells should be opened under a very dry atmosphere (e.g., a dew point below -50°) . Examples of dry atmospheres include atmospheres containing noble gases (e.g., argon), nitrogen, or very dry air.

[ 0039] While any manner or method may be used to open cells, care should be taken so as to minimize contamination of the anode material with cathode material. Typically, the method for opening the battery cell uses a physical cutting device, such a saw, cutter or knife. Alternatively, cutting devices that use energy may also be used, such as lasers. It is further contemplated that the battery cells may be opened using automated cutting devices in order to increase efficiency and to be able to process a far larger number of battery cells per time.

[ 0040 ] After the battery cell has been opened, the anode material can be mechanically separated from the rest of the components. As with opening the cells, any number of methods may be used to obtain the anode material from the opened cells (e.g., scraping or shaking off the cathode material from a copper

substrate) . Moreover, as before, care should be taken so as to minimize contamination of the anode material with cathode material. It is further contemplated that mechanical separation of the anode from the other battery components can be accomplished by using an automated device/system.

[ 0041 ] After recovering the anode material, the anode material may be further processed by washing with one or more solvents. In particular embodiment, one or more solvents include a carbonate- based solvent, such as dimethyl carbonate (DMC) , a polymer solvent, such as iV-methyl-2-pyrrolidone (NMP) , and mixtures thereof. The anode material can then be reused to make new battery anodes. In a particular embodiment, polyvinylidene fluoride (PVDF) is added to the recovered anode material. The amount of PVDF added should be so as to have a percentage/weight, such as 1% to 10% PVDF by weight. In a further embodiment, PVDF is added until 2% to 5% by weight is reached. A slurry can then be made by mixing a composition comprising the recovered anode material (with or without PVDF) and one or more solvents. In a particular embodiment, the one or more solvents are typically a high boiling point polar aprotic low viscosity solvent (e.g., a polymer solvent, such as N-methyl-2- pyrrolidone (NMP) ) . While any method may be used to mix the slurry

(e.g., using stirrers, mixers, shakers, rockers, tumblers, etc.) better results are obtained if the slurry is mixed so that it is homogenous. The viscosity of the slurry may be controlled so as to generate an anode sheet of a certain thickness. While any number of methods may be used to increase or decrease the viscosity of the slurry, an easy and controllable method is to regulate the amount of solvent added to the anode material. For example, using more solvent will lower the viscosity of the resulting slurry. In a particular embodiment, the method uses between 1 mL and 20 mL of solvent (e.g., NMP) per gram of anode material. In a further embodiment, between 2 mL and 10 mL, or between 3 mL and 5 mL of solvent per gram of anode material is used. One method of cleaning is to utilize supercritical CO₂ in combination with the

aforementioned solvents.

[ 0042 ] An anode sheet can then be formed by spreading,

depositing, sputtering, or pouring the slurry over the surface of a conductive material (e.g., gold, silver, copper etc. film) . In a particular embodiment, the conductive material is a sheet having a thickness between 5 ]im to 50 μπι, 7.5 μπ\ to 25 μπι, or 10 μπ\ to 25 μπι. In one embodiment, the sheet is a copper sheet. In another or further embodiment, the anode sheet has a certain thickness, such as at least 25 μπι, at least 50 μπι, at least 75 μπι, at least 100 μπι, at least 150 μπι, at least 200 μπι, or at least 300 μπι. Methods to control the thickness of the anode sheet include the use of molds or tape casting. The anode sheet is then dried at ambient temperature or at an elevated temperature for at least 5 hours, at least 10 hours, at least 12 or at least 16 hours. The anode sheet may be further processed so as to reduce porosity and/or increase anode density by using presses or calendaring with rollers. In particular embodiment, the anode sheet is generated by using an automated device /system.

[ 0043] Anodes for use in batteries (e.g., lithium ion batteries) can then be cut or punched out of a portion of the anode sheet.

Alternatively, if large anodes are desired multiple anode sheets may be combined together. In particular embodiment, the anodes cut from the anode sheet are configured so as to be used in lithium ion cells (e.g., 18650 (4/3AF) , 18500, 14500 (AA) , 14430 (4/5AA) 10440 (AAA) , 14650 (7/5AA) , 17500(A) , 20700, 21700, 26650 (Long C) , 26650M, 38120P(M) , 40160S(Long M) , RCR123A, CR123A-Dummy, 1-2C rate, High Power, 2032 button cell, or 2450 button cell) . Any method may be used to cut the anodes from the anode sheet including the use of lasers, cutting devices, punches, dies, and the like. In particular embodiment, the anodes are cut from the anode sheet using an automated

device/system. The anodes may then be used as is or may be further processed to remove any remaining water, solvent and/or oxygen by heating in vacuo at an elevated temperature for at least 2 hours, at least 5 hours, at least 10 hours, at least 12 or at least 16 hours.

[ 0044 ] FIG . ID shows a general flow diagram of a method of the disclosure. At 10 one or more lithium batteries are obtained. The batteries can be degraded, recycled, new, etc. Typically, the batter is at a certainty of degradation, e.g., when the cell has "resistively failed" under specific conditions. Such batteries can be for laptops, vehicles and/or other electronic devices, including but not limited to battery packs for various tools, instruments, toys, and machines. Exemplary batter types include lithium ion cells (e.g., 18650 ( 4 /3AF) , 18500, 14500 (AA) , 14430 (4/5AA) 10440 (AAA) , 14650 (7/5AA), 17500(A), 20700, 21700, 26650 (Long C) , 26650M, 38120P(M), 40160S(Long M) , RCR123A, CR123A-Dummy, 1-2C rate, High Power, 2032 button cell, or 2450 button cell) .

[ 0045 ] The battery is tested to determine its charge and resistivity. The battery ideally should not be fully discharged as a fully discharged battery may lack any useful recyclable elements. If the charge is greater than about 3.5 volts the battery should be further discharged ( 20 ) to between about 0.5-3.5 volts (e.g., 2.0- 3.5 volts) . This level of charge provides a safer level for processing. The battery can then be, or may be alternatively, cooled to increase the resistivity in an inert atmosphere ( 30 ) . The atmosphere is typically a flowing dry nitrogen or argon atmosphere devoid of oxygen and water. The battery may be cooled using various cooling agents such as liquid nitrogen and the like.

[ 0046 ] The battery is the deconstructed to separate the cathode, anode (e.g., graphite/copper material) and other battery elements

( 40 ) . Typically, the cells should be opened under a very dry atmosphere (e.g., a dew point below -50°) . Examples of dry atmospheres include atmospheres containing noble gases (e.g., argon), nitrogen, or very dry air. Typically, the method for opening the battery cell uses a physical cutting device, such a saw, cutter or knife. Alternatively, cutting devices that use energy may also be used, such as lasers. It is further contemplated that the battery cells may be opened using automated cutting devices in order to increase efficiency and to be able to process a far larger number of battery cells per time. Care is taken to avoid contaminating the anode material with cathode material. After the battery cell has been opened, the anode material can be mechanically separated from the rest of the components. Separate the anode material typically comprising copper substrates with polymer binders and other additives mixed into the graphite base.

[0047] Once the anode material is isolated from the other components, the anode material (e.g., graphite/copper) is

rinsed/washed/soaked in a high boiling point polar aprotic low viscosity solvent (50) . The solvent may be a single solvent or co- solvent mixture. The solvent/co-solvent is a carbonate solution. An exemplary carbonate solution is dimethyl carbonate and N-methyl-2- pyrrolidone. This solution is used to remove excess lithium salts and polymer binder (s) that are present in the anode material. The graphite material is then separated from the conductive laminate (e.g., copper) (60). Typically a supercritical cleaning solvent is used such as, for example, CO₂, ethane, propane, ethylene,

propylene, methanol, ethanol, acetone and nitrous oxide. Typically CO₂ is used. Steps 50 and 60 may be reversed in their order. The resulting graphite preparation may be stored in a high boiling point polar aprotic solvent such as, e.g., N-methyl-2-pyrrolidone until used for casting. Either before or after storing the graphite the graphite material may be sorted, sized, milled etc. as desired (70) . The resulting graphite material can be used in the formation of new electrode materials. For example, the graphite material may be mixed into a slurry (80) and then used to form films of graphite material for battery preparation (90) . In a particular embodiment, polyvinylidene fluoride (PVDF) is added to the recovered anode material. The amount of PVDF added should be so as to have a percentage/weight, such as 1% to 10% PVDF by weight. In a further embodiment, PVDF is added until 2% to 5% by weight is reached. A slurry can then be made by mixing a composition comprising the recovered anode material (with or without PVDF) and one or more solvents. Any method may be used to mix the slurry (e.g., using stirrers, mixers, shakers, rockers, tumblers, etc.) better results are obtained if the slurry is mixed so that it is homogenous.

[0048] An anode sheet can then be formed by spreading,

depositing, sputtering, or pouring the slurry over the surface of a conductive material (e.g., gold, silver, copper etc. film) .

Typically copper is used. Anodes for use in batteries (e.g., lithium ion batteries) can then be cut or punched out of a portion of the anode sheet prepared from the recycled graphite.

Alternatively, if large anodes are desired multiple anode sheets may be combined together. In particular embodiment, the anodes cut from the anode sheet are configured so as to be used in lithium ion cells .

[ 0049 ] The following examples are intended to illustrate but not limit the disclosure. While they are typical of those that might be used, other procedures known to those skilled in the art may alternatively be used.

EXAMPLES

[ 0050 ] The source of anode active material must be considered.

Acquiring old depleted battery packs is the easiest method for finding graphite material, due to easy access to used battery packs from portable computers. The standard cells configuration for laptop battery packs is three 18650 type cylindrical Li-ion battery cells welded in series, put in parallel with other sets of three 18650 cells in series (e.g., see FIG . 1 ) . This forms a 10.8 volt battery with approximately 2.5 Ah per cell, depending on the quality of the batteries. The exact extent of lithiation, anode compositions, and anode degradation are unknown in these used battery cells. However, this situation most closely models real world recycling scenarios. Alternatively, it was possible to make control cells by cycling fresh commercial batteries at a rate of — C until the capacity

3

degrades sufficiently. For batteries having a 2.4 Ah capacity, the cycling was done at 0.83 A current for three hour charges and discharges at voltages of 4.2 V and 2.8 V for approximately 500 cycles .

[ 0051 ] It was important for the batteries to not be fully discharged; otherwise there would be no pre-lithiation of the graphite. Cell voltages of 2-3.5 volts in low capacity cells allowed for the maximum safety while still allowing for the graphite to be coated with lithium. The laptop cell packs are generally safer due to much heavier capacity loss as well as current discharge from leakage during a long inactive period. The cells were then placed under a dry atmosphere in order to open the cells for anode extraction. Argon is the standard gas used in lithium battery research due to its low leak rate and reactivity, but nitrogen gas can also be used to create a dry atmosphere, since nitrogen has very minimal reactivity with lithium.

[ 0052 ] A glovebox was used to open the cycled cells. Great care must be taken to ensure that the atmosphere in which the cells are opened is devoid of all water and to a lesser extent oxygen. Oxygen by coming into contact with the internal components of the cell can react with the lithium in the graphite to destroy the SEI layer, and water can react with the lithium phosphorus hexafluoride (LiPFe) to produce hydrogen fluoride (HF) . In order to ensure that no water is present, a desiccant was placed inside the glovebox prior to opening the cells. The atmosphere inside the glovebox was kept at a slightly higher pressure than atmospheric pressure to ensure that any leaks allowed gas to escape and to prevent external atmosphere from contaminating the controlled inner atmosphere. A flux of nitrogen gas was pumped through the box to keep the atmosphere stable. In addition, the antechamber transfer protocol for moving items into and out of the glovebox allows for the antechamber to reach maximum vacuum that can be re-filled with new nitrogen gas at least three times before moving the item into the interior of the glovebox, thus lowering the amount of contamination from the exterior of the glovebox. A constant flux of nitrogen was flushed through the box to ensure that atmosphere is continually refreshing itself.

[ 0053] Once the cells were inside the glovebox they were cut open with a tubing cutter and a rotary saw. The tubing cutter was used to take of the top and bottom of the cells as close to the contacts as possible. The tubing cutter allowed for a very

controlled cut and it reduced the amount of anode that was

contaminated with cathode material by cutting through multiple layers of the battery cell. After the ends were taken off, the rotary saw was used to carefully cut down the length of the cylinder. Ideally only a few electrode layers are cut with the rotary tool so as to limit anode contamination and cell shorting. Pliers can then be used to pry the metal casing open, thereby exposing the anode, polymer separator, and cathode that make up the battery cell. The electrode sandwich was then carefully unrolled and the anode was mechanically separated. This can be done in a number of ways. It is easiest to crumple the copper substrate and flake off the graphite; however, a spatula can also be used to scrape off the active material. The difference between anode and cathode is easily visible because graphite anodes are always deposited onto a copper substrate while the LiCoC>2 cathode is deposited onto aluminum. Great care must be taken in making sure that no cathode material gets mixed into the recovered graphite anode. It should also be noted that graphite color can be used to monitor the lithiation, and can change color from grey to purple, and from blue to gold depending on the extent of lithiation that the graphite is undergoing.

[ 0054 ] After recovering the graphite, it was washed in dimethyl carbonate (DMC) , a solvent for the LiPFe salt that is used in the electrolyte. The graphite was washed 3-4 times in DMC and filter paper was used to get rid of the excess while saving the graphite. After washing in DMC the graphite was washed with iV-methyl-2- pyrrolidone (NMP) , a polymer solvent to get rid of the

polyvinylidene fluoride (PVDF) binder that was used to help the graphite adhere to the copper substrate. After the PVDF was washed out, the graphite was presumed to contain only graphite and a conductivity enabling agent, such as acetylene black (AB) .

Additional samples were prepared with without washing with DMC and NMP, washing with DMC only, or washing with NMP only. This was done in order to explore the effects of DMC and NMP washing on the anode casting .

[ 0055] With the graphite isolated, a new anode was casted and test batteries were made with the anodes. The basic recipe for virgin graphite consists of 89% graphite, 3% acetylene black (AB an agent to aid in conduction), and 8% PVDF by weight. The recovered graphite was assumed to contain all the AB and most of the PVDF that was cast with it, so only 3% PVDF by weight is added to the recycled graphite slurry. The solid material was then mixed with NMP by a shear mixer that forces the particulates in the solution against two pieces of metal, ensuring that they were reduced in size and evenly dispersed throughout the slurry. The viscosity of the slurry was measured by eye in order to get the best consistency for casting an anode. The target viscosity for virgin graphite slurries is analogous to warm honey, but due to the unique properties of the prelithiated graphite, the slurry was much thinner. The NMP added was based on the weight of the solid material, for every 1 g of anode material 3 mL of NMP was added to the slurry.

[ 0056] In order to make it easier to transfer the copper substrate into a glovebox and onto the anode casting surface, a 10 ]im thick sheet of copper was rolled around a cylinder. The surface was first cleaned thoroughly with NMP in order to remove any contaminants from previous casting. The copper was then carefully rolled out to minimize the formation of bubbles under the substrate, or wrinkles in the copper. An NMP soaked paper towel was then used to rub the top surface of the copper in order to create a surface that is as flat as possible by removing all wrinkles and bubbles. On top of the substrate a tape caster was used so as to create an anode of uniform thickness. The anode was then left to dry overnight.

During the drying process there was a subsequent decrease in thickness based upon the slurry viscosity. For an anode thickness of 80 μπι, the graphite layer should be 65 ]im thick. In order to achieve this, the tape caster was set anywhere between 120 ]im and 150 μπι. The preset thickness used for the tape caster was based on the slurry viscosity. Thicker anodes are preferable as cohesion and porosity of the dried anode can become problematic.

[ 0057 ] After drying, the laminate was removed from the dried anode sheet. The anode sheet was then calendered under a large steel roller to reduce the porosity and increase the anode density. In order to make coin cell anodes, small rounds were punched out of the large calendered anode sheet by pounding a small round hole in

9 . .

the anode sheet using a punch inch m diameter and a hammer. The

16

anode sheet was covered on top and bottom with wax paper in order to minimize the contamination and damage upon punching. The anode rounds were then placed in a vacuum oven and baked at 130 °C for about 16 hours in order to remove any water, solvent and oxygen. After baking, the anodes were ready to be assembled into a coin cell. This process, with the exception of calendaring, can also be done completely in the glove box in order to remove the possibility of oxygen reacting with the lithiated, pre-cycled graphite.

[ 0058 ] The coin cells comprise a face plate, an anode on top of the face plate, and a polymer separator on top of the anode. To the polymer was added 6-8 drops of 1M LiPFe 1:1 EC: DEC (ethyl carbonate : diethyl carbonate) containing an electrolyte solution. A solid lithium metal cathode was stuck to a steel backing plate and placed on top of the polymer. The cell was capped off with a steel separator ring to keep the cell interior pressed together and a rubber O-ring and backing plate to insulate the back and front of the cell electrically. This was all pressed together using argon based hydraulic pump for 30 seconds creating an air tight and electrically insulating seal.

[ 0059] The cells were then tested with battery test equipment

(Maccor Company) . First the cells were put through a formation cycle that had very low current. The initial discharge energized the cell r

to 20 mV at a constant current of— . The cycle was changed to

20

constant voltage at 20 mV until the current reached — C . The charge

40

phase then took the cell to 1.4 Volts at — C . This cycle was

20

r

repeated twice. Another 20 cycles were then performed at — constant

10 r

current to 20 mV and then constant voltage until — for the charge

20

cycle. The discharge cycle was another — C constant current cycle.

20

This cycling protocol allowed for generation of consistent data with respect to first cycle capacity loss and capacity loss over multiple cycles. Data were collected of the cell voltage and current at preset time intervals. The results were compared to a virgin graphite anode that was made using the same method and cycled with the same procedure.

[ 0060 ] The current and voltage values collected by the battery test equipment allowed for the analysis of the quality of the anodes created. It is known that lithium metal has a 3V potential vs.

graphite. By looking at the initial voltage of a newly assembled coin cell, the extent of pre-lithiation can be determined. Since virgin graphite has no lithium in its graphite, the initial voltage should be 3V. As shown in FIG. 2A, the initial voltage of the virgin graphite anode was found to be exactly 3.086 volts. This corresponds to a perfectly lithium free anode with a small internal resistance. As can be seen in the initial voltage graph in FIG. 2B there is some pre-lithiation in the recycled graphite, indicated by the measured 1.2 V initial voltage.

[0061] The capacitance values were calculated by using Maccor software by automatically multiplying the current flowing through the battery by the time that the current has flowed. Since the current was constant for most of the cycling, the amount of time that the cell takes to cycle, gives the capacity of the cell at any point in time. Looking at the initial cycle voltage profile of FIG. 2A it can be seen that it takes approximately 5 seconds for the voltage to drop from 3V to 1.2V. When taken relative to the total amount of time the battery cycles it shows that the extent of pre- lithiation is much less than 1% of the total capacity in the cell. From this it is seen that the extent of pre-lithiation is not enough to affect the initial capacity of the recycled graphite anode significantly.

[0062] Degradation of the cycled graphite is not seen based upon the characteristics of the graph in FIG. 2B. It can be seen that voltage curve undergoes several small bumpy plateaus on its downward trend toward 20 mV. These are characteristics of lithium staging within the graphite matrix, different sets of interstitial sites are being filled in with lithium ions. These staging sites almost exactly replicate the virgin graphite staging seen in FIG. 2A, meaning that the recycled graphite has not become amorphous and shows the same structure characteristics of the pristine new graphite. Even with the laptop battery pack capacity being more than 50% degraded the graphite itself is largely unaffected by the heavy cycling .

[0063] The method for anode production is seen to be quite stable for cycling as shown by the capacity values of virgin graphite anode seen in FIG. 3A. There is a small first cycle capacity loss of around 10% followed by stable cycling with a constant input and output capacity. This shows that the anode is mechanically stable and the anode composition and method used for casting and cell assembly does not negatively affect the properties of the cell. FIG . 3B shows that the cycling characteristics for the recycled graphite almost completely mirror that of the virgin anode. There is a small first cycle capacity loss, followed by stable cycling for the rest of the test. While the mechanical properties of the cell at casting were good, the recycled graphite does show some loss of cohesion after the first two cycles. After the third cycle, the cell has reached a stable capacity, demonstrating that it is not only possible to cycle recycled graphite but it can be done so stably given based upon processing during anode recovery and recasting .

[ 0064 ] By using recovered graphite, it was thought that the previously formed SEI layer would be preserved through recasting and thereby reducing the first cycle capacity loss. Since it was shown that recovered anodes cycled well but still had a first cycle loss comparable to the virgin anodes, the state of the initial SEI remains unclear. One potential explanation for this effect is that the lithium incorporated in the recovered cells had oxidized during the calendering and punching stage of anode processing. In order to remove this possibility, a set of anodes were created that were fully processed under an argon atmosphere. Mechanical cohesion for these cells was problematic, but they were cycled successfully. FIG . 4 shows that the first cycle loss has not been diminished by keeping the anode under argon.

[ 0065 ] In its current charge state, the graphite is not

lithiated enough to show any appreciable effect on the capacity of the recycled graphite cells. With a 1.2V initial voltage, the impact to the total capacity would be less than one percent of the total. By looking at FIG . 2A it is seen that it takes only four seconds at r

a current of — m order to lower the voltage from 3 V to 1.2 V.

20

Based upon the average first cycle lithiation time of 2000 seconds at — C , to see a 10 % change m. the i.ni.ti.al cycle capacitance, the

20

voltage would have to be equal to that of the first cycle voltage after 200 seconds. This means that cell would have to have an initial voltage of 0.6 V to have a higher capacity on the charge cycle than the discharge cycle. In order to see this, the cells would have to be charged before disassembly.

[ 0066 ] A number of embodiments have been described herein.

Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of this disclosure. Accordingly, other embodiments are within the scope of the following claims.

Claims

WHAT IS CLAIMED I S :

1. A method to recover anode and/or cathode materials from one or more charged cells of a battery, comprising:

discharging the battery to about .0-3.5 volts and/or cooling the one or more charge cells to a temperature of high resistivity determined by measuring the aggregate resistivity of a plurality of cells ;

opening the one or more charged cells under a dry atmosphere; separating the anode and cathode material from other battery cell components; and

cleaning, separately, the anode and cathode materials using one or more solvents to remove any contaminants, wherein the cleaned anode materials can then be reused in batteries.

2. The method of claim 1, wherein

The method of claim 1, wherein the cleaning step further comprises cleaning the anode and cathode materials using super-critical CO₂.

3. The method of claim 1 or claim 2, wherein the dry atmosphere has a dew point below -50 °C.

4. The method of claim 3, wherein the dry atmosphere comprises an atmosphere of nitrogen or argon that is devoid of oxygen and water vapor .

5. The method of claim 1, wherein the one or more cells are cooled under a dry atmosphere.

6. The method of claim 1, wherein the one or more solvents comprise a high boiling point polar aprotic solvent.

7. The method of claim 1 or 6, wherein the solvent is dimethyl carbonate (DC), iV-methyl-2-pyrrolidone (NMP) , or a mixture thereof.

8. A method of casting an anode sheet from anode materials recovered from recycled batteries, comprising: making a homogenized slurry comprising a binder agent and the recovered anode material of claim 1;

spreading, spraying, or depositing the slurry over the surface of a thin sheet of conductive material; and

drying the slurry to form an anode sheet.

9. The method of claim 8, wherein the binder agent is

polyvinylidene fluoride (PVDF) .

10. The method of claim 8 or claim 9, wherein the slurry further comprises iV-methyl-2-pyrrolidone (NMP) .

11. The method of claim 10, wherein for every gram of anode material, 1 to 5 milliliters of NMP is added to the slurry.

12. The method of claim 8, wherein the conductive material is a thin sheet of copper.

13. The method of any one of claims 8, 9, 11 or 12, wherein the slurry is dried for at least 12 hours at ambient temperature.

14. The method of claim 8, wherein the method utilizes a tape caster in order to create an anode of uniform thickness.

15. The method of claim 8, wherein the anode sheet has a thickness between 50 ]im to 150 μπι.

16. The method of claim 8, wherein the method is performed under a dry atmosphere.

17. The method of claim 16, wherein the dry atmosphere has dew point below -50 °C.

18. The method of claim 17, wherein the dry atmosphere is an atmosphere of nitrogen or argon that is devoid of oxygen and water vapor .

19. A method of forming battery anodes from an anode sheet, comprising :

cutting or punching out a portion of the anode sheet of claim 8 to generate anodes for use in batteries.

20. The method of claim 19, wherein the anode sheet has been calendered using a roller (s) prior to cutting or punching.

21. The method of claim 19 or 20, wherein the method further comprises heating in vacuo the anodes at an elevated temperature for greater than 12 hours.

22. The method of claim 19 or 20, wherein the anodes are

configured to be used in lithium ion batteries.

23. The method of claim 1, 8 or 19, wherein one or more steps are performed using an automated process.

24. The method of claim 1, 8 or 19, wherein the anode materials comprise graphite.

25. The method of claim 24, wherein the graphite is pre-lithiated .

26. The method of claim 1, 8 or 19, wherein the batteries are in a resistively failed degradation state.

27. The method of claim 1, 8 or 19, wherein the batteries are lithium ion batteries.

28. The method of claim 27, where the lithium ion batteries are from laptops or electric vehicles.

29. An anode material recovered by claim 1.

30. An anode sheet produced by claim 8.

One or more battery anodes produced by the method of claim

32. A battery comprising the one or more battery anodes of claim 31.