KR20240164534A - Method for producing lithium metal directly from lithium brine solution - Google Patents

Abstract

Method(s) and apparatus are provided for directly extracting lithium from a brine solution via a combined solvent extraction and electrowinning process. The method comprises solvent extraction combined with electrodeposition of lithium metal from a non-aqueous solution, and further features solvent regeneration. Recovery of lithium metal directly from brine via a commercially available solvent would significantly reduce the operating and capital costs associated with current molten salt electrolysis processes for lithium metal production.

Description

Method for producing lithium metal directly from lithium brine solution

This application claims the benefit of priority to U.S. Provisional Application No. 63/319,210, filed March 11, 2022, and U.S. Provisional Application No. 63/339,479, filed May 8, 2022, the entire contents of both of which are incorporated herein by reference.

background

1. Technical field

The present disclosure relates generally to a method for preparing lithium metal. More specifically, the present disclosure relates to a method for preparing lithium metal electrochemically deposited directly on a substrate from a brine solution.

2. Description of related technologies

Most of lithium metal and its alloys are currently produced via molten salt electrolysis. This molten salt electrolysis process is performed using a eutectic mixture of lithium chloride and potassium chloride as the electrolyte, a graphite anode, and a stainless steel cathode. KCl is added to the electrolyte mixture to lower the melting point of the KCl-LiCl mixture to ~400-420°C, compared to the melting point of pure LiCl, which is >600°C. This electrolytic process produces molten lithium metal at the cathode with a purity of greater than 97%, because the decomposition voltage of LiCl is lower than that of KCl. Although this process produces high-purity lithium metal, the operating temperature of greater than 400°C makes the process energy intensive, and chlorine gas (Cl ₂ ) produced at the anode is an undesirable byproduct due to its high toxicity. Therefore, there is still a need to develop novel methods for producing high-purity lithium metal.

summation

The present disclosure discloses a method and apparatus for plating lithium directly from an aqueous brine solution having a lithium concentration in the range of 100 ppm to 20,000 ppm at normal ambient temperature via a solvent extraction-electrowinning process. The process comprises performing a lithium selective solvent extraction using a solvent that is immiscible with water, electrowinning lithium from the lithium-impregnated solvent, and then recycling the solvent for additional lithium extraction. The process is unique in that it utilizes electrowinning of lithium metal in the presence of a solvent that is immiscible with water instead of stripping the lithium ions back into the aqueous phase. It should be noted that, unlike base metals, electrowinning lithium from an aqueous phase is not possible due to the high reactivity of lithium metal with water. This approach also simplifies the solvent extraction process because half of the process involving stripping is no longer necessary since the stripping duty is performed by electrowinning. Another advantage of this process is that it does not require fresh water, which is important in remote, extremely arid areas where lithium is mined, such as desert environments and the "lithium triangle" of South America (Argentina, Bolivia, and Chile). Direct electroplating or electrowinning of lithium metal from brine using solvents compatible with lithium salts would significantly reduce the operating and capital costs associated with current lithium metal production methods and would greatly simplify the process. Electrowinning can also be used to selectively extract metal from multicomponent solutions in suitable solvents. The lithium metal deposited on the working electrode substrate in this process can be further purified for use in the fabrication of lithium metal electrodes for primary or secondary lithium metal batteries. This process requires less energy and costs than current state-of-the-art commercial lithium metal production methods that require molten salt electrolysis followed by casting and extrusion of lithium metal ingots.

In one embodiment, the present disclosure discloses a process that requires combining a brine with an additional solvent that is immiscible with water and has a greater affinity for the lithium salt in solution than the major salt impurities, such as sodium chloride, potassium chloride, magnesium chloride and calcium chloride, as well as boric acid. In addition, the solvent has the advantage of having a wide electrochemical stability window. The added solvent should have high solubility in the lithium salt, such as LiCl, be immiscible in the brine solution, and have a wide electrochemical stability window. The brine solution and the additional solvent are mixed to allow the lithium salt to transfer from the brine into the added solvent. The mixture is then allowed to stand to separate, such that the added solvent, now saturated with the lithium salt, and the immiscible aqueous brine, now depleted of the lithium salt, are separated. The lithium salt-loaded solvent is continuously overflowed or underflowed into the electrochemical cell, thereby causing lithium metal to be electroplated onto the cathode substrate. The now lithium-depleted, water-immiscible solvent phase is recycled for subsequent extraction and contacted with a freshly introduced lithium salt-containing brine.

In another embodiment, the present disclosure provides a process wherein solvent extraction of lithium chloride can be performed using a solvent having lithium salt selectivity for hydrometallurgical separation combined with a lithium brine solution. The brine solution and an additional solvent are mixed to allow lithium salt to be transferred from the brine to the added solvent. This solvent is then contacted with a second solvent having the desired properties for lithium electroplating to allow lithium to be transferred to the second solvent. This second solvent having the solvated lithium salt can be extracted and used in an electrochemical cell to allow lithium metal to be plated onto a cathode substrate. Both the first and second depleted solvents are recycled.

In another embodiment, the present disclosure provides a process whereby a cation exchange membrane can be used to assist in the transfer of lithium ions from a concentrated lithium brine solution to an alternative solvent medium to be plated as lithium metal on an electron conductive substrate.

So that the features, advantages and objects of the disclosure, as well as others that may become apparent, may be achieved and more particularly understood, the invention, briefly summarized above, may be described with reference to embodiments thereof, which are illustrated in the accompanying drawings that form a part of this specification. It is to be borne in mind, however, that the drawings illustrate only illustrative embodiments of the invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
Figure 1 schematically illustrates one embodiment of the disclosed method for obtaining lithium metal directly from a lithium brine solution via a combined approach of solvent extraction and electrowinning.
Figure 2 shows a schematic diagram of an electrochemical cell used in an electrowinning process for plating lithium metal directly onto a cathode substrate from a solution consisting of a lithium salt in a solvent.
Figure 3 shows an optical photograph of the basic three-electrode cell schematically illustrated in Figure 2.
Figure 4 shows an optical photograph of the interior of the three-electrode cell shown in Figure 3.
Figure 5 shows an optical photograph of the overall basic device configuration to support the concept. The device configuration consists of a three-electrode cell connected to a potentiometer to control the electrochemical parameters during the lithium electrowinning process.
Figure 6 shows the voltammograms (or current-voltage curves) obtained during the electrodeposition of lithium metal onto a copper cathode in an electrochemical cell containing a 1 M LiPF ₆ -DEC solution as an electrolyte. Here, DEC is a solvent that dissolves LiPF ₆ lithium salt, which has low water miscibility (<4 wt%).
Figure 7 shows a voltammogram for lithium metal electrodeposition at a fixed voltage and the resulting lithium metal deposited on a copper-plated platinum cathode in an electrochemical cell.
Figure 8 shows the electrochemical cell of Figure 3 after lithium metal has been electrodeposited on a copper substrate.
Figure 9 shows the voltammograms (current versus voltage curves) obtained during the electrodeposition of lithium on a copper substrate. The lithium salt used during these measurements was LiPF ₆ and the solvent was diethylene carbonate. The concentration of the salt in the solvent was 1 M LiPF ₆ in DEC. This salt solution in solvent was used for demonstration purposes.
Figure 10 shows a current versus time plot for another run of lithium deposition from solution at a constant potential of 4 V versus a Ag/AgCl reference electrode. This voltage was chosen after observing the plating voltages observed in the voltammogram of Figure 9.
Figure 11 shows an optical photograph of the results of an electrodeposition experiment performed to obtain the current versus time plot of Figure 10. The left strip shows the copper cathode substrate before the experiment. The right strip shows lithium metal deposited on the copper cathode substrate after the electrodeposition process.
Figure 12 shows a schematic diagram of one embodiment enabling the deposition of lithium metal directly from a brine, assisted by a cation exchange membrane that allows only lithium ions to transfer from the lithium brine phase to the lithium salt in the solvent phase, where they can then be electrodeposited on the cathode substrate.
Figure 13 shows a cyclic voltammogram for a lithium metal plating experiment performed on the basic cell schematically illustrated in Figure 12.
Figure 14 illustrates a process for performing lithium extraction and electroplating simultaneously.
Figures 15a and 15b illustrate a demonstration device for preparing simultaneous lithium extraction and electroplating, including a cell schematic.
Figure 16 illustrates a cell process including a sandwiched liquid membrane.
Figure 17 shows a schematic diagram of a processing cell for continuous R2R production of lithium from aqueous brine.
Figure 18 shows a schematic diagram of a treatment cell for depositing a lithium metal film on a Cu foil moving from an organic solution medium.
Figure 19 shows the design structure of the electroplating cell.

Detailed description of the embodiment

The method and system of the present disclosure will now be described in more detail hereinafter with reference to the accompanying drawings which illustrate embodiments. The method and system of the present disclosure may take many different forms and should not be construed as limited to the illustrative embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers represent like elements throughout.

Direct lithium extraction (DLE) from brine is a challenging task. The most abundant lithium brine resources on Earth, such as those in the South American "lithium triangle" (Argentina-Bolivia-Chile), are concentrated brine with high total dissolved solids levels. These lithium brines are nearly saturated mixed salt solutions containing salts of cations (primarily Li ⁺ , Na ⁺ , K ⁺ , Mg2 ⁺ , Ca2 ⁺ , B ^+, and H ⁺ ) and salts of anions (primarily ^Cl- , _SO42- , and ^OH- ) ^. Most direct lithium extraction technologies use fresh water to leach lithium from adsorbents or to strip lithium from lithium-selective solvents. However, the regions where direct lithium extraction is performed are extremely dry, making it more difficult to apply.

The demand for lithium metal is expected to be high because future high-capacity batteries are expected to use lithium metal anodes. The current global lithium metal production is very small, and the gap between demand and supply is expected to be large. The present disclosure proposes a novel, significantly reduced cost method for producing lithium metal without using fresh water. This is achieved by solvent extraction (SE) integrated with a novel electrodeposition (ED) method as illustrated in FIG. 1.

In the disclosed method for producing lithium metal directly from a lithium brine, lithium ions in the brine are selectively extracted into an added solvent medium by solvent extraction or membrane-assisted solvent extraction. The lithium ions are then electrochemically deposited on an electron-conducting substrate from the final lithium-impregnated organic or inorganic solvent medium in a process known as electrowinning. The process may also be performed by a series of solvent extraction steps before the lithium metal is electrowinning from the organic or inorganic solvent medium onto the electron-conducting substrate. Lithium salts that can be used to electrodeposit lithium include, but are not limited to, LiCl, LiClO ₄ , Li ₂ SO ₄ , or LiPF ₆ . The final purity of the lithium deposited by the overall process starting from a lithium brine can range from 80 to 99.99%. The final thickness of the lithium metal plated from the starting concentrated brine solution can range from 1 nm to 5 mm. The solvent must have several key characteristics to be integrated into the disclosed process: (1) the solvent must be highly solubilizing or selectively extractable from the aqueous brine of dissolved Li ions/salts; (2) the solvent must allow for cathodic deposition of Li metal; (3) the solvent must have long-term stability to withstand anode reactivity degradation during processing in the electrochemical cell; and (4) the solvent must be immiscible with water. In the case of membrane-assisted solvent extraction, the membrane will selectively permeate lithium from the brine into the added solvent.

The lithium metal product obtained in the above process can be further purified to serve as an anode material in primary or secondary batteries in which metallic lithium serves as at least one electrode. In such battery chemistries, viable metallic lithium metal electrodes can be prepared for batteries including but not limited to lithium-oxygen batteries, lithium-sulfur batteries, rechargeable lithium metal batteries having lithium-ion insertion cathodes, lithium-MnO ₂ primary batteries, and solid-state lithium metal batteries comprising a solid-state lithium-ion conductor as the electrolyte as opposed to a liquid electrolyte having a solvated lithium-ion conducting salt.

Battery-grade lithium metal requires additional steps of purification after lithium metal ingot is prepared by molten salt electrolysis to obtain lithium metal with purity >99.8% necessary for secondary battery operation, and further steps for fabrication of lithium metal electrodes to be used in secondary batteries. The disclosed technology can avoid the purification steps and electrode fabrication steps to directly produce battery-grade lithium metal in the form of electrodes. The lithium metal electrodes prepared by the disclosed method can have a size of 1 nm to 5 mm. The process can be performed in a roll-to-roll manner to produce full commercial-scale rolls of lithium metal plated on copper electrodes for use in the commercial fabrication of lithium metal secondary batteries, thereby limiting the number of process steps and further reducing the cost of manufacturing lithium metal electrodes for relevant battery chemistries.

A. Device for performing separation

FIG. 14 illustrates a solvo-electro-deposition process (100) for forming a lithium membrane. In one embodiment, the solvo-electro-deposition process (100) can include providing an aqueous brine (102), forming a pure Li-containing aqueous solution (e.g., LiCl (lithium chloride)) (104A), electrodepositing lithium from an organic solution medium (104B) (e.g., membrane-assisted), and forming a Li-metal membrane deposit (106) (e.g., for a battery anode). In an alternative related embodiment, the solvo-electro-deposition process (100) can include the steps of providing an aqueous brine (102), electrodepositing lithium directly from an organic solution medium (104C) (e.g., membrane-assisted), and producing a dark gray Li-metal film deposit (106) (e.g., for a battery anode).

In connection with FIG. 14 , FIGS. 15a and 15b illustrate a batch-cell system (120) for use in connection with one embodiment depicted in FIG. 14 . FIG. 15a is a photographic representation of a laboratory-demonstration version of a processing cell (e.g., batch cell) system (120) and associated solvo-electro-deposition process (100) for performing simultaneous lithium extraction and electrodeposition, in connection with the embodiment associated with FIG. 14 . FIG. 15b is a graphical representation of the batch-cell system shown in FIG. 15a . A batch-cell system (120) can include a cell containment unit (122) (e.g., a vessel that can include a liquid electrolyte and can hold, for example, electrodes and/or membranes), a working electrode (124) (e.g., a cathode made of, for example, copper or another metal), a counter electrode (126) (e.g., an anode made of, for example, mixed metal oxide (MMO) or platinum (Pt)), a reference electrode (128) (e.g., to aid in measuring a reference conductivity), and a metal foil (130) (e.g., made of copper). During electrodeposition, the resulting composite metal foil (130A) can include the base metal foil (130) and the lithium layer (132). As further shown in FIG. 15b, the treatment cell (e.g., batch cell) system (120) can further include an anode chamber (136) containing a membrane (134) (e.g., a CEM or selective cation exchange membrane (sCEM)); and a Li ⁺ -containing aqueous brine (e.g., derived from a storage tank/container, a lake, a pond, and/or a well) and a cathode chamber (138) containing a Li-X (salt) solvent organic solution medium. In one embodiment, the respective boundaries of the anode chamber (136) and the cathode chamber (138) can be defined at least in part by the cell containment unit (122) and the membrane (134). In one embodiment, the membrane (134) can be positioned between the working electrode (124) and the counter electrode (126). The counter electrode (326) and the working electrode (324) can be configured to be charged in a manner that drives the electrodeposition of lithium onto the metal foil (330/330A) extending through/into a lithium-containing organic solution (e.g., within the cathode chamber (138)). In one embodiment, the treatment cell (120) can define a galvanic cell. In one embodiment, the counter electrode (126) can be in contact with the Li ⁺ -containing aqueous brine in the anode chamber (136), and the working electrode (124) can be in contact with the lithium-containing organic solution in the cathode chamber (138). In one embodiment, the cell containment unit (122) can be defined as a housing and/or container.

FIG. 15b illustrates a laboratory demonstration example of the batch cell process of FIG. 14 in which a Li metal layer (132) (from an organic solvent Li-X solution) can be electrodeposited on a plate or foil cathode (130) (e.g., copper) while at the same time allowing an organic solution medium (e.g., a lithium-containing organic electrolyte solution) in the cathode chamber (138) to extract lithium from an aqueous solution or brine in the anode chamber (136). A Li+-conductive or Li+-selective membrane (134) can be positioned centrally between the organic and aqueous solutions (see FIG. 15b ). Such an extraction-electrodeposition cell (120) can be configured to have two chambers (136, 138) defined by a cell containment unit (122) and an intermediate membrane (134). One chamber (136) may contain an aqueous brine solution, and the other chamber (138) may contain an organic solution. Additionally, each solution may be replenished, as needed, from an external storage tank and/or a natural source (e.g., a lake, pond, aquifer, and/or well), the lake (102) illustrated in FIG. 14 being one example of such a replenishment source. The process (100) of FIGS. 15a and 15b may be considered a solvo-electroextraction-electrodeposition process in a single-unit treatment cell (120). Depending on the cell dimensions, configuration, and solution type (brine and organic solution), the current density for the two-electrode electrodeposition may range from 0.1-100 mA per cm ² of membrane or cathode surface area. During fixed current electrodeposition, the operating voltage can be between 0 and 10 V (which includes the Li reduction potential and IR drop of ~3.2 V vs. Ag/AgCl (KCl) reference electrode).

FIG. 16 illustrates a derivative cell configuration according to an embodiment of the present disclosure. The derivative cell configuration, generally labeled as a processing cell (220), can include a cell containment unit (222), a working electrode (224) (e.g., a cathode made of, for example, copper or another metal), a counter electrode (226) (e.g., an anode made of, for example, mixed metal oxide (MMO) or platinum (Pt)), a reference electrode (228), a composite metal foil (230A) (e.g., made of copper and coated with a lithium layer), a Li-X solvent liquid membrane (234) (e.g., comprising a pair of CEMs and an intermediate solvent zone (not individually labeled)), an anode chamber (236) holding a Li+-containing aqueous brine, and a cathode chamber (238) holding a Li-X solvent organic solution medium. It should be understood that throughout this disclosure, like-numbered components (e.g., 120, 220, 320, and 420; 124, 224, 324, and 424, etc.) can be expected to be similar in function and/or design, unless specifically stated otherwise in a given embodiment.

Comparing FIGS. 15b and 16, the central membrane (134) (CEM or optional CEM) within the two-chamber cell (120) of FIG. 15b can be replaced with a sandwiched liquid membrane or liquid chamber (234) as shown in FIG. 16. The sandwiched liquid membrane (234) can comprise a Li-X solvent sandwiched between two solid Li-conducting membranes or CEMs (components not individually labeled). The liquid membrane (234) can provide Li ⁺ selectivity for permeation from the aqueous solution in the anode chamber (236) to the organic solution in the cathode chamber (238). Thus, FIG. 16 illustrates a treatment cell (220) for a solvo-electroextraction-electrodeposition process in a single-unit configuration that can selectively transport Li ions from the aqueous brine in the anode chamber (236) to the organic solution medium in the cathode chamber (238) by utilizing sandwiched liquid membranes (234). When the liquid in the central chamber recirculates the liquid membrane (234) through the outer loop of the dehydration column, the liquid membrane (or chamber) can act as a barrier to block the transport of water molecules from the aqueous brine chamber to the organic solution chamber (while allowing the transport of Li). This will aid in continuous operation where extraction and deposition are performed simultaneously.

FIG. 17 illustrates an embodiment of a processing cell (320) that aids in the industrial mass continuous production of Li metal film deposits on a substrate foil (e.g., copper foil or other metal film or web) while extracting lithium from an aqueous brine, for example, using a roll-to-roll (R2R) facility. As illustrated in FIG. 17, the treatment cell (320) comprises a cell containment unit (322) (e.g., a vessel that may contain a liquid electrolyte and may hold, for example, electrodes and/or membranes), a working electrode (324) (e.g., a cathode made of, for example, copper or another metal), a counter electrode (326) (e.g., an anode made of, for example, mixed metal oxide (MMO) or platinum (Pt)), a reference electrode (328) (e.g., typically positioned close to (within a few millimeters) the cathode surface), a metal foil (330) (e.g., copper foil), a composite metal foil (330A) (e.g., made of copper coated with a lithium layer), a membrane (334) (e.g., a CEM or sCEM), an anode chamber (336) containing a Li ⁺ -containing aqueous brine, a brine source (336A) used in the anode chamber (336) (e.g., a The cell may include a cathode chamber (338) holding a Li-X solvent organic solution medium (e.g., a lake, a well, an aquifer, and/or a storage container), an input/feed foil roll (340A), a product foil roll (340B) (e.g., lithium-coated copper foil), a storage tank (342) (e.g., which may have the product foil roll (340B)) filled with an inert gas (e.g., argon (Ar)), and a dehydration column (344) (e.g., a zeolite dehydration column bed). In embodiments, the membrane (334) may be positioned between the working electrode (324) and the counter electrode (326). The counter electrode (326) and the working electrode (324) may be configured to be charged in a manner that drives the electrodeposition of lithium onto the extended metal foil (330/330A) through the lithium-containing organic solution. The processing cell (320) may additionally include connecting conduits and/or one or more additional intermediate rollers (illustrated but not labeled) to facilitate fluid movement/replenishment and/or foil movement, as desired.

The roll-to-roll processing cell (320) of FIG. 17 can facilitate a continuous multi-step deposition process. In a first step, the aqueous brine solution within the anode chamber (336) can be replenished from an external source or reservoir (336A), as needed, to continuously provide Li ⁺ . In a second step, Li ⁺ can be continuously transferred from the aqueous phase to the organic phase through the membrane (334). In a third step, while the Cu foil web (330, 330A) is continuously moved through the electrodeposition zone, electrodeposition of Li metal onto a moving copper cathode (324) (e.g., in the form of copper foil (330) supplied from a supply foil roll (340A)) can occur in the cathode (e.g., organic solution) chamber (338). The water content level of the organic phase can be controlled by a dehydration column (344) and an associated recirculation loop. According to the fourth step, the product roll (340B) of Li metal-Cu foil web (330A) can be preserved and/or stored in an inert gas chamber (342) provided with an argon (Ar) gas atmosphere or another suitable inert gas, together with any hardware necessary to facilitate collection of the product roll (340B).

FIG. 18 illustrates a roll-to-roll (R2R) cathode deposition process for depositing a lithium (Li) metal film on a metal (e.g., copper) foil web moving through an organic solution, according to an embodiment of the present disclosure. The R2R cathode deposition process can be accomplished using a roll-to-roll (R2R) processing cell (420). An R2R processing cell (420) can include a cell containment unit (422), a working electrode (424) (e.g., a cathode made of, for example, copper or another metal), a counter electrode (426) (e.g., an anode made of, for example, mixed metal oxide (MMO) or platinum (Pt)), a metal foil (430) (e.g., copper foil), a composite metal foil (430A) (e.g., made of copper coated with a lithium layer), a cathode chamber (438) holding a Li-X solvent organic solution medium, an input/feed foil roll (440A), a product foil roll (440B) (e.g., lithium-coated copper foil), a storage tank (442) filled with argon (Ar) gas (e.g., which may have a product foil roll (440B)), and a dehydration column (444). The counter electrode (426) (e.g., anode) and the working electrode (424) (e.g., cathode) can be configured to be charged in such a way as to drive the electrodeposition of lithium onto the extended metal foil (430/430A) via the lithium-containing organic solution. Note that unlike the system (320) illustrated in FIG. 17, since the organic Li-containing solution serves as the Li source instead of brine, the R2R treatment cell (420) may not include, for example, a separate anode chamber and/or membrane. Instead, both the anode (426) and the cathode (428) are contained within the same chamber (e.g., 438), thereby simplifying the construction relative to the system (320) of FIG. 16.

Moreover, with respect to FIG. 18, where one or more lithium-containing organic solutions serve as the Li source, a R2R cathode deposition process using a roll-to-roll (R2R) processing cell (420) may be utilized, thereby simplifying the R2R setup as discussed above. In such a case, the water content of the organic solution for the electrodeposition zone (e.g., 438) for the moving cathode (424) (e.g., metal (e.g., Cu) foil web (430); and composite (e.g., Li-Cu) foil web (430A)) may be controlled to minimize the dissolution rate of the deposited Li metal (not individually labeled). Additionally, more Li-containing organic solution may be continuously fed to the electrodeposition tank/chamber (438) during continued continuous manufacturing. To minimize anode degradation and extend the life of the organic medium, the immobilized anode (426) may be positioned outside of the organic solution and/or the anode (426) may be modified with one or more coating materials (e.g., LFP (lithium iron phosphate)). Additionally, other additives (e.g., ionic liquids) may be added to or otherwise utilized in the organic phase to enhance Li-X salt solubility and improve electrodeposition performance. For example, to enable liquid Li metal electrodeposition and recovery around the cathode, the ionic liquid (organic phase) may be heated to a temperature slightly above 180° C. (i.e., the melting point of Li metal).

In an embodiment, the linear velocity of the driven copper web (v), the applied electrical deposition current (i), the width of the lithium layer being deposited (w), and the current efficiency of lithium deposition (η) can have the following relationships:

Q = iη/vw Equation 1

Here, Q is the total charge passing through. Q is related to the amount of lithium metal deposited on the cathode surface. For example, in the case of lithium with a single positive charge, each charge corresponds to a single lithium atom.

The electrochemical deposition time can be defined by the following equation:

t = η/vw Equation 2

In order to deposit useful lithium metal on a battery anode, it may be important to control the plating current density and thickness. In an embodiment, the lithium deposition rate can be controlled at a current density in the range of 0.2 mA/cm ² to 0.8 mA/cm ² and a thickness range equivalent of 1 mAh/cm ² to 100 mAh/cm ² , where mA = milliamp; cm = centimeter; and h = time. Given the above, since each charge corresponds to a single lithium atom, the thickness range equivalent can be considered proportional to the thickness produced. Using the two ranges, the electrodeposition time can be calculated using Equations 1 and 2. For example, when plating a total equivalent of 100 mAh/cm ² of Li at a rate of 0.2 mA/cm ² , the total deposition time converts to 500 hours. Depending on these Li electroplating conditions, the deposition time can range from, for example, 1.25 to 500 hours, depending on the selected parameters and the desired thickness/thickness equivalence.

In one embodiment, a design with increased overlap of the cathode and anode can allow for long electroplating times while still allowing for reasonable linear manufacturing rates. It should be appreciated that various design structures can be used to achieve electroplating conditions. FIG. 19 illustrates one such design for electroplating, which design features an extended overlapping surface area for the two electrodes. The R2R processing cell (520) can include, similar to the R2R processing cell (420), a cell containment unit (522), a working electrode (524) (e.g., a cathode made of, for example, copper or another metal), a counter electrode (526) (e.g., an anode made of, for example, mixed metal oxide (MMO) or platinum (Pt)), and a metal foil (530) (e.g., copper foil). Unlike the R2R processing cell (420), the R2R processing cell (520) can additionally include a series of intermediate transport rolls (540C) holding the metal foil (530). The intermediate transport roll (540C) may be configured to facilitate the definition of a plurality of foil sections (e.g., two of which (530A and 530B) are labeled), wherein a given foil section may be defined between an adjacent pair of intermediate transport rolls (540C). The foil sections together may define a plurality of adjacent foil sections, e.g., (530A) and (530B). Additionally, a given counter electrode (526) may be considered to be an anode and may include/define a plurality of anode extensions, one of which is labeled (526A) (i.e., defining a multi-branch anode (526)). Each anode extension can extend between a pair of adjacent foil sections (e.g., anode extension (526A) between foil sections (530A) and (530B)) that together define a given electroplating zone (Z), which multiple electroplating zones (Z) can be defined by the R2R treatment cell (520). The electrode surface overlap area (A) can facilitate an increase in plating amount and/or can allow for a faster linear rate v in Equation 2. In embodiments, the R2R electroplating process facilitated by the R2R treatment cell (520) can enable a lithium electroplating reaction time in the range of, for example, 0.5 to 1000 hours, 5 to 400 hours, or 20 to 300 hours. In an embodiment, the large surface area overlap (A) associated with the R2R treatment cell (520) can extend into a mass transport window, where ion transport in the electrolyte is driven by the multiple anodes (526).

It should be noted that the processing cell configuration is not necessarily limited to the exemplary design depicted in the above-described drawings. In addition to changes in the organic solution handling, the electrode design and material types may be readily modified for better performance, and such modifications are considered to be within the scope of the present disclosure. Additionally, it should be understood that the components described in connection with the various embodiments may be mixed and/or mated with one another, unless expressly excluded. Additionally, while copper has been discussed as a candidate material for lithium electrodeposition, it should be understood that other conductive metals or metal alloys may serve as suitable substrates for lithium deposition.

In summary, one or more embodiments of the present disclosure may result in (1) a roll-to-roll Li metal membrane (battery anode) fabrication technology; and/or lithium-metal fabrication and lithium-ion extraction technology from aqueous or organic solutions. The integrated hybrid solvo-electro-processing enables simultaneous lithium extraction and metal fabrication in a single-step batch or continuous operation. The "solvo-processing" may utilize the organic solution as a Li ⁺ -transport medium suitable for electrodeposition or as a solvent(s) for selective extraction of lithium from aqueous brine. In the former case, a Li ⁺ -selective membrane (solid CEM or liquid) between the aqueous and organic phases may add Li ⁺ -transport selectivity for DLE (direct lithium extraction) from the source brine. The "electro-processing" of the present disclosure may utilize electrically enhanced electrodialysis rates (for lithium extraction and transport mobility) and/or electrodeposition rates (for Li metal membrane fabrication). Aqueous-organic two-phase electrodialysis can be uniquely implemented to extract/transport lithium from aqueous brine/solution to organic solution media. With respect to competing electrowinning processes for Li metal production, the present technology can (1) provide a less costly option for the production of Li metal films as battery anodes (<20 μm thick); and/or (2) provide simultaneous DLE and Li metal film electrodeposition from aqueous brine in a single integrated process.

The present technology may be characterized by one or more features. The technology may allow for the simultaneous combination of Li extraction (from an aqueous brine) and production of Li metal (battery anode) in a continuous process that does not require treatment water. The process may be operated in roll-to-roll (R2R) or batch mode for the production of Li metal (via electrodeposition of Li from an organic phase) and/or for continuous lithium extraction from an aqueous brine. The technology may implement an organic phase as an electrodeposition medium (e.g., an organic solution obtained by solvent extraction) which may be lithium salt-soluble or lithium ion-selective. The system may be characterized by a dehydration process that controls the water content of the organic phase to allow for continuous electrodeposition of Li metal with better current efficiency and/or better quality of the Li metal fill deposit. An associated process may result in faster direct lithium extraction (DLE) rates from an aqueous brine due to a larger Li ⁺ concentration gradient between the aqueous and organic phases driven by the electrodeposition phenomenon. The integrated process may utilize phenomena similar to electrodialysis for faster ion mobility and/or transport from aqueous to organic phases. The system may allow for lower temperature (e.g., room temperature and/or ambient temperature) and lower cost processing than molten-salt electrowinning. An R2R version of the system and method may be used to directly produce thin film deposits of Li metal on copper foil webs, which may be used, for example, as a suitable platform for Li battery anodes.

The following are examples to support the principle, providing methods and specific conditions that enable lithium metal electrodeposition from solvent-extracted solutions. The present invention is in no way limited to these examples.

Example 1: Lithium deposition from organic solvents using LiPF ₆ as an ion conducting salt

Figure 2 shows a schematic diagram of a three-electrode electrochemical cell used for the electrodeposition of lithium metal, consisting of a working electrode (cathode, e.g., copper, copper-plated platinum, or another electron conducting substrate), a reference electrode (e.g., Ag/AgCl), and a counter electrode (anode). A precise experimental cell for demonstrating direct electrowinning of lithium metal from a solvent medium having a solvated lithium salt is shown in Figure 3.

Specifically, in one embodiment, the electrochemical cell uses a cathode copper rod as the working electrode, the sides of which are electrically insulated so that only a well-defined circular flat surface (0.5 cm ² ) at the bottom is exposed to the electrolyte solution. A glass encapsulated reference electrode (Ag/AgCl (1 M KCl)) face (<1-mm gap) is used as the reference electrode. A platinum foil ring anode is arranged concentrically at the bottom of the electrodeposition cell and serves as the counter electrode. The components specified above are illustrated in FIG. 4 for clarity. It should be noted that the electrochemical cell design and electrode types (geometry, type of material, and dimensions) are not limited to these examples in terms of geometry, physical dimensions, or material composition. The overall experimental setup for the electrochemical cell and lithium metal electrowinning process is illustrated in FIG. 5 .

Figure 6 shows the voltammograms obtained during the initial linear sweep voltammetry experiments to determine the plating voltage of lithium metal on a copper current collector in the experimental setup depicted in Figure 5, having the experimental cell illustrated in Figure 3. The electrolyte solution for this demonstration was 1 M LiPF ₆ in diethyl carbonate (DEC). The reduction-oxidation (redox) reaction was observed to occur at about -2.8 V vs. Ag/AgCl reference electrode, as evidenced by a dramatic increase in the absolute value of the measured current of the electrochemical cell. This initial onset of the current increase is due to the decomposition of the DEC solvent, which is known to have a limited electrochemical stability window. The secondary redox reaction starts at about 3.2 V vs. Ag/AgCl, which is due to the initiation of electrochemical plating of lithium. The potentials for these observed lithium depositions are in good agreement with the thermodynamically predicted potentials for this reaction from the standard reduction potential table, i.e., the difference between the standard reduction potential of lithium metal and the standard reduction potential of a Ag/AgCl reference electrode (-3.045 V - 0.2223 V = -3.2673 V). This agreement between the experimentally observed potentials and the thermodynamically predicted potentials is a preliminary indication that lithium metal can be electrowinning from solution. For reference, the relevant standard reduction reactions and the corresponding potentials for the standard hydrogen electrode (SHE) are provided.

Li ⁺ + e ^- → Li - 3.045 V (cathode reduction reaction for Li metal deposition)

AgCl + e ^- → Ag ⁺ + Cl ^- 0.2223 V (reference electrode, Ag/AgCl (1M KCl))

2H ⁺ + 2e ^- → H ₂ 0.00 V (standard hydrogen electrode, SHE)

To produce meaningful amounts of metallic lithium, chronoamperometric experiments were performed, in which the voltage of the electrochemical cell was held constant and the current was recorded as a function of time. The results of these experiments are shown in Fig. 7. During these measurements, the voltage of the cell was held constant at -3.5 V vs. the Ag/AgCl reference electrode. An optical photograph of the electrochemical cell is shown in Fig. 8, which shows that a large gray solid deposit has formed on the copper working electrode. The gray deposit was recovered and washed with N-methyl pyrrolidine (NMP) for analysis. A quick test to determine whether the gray deposit contains metallic lithium is to immerse the solid in water. Metallic lithium reacts violently with water via the reaction Li(s) + _H2O (l) → LiOH(l) + _H2 (g). The solid deposit recovered from the chronoamperometric experiment was immersed in deionized water, and gas bubbles immediately formed, which may be due to the evolution of hydrogen gas. Additionally, the gray solid gradually dissolved away, exposing the copper substrate underneath. The water used for immersion was analyzed using ICP to determine the amount and confirm the presence of Li. Based on the amount of lithium recorded, it was estimated that a lithium layer of 2-7 micrometers was deposited in various experiments. The current efficiency was calculated to be in the range of 60-80%.

In the subsequent electrodeposition step, dendritic lithium metal is formed (Fig. 5). The faradaic efficiency for this lithium metal electrodeposition process is calculated to be 61%. In principle, the rate of lithium metal deposition on the cathode surface (mg/s) can be controlled by varying the voltage and current applied in the electrochemical cell. One form of Faraday's law is as follows:

m/MW = [I t]/[n F]

where m = mass of deposited species (g), MW = molecular weight of deposited species, I = current (ampere), t = time (s), n = electron equivalent/mole, and F = Faraday's constant (96,485.3 C/eq or A-s/eq). For the lithium metal deposition process described herein, MW is 6.941 g/mole and n = 1 electron/mole. The other values in the equation are experimentally measured, experimentally applied, or are physical constants.

To determine the lithium plating or lithium deposition rate, the equation can be rewritten as:

m/t = [I MW]/[n F]

If I is not known but m/t is known, the equation can be rewritten once more to find the required current that must be applied to obtain the desired deposition rate:

I = [m/t n F]/MW

This final formula can be used to control the deposition rate during the process described in the present invention to obtain a lithium metal electrode of a desired thickness for use in primary or secondary lithium metal batteries.

Example 2: Demonstration of the scalability of lithium metal electrowinning for commercial lithium metal electrode production

In the previous examples, the copper rod cathode surface had a limited surface area (0.5 cm ² ) for lithium deposition. To enlarge the surface area for cathodic electrodeposition of Li metal, a long copper strip rather than a single section of copper rod was used as the working electrode. This copper strip had an electrochemically active surface area more than ten times larger than that of the copper rod used in the original lithium electrowinning experiments. This enlargement of the working electrode demonstrates the scalability of this approach for commercial applications requiring lithium deposition on copper substrates up to 3 meters wide in a roll-to-roll manner.

As in the previous examples, experiments were performed on this larger copper substrate working electrode to support a similar concept. A linear sweep voltammogram is presented in Figure 9 showing the onset potential of lithium metal deposition similar to the smaller electrowinning experiments. Figure 10 shows a current versus time plot for a chronoamperometric experiment performed using the larger copper working electrode in the electrowinning cell. For these measurements, the cell voltage was maintained at -4 V versus the Ag/AgCl reference electrode. The voltage in this example was higher than that in Example 1 to overcome any kinetic barrier that may arise due to the larger electrochemically active surface area of the cathode in this case. As in Example 1, the electrochemical cell for electrowinning lithium metal from the solvent medium consisted of a Ag/AgCl reference electrode, a platinum counter electrode, and 1 M LiPF ₆ in DEC as the electrolyte. Visual confirmation of lithium metal deposition on the larger copper working electrode is provided in Figure 11 showing the copper substrate before and after the electrowinning process.

The disclosed method for producing lithium metal from brine can be readily modified to utilize existing commercial electroplating or electrowinning equipment or components. The electrowinning cell can utilize roll-to-roll anode deposition to deposit lithium metal over a large surface area on a substrate surface that is immersed in and pulled through a plating electrolyte medium. An example of such an embodiment can include plating lithium metal on a copper foil substrate by rolling the copper foil through a liquid lithium electrolyte medium. Some existing commercial electrodeposition cells, such as industrial electrowinning or electroplating cells, can be modified and adapted for this room temperature hybrid solvent extraction and electrowinning process.

Example 3: Membrane-assisted lithium metal production from concentrated lithium brine

One embodiment of the appended method allows for the use of a cation exchange membrane to assist in the separation of lithium ions from a concentrated lithium brine into an alternative solvent medium and then plating lithium metal therefrom. An electrochemical cell that can be used in this process is schematically illustrated in FIG. 12. In this cell, lithium ions are electrochemically driven from a concentrated lithium brine through a lithium ion selective cation exchange membrane into a solvent medium and then finally plated onto a metal substrate used as a cathode in the cell. A cyclic voltammogram for this electrochemical cell is provided in FIG. 13. The electrochemical cell used in this experiment consisted of a copper substrate cathode, a platinum anode, a concentrated lithium brine as an anolyte, a lithium conductive salt solvated in a solvent as a catholyte, and a cation exchange membrane as a separator between compartments containing two different electrolyte media. Although these experiments suggest the reversibility of the process, in practice, the concentrated lithium brine is continuously replenished to provide a constant source of lithium ions to drive the operation of the cell. As with Example 2, this process can be modified to be a continuous roll-to-roll process.

The description, including the summary, brief description of the drawings, and the detailed description, and the appended claims, relate to specific features of the disclosure (including process or method steps). Those skilled in the art will understand that the invention includes all possible combinations and uses of the specific features described in the description. Those skilled in the art will understand that the disclosure is not limited to or by the description of the embodiments given in the description.

Those skilled in the relevant art will also understand that the terminology used to describe specific embodiments does not limit the scope or scope of the disclosure. When interpreting the specification and the appended claims, all terms should be interpreted in the broadest possible manner consistent with the context of each term. All technical and scientific terms used in the specification and the appended claims have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs, unless otherwise defined.

The singular forms used in the specification and the appended claims include plural referents unless the context clearly dictates otherwise. The verb "comprises" and its conjugations should be construed as referring to elements, components, or steps in a non-exclusive manner. The elements, components, or steps mentioned may be present, utilized, or combined with other elements, components, or steps not explicitly mentioned. The verb "operatively connecting" and its conjugations mean completing any type of connection, including electrical, mechanical, or fluidic connections, necessary to form a connection between two or more objects that were not previously connected. When a first component is operatively connected to a second component, the connection may occur directly or through a common connection. "Optionally" and its various forms mean that the subsequently described event or circumstance may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not.

Conditional language, such as, among others, "may," "could," "might," or "should," unless specifically stated otherwise or understood from the context in which it is used, is generally intended to convey that some implementations may include particular features, elements, and/or actions while other implementations do not. Thus, such conditional language is not generally intended to imply that the features, elements, and/or actions are in any way required for one or more implementations, or that one or more implementations necessarily include logic for determining whether such features, elements, and/or actions are to be included or performed in any particular implementation, with or without user input or prompting.

Therefore, the system and method described herein are well suited to carrying out the purpose and achieving the stated objectives and advantages, as well as others inherent therein. While exemplary embodiments of the system and method have been given for the purpose of disclosure, there are numerous variations in the details of the procedures for achieving the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art and are intended to be included within the scope of the present disclosure and appended claims of the system and method disclosed herein.

Claims (46)

A method for producing lithium metal,
(A) a step of extracting a lithium brine with a solvent to obtain a lithium solution; and
(B) a step of exposing a lithium solution to voltage or current to obtain lithium metal;
A method including: A method according to claim 1, wherein the lithium metal has a purity of at least 80%. A method according to claim 2, wherein the lithium metal has a purity of at least 90%. In the third method, the lithium metal has a purity of at least 95%. A method according to any one of claims 1 to 4, wherein the lithium brine contains more than 0.3 ppm of lithium. A method in claim 5, wherein the brine contains from about 50 ppm to about 75,000 ppm of lithium. A method according to claim 6, wherein the brine contains from about 100 ppm to about 40,000 ppm of lithium. A method according to any one of claims 1 to 7, wherein the solvent is immiscible with water. A method according to any one of claims 1 to 8, wherein the solvent has a greater solubility in lithium than water. A method according to any one of claims 1 to 9, wherein the solvent is an organic solvent. A method according to any one of claims 1 to 10, wherein the solvent is a polar aprotic solvent. A method in claim 11, wherein the solvent is a C1-C6 dialkyl carbonate. A method according to claim 12, wherein the solvent is diethyl carbonate. A method according to any one of claims 1 to 13, further comprising a second solvent. A method according to any one of claims 1 to 14, further comprising extracting a lithium solution with a second solvent to obtain a purified lithium solution. A method according to claim 15, further comprising exposing a purified lithium solution to voltage or current instead of a lithium solution. A method according to any one of claims 14 to 17, wherein the second solvent has increased stability at said voltage than the solvent. A method according to any one of claims 1 to 17, comprising applying voltage or current using at least two electrodes. A method comprising using three electrodes in claim 18. A method according to claim 18 or 19, comprising using a working electrode, a counter electrode and a reference electrode. A method according to any one of claims 1 to 20, comprising applying a voltage of about -6 V to about 6 V. A method in claim 21, wherein the voltage is about -5 V to about 5 V. A method in claim 22, wherein the voltage is about -4 V to about 4 V. A method according to any one of claims 1 to 23, which is performed continuously. A method according to any one of claims 1 to 24, further comprising returning the lithium solution to the extraction step after the lithium solution has been exposed to the voltage or current. A method according to any one of claims 1 to 25, further comprising exposing a lithium-containing solution or a lithium brine with or without other available impurity ions to the lithium selective membrane. A method according to claim 26, wherein a lithium-containing solution or lithium brine with or without other available impurity ions is exposed to a lithium-selective membrane while a voltage is applied. A method according to claim 26, wherein a lithium-containing solution or lithium brine with or without other available impurity ions is exposed to the lithium-selective membrane before the voltage is applied. A method according to any one of claims 1 to 28, wherein lithium is deposited on a cathode. A method according to claim 29, wherein lithium is deposited on a metal cathode. A method in claim 30, wherein lithium is deposited on a copper cathode. A method according to any one of claims 1 to 31, wherein lithium is deposited by a roll-to-roll method. A device for obtaining lithium metal,
(A) extraction chamber,
(B) Plating chamber
Including,
Here, the extraction chamber is in fluid communication with the plating chamber;
Here, the plating chamber contains a cathode and the extraction chamber contains an anode.
device. A device further comprising a lithium selective membrane in claim 33. A device according to claim 33 or 34, wherein a lithium selective membrane is located between the extraction chamber and the plating chamber. A device according to any one of claims 33 to 35, further comprising a power source connected to the anode and the cathode and capable of transmitting voltage or current. A device according to any one of claims 33 to 36, wherein the plating chamber further comprises a second reference electrode. A device according to any one of claims 33 to 37, wherein the cathode is configured to allow roll-to-roll deposition. A device according to any one of claims 33 to 38, wherein the extraction chamber is configured to allow mixing of liquids within the chamber. A device according to any one of claims 33 to 39, wherein the extraction chamber is configured to allow only a portion of the liquid from the chamber to flow into the plating chamber. A device according to any one of claims 33 to 40, wherein the extraction chamber is configured to allow only a portion of the liquid from the chamber to flow into the plating chamber after passing through the desiccant chamber. A system for cathode electrodeposition on a metal foil moving lithium (Li),
(A) a containment cell containing at least a lithium-containing solution;
(B) an extended counter electrode within the containment cell; and
(C) Extended working electrode within the containment cell
Including,
wherein the working electrode comprises a metal foil configured to move continuously through a lithium-containing solution via a roll-to-roll transport system, and the counter electrode and the working electrode are configured to be charged in a manner that drives the electrodeposition of lithium onto the extended metal foil through the lithium-containing solution.
System. A system in claim 42, further comprising a cation exchange membrane held in the storage cell and positioned between the counter electrode and the working electrode, wherein the cation exchange membrane and the storage cell together define a first chamber and a second chamber, the first chamber being configured to hold the working electrode and containing a lithium-containing organic solution, and the second chamber being configured to hold the counter electrode and containing a lithium-containing aqueous solution. A system in claim 43, wherein the cation exchange membrane defines a first cation exchange membrane, the system further comprises a second cation exchange membrane within the containment cell, the first and second cation exchange membranes define a sandwiched liquid membrane therebetween, and the sandwiched liquid membrane comprises a lithium solvent therein. A system in accordance with claim 42, further comprising a series of intermediate transport rolls holding the metal foil, the intermediate transport rolls being configured to facilitate the definition of a plurality of foil sections, a given foil section being defined between an adjacent pair of intermediate transport rolls, the counter electrode being in the form of an anode, the anode defining a plurality of anode extensions, at least one anode extension being configured to extend between an associated pair of adjacent foil sections. A system for cathode electrodeposition of lithium (Li) on a metal foil,
(A) Containment cell;
(B) an extended counter electrode within the containment cell; and
(C) A working electrode extended within a containment cell, the working electrode comprising a metal foil.
Including,
wherein a cation exchange membrane is held in a storage cell and positioned between a counter electrode and a working electrode, the cation exchange membrane and the storage cell together define a first chamber and a second chamber, the first chamber being configured to hold the working electrode and containing a lithium-containing organic solution, the second chamber being configured to hold the counter electrode and containing at least one of a lithium-containing aqueous solution or a lithium-containing saline solution, and the counter electrode and the working electrode being configured to be charged in a manner that drives both the movement of lithium ions through the cation exchange membrane and the electrodeposition of lithium onto a metal foil in contact with the lithium-containing organic solution.
System.

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