METHODS FOR LITHIUM METAL PRODUCTION DIRECT FROM LITIUM BRINE SOLUTIONS

Abstract

Method(s) and apparatus for direct lithium extraction from brine solutions via a combined solvent extraction and electrowinning process. This process involves solvent extraction integrated with an electrodeposition of lithium metal from nonaqueous solutions to with the added feature of solvent regeneration. The direct lithium metal harvest from brines via a compatible solvent will reduce significantly operational and capital costs related to the current molten salt electrolysis methods for lithium metal production.

Description

BACKGROUND

1. Technical Field

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

2. Description of Related Art

Lithium metal and many of its alloys are currently produced via a molten salt electrolysis. This molten salt electrolysis process is performed with 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 that of pure LiCl, which is >600° C. This electrolytic process yields molten lithium metal at the cathode of greater than 97% purity owing to the lower decomposition voltage of LiCl compared to KCl. Although this process yields lithium metal of high purity, its operating temperature of above 400° C. makes the process energy intensive, and the chlorine gas (Cl₂) generated at the anode is an undesirable byproduct owing to its high toxicity. Therefore, there remains a need to develop new methods of preparing high purity lithium metal.

SUMMARY

The present disclosure discloses methods and apparatuses for direct lithium plating from aqueous brine solutions, which can have lithium concentrations ranging from 100 ppm to 20,000 ppm at normal ambient temperatures via a solvent extraction-electrowinning process. This process involves lithium selective solvent extraction using a solvent immiscible with water and electrowinning lithium from the lithium impregnated solvent before it is recycled for additional lithium extraction. This process is unique due to the fact that electrowinning of lithium metal in the water immiscible solvent is utilized instead of stripping of lithium-ions back into an aqueous phase. It should be noted that, unlike base metals, electrowinning of lithium from the aqueous phase is not possible due to the high reactivity of lithium metal with water. This approach also simplifies the solvent extraction process as half of the process which involves stripping is no longer necessary as the stripping duty is carried out by electrowinning. Another advantage of this process is that it does not require fresh water, which is important in remote and extremely arid locations where lithium is mined-such as desert environments and those in South American's “lithium triangle” (Argentina, Bolivia, and Chile). Direct lithium metal electroplating or electrowinning from brines via a lithium salt compatible solvent will significantly reduce operational and capital costs related to the current methods for lithium metal production and greatly simplify the process. Electrowinning can also be used for selective extraction of a metal from a multi-component solution of a suitable solvent. Lithium metal deposited on the working electrode substrate in this process can be further purified for use in lithium metal electrode fabrication for primary or secondary lithium metal batteries. This process requires less energy and cost intensive than the current state of the art methods for commercial lithium metal production that requires a molten salt electrolysis process followed by lithium metal ingot casting and extrusion.

In one embodiment, this disclosure discloses a process that requires that the brine be combined with an additional water immiscible solvent with a greater affinity towards lithium salts in solution compared to the predominant salt impurities such as sodium, potassium, magnesium and calcium chloride as well as boric acid. In addition, the solvent benefits from having a wide electrochemical stability window. The added solvent must have a high solubility of lithium salts, such as LiCl, be immiscible with the brine solution, and have a wide electrochemical stability window. The brine solution and the additional solvent are mixed to allow for the transfer of lithium salts from the brine to the added solvent. The mixture is then left to separate where the added solvent, now saturated with lithium salt, and lithium salt depleted immiscible aqueous brine separate. The lithium salt loaded solvent is continuously overflowed or underflowed into an electrochemical cell to electroplate lithium metal onto a cathode substrate. The now lithium depleted water immiscible solvent phase is recycled and contacted with fresh incoming lithium salt containing brine for continuous extraction.

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

In another embodiment, the present disclosure provides a process in which 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 electronically conductive substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features, advantages and objects of the disclosure, as well as others which may become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only example embodiments of the invention and is therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.

FIG. 1 shows schematic illustration of one embodiment of the methods disclosed to directly obtain lithium metal from lithium brine solution through a combined solvent extraction and electrowinning approach.

FIG. 2 depicts a schematic of an electrochemical cell that is used for the electrowinning process to plate lithium metal directly onto a cathode substrate from a solution consisting of a lithium salt in a solvent.

FIG. 3 depicts an optical photograph of a prototype 3-electrode cell schematized in FIG. 2.

FIG. 4 shows an optical photograph of the interior of the 3-electrode cell shown in FIG. 3.

FIG. 5 shows an optical photograph of the full prototype setup for proof of concept. The setup consists of a 3-electrode cell connected to a potentiostat to control the electrochemical parameters during the lithium electrowinning process.

FIG. 6. shows a voltammogram (or Current-Voltage curve) obtained during the electrodeposition of lithium metal onto a copper cathode in an electrochemical cell that contains 1M LiPF₆-DEC solution as the electrolyte. Here DEC is the solvent that dissolves the LiPF₆ lithium salt with low water miscibility (<4 wt %).

FIG. 7 shows a voltammogram of lithium metal electrodeposition at a fixed voltage and the resulting lithium metal deposited onto a copper plated platinum cathode in the electrochemical cell.

FIG. 8 depicts the electrochemical cell of FIG. 3 after lithium the electrodeposition of lithium metal onto a copper substrate.

FIG. 9 shows a voltammogram (current versus voltage curve) obtained during the electrodeposition of lithium onto a copper substrate. The lithium salt used during this measurement was LiPF₆, the solvent was diethylene carbonate. The concentrate of the salt in the solvent was 1 M LiPF₆ in DEC. This salt in solvent solution was used for demonstrative purposes.

FIG. 10 shows a current versus time plot for another run of lithium deposition from solution where a constant potential of 4 V versus an Ag/AgCl reference electrode was applied. This voltage was chosen after observation of the plating voltage observed in the voltammogram of FIG. 9.

FIG. 11 shows an optical photograph of the results of the electrodeposition experiment performed to obtain the current versus time plot of FIG. 10. The left strip shows the copper cathode substrate prior to the experiment. The right strip shows lithium metal deposited onto the copper cathode substrate after the electrodeposition process was performed.

FIG. 12 shows a schematic of one of the embodiments to enable direct lithium metal deposition from brine with the assistance of a cation exchange membrane that allows for only lithium-ions to pass from the lithium brine phase to the lithium salt in solvent phase for electrodeposition onto a cathode substrate.

FIG. 13 shows a cyclic voltammogram for a lithium metal plating experiment performed in a prototype cell that was schematized in FIG. 12.

FIG. 14 shows process for simultaneous lithium extraction and electroplating.

FIGS. 15A & 15B shows a demonstration apparatus for the preparation of simultaneous lithium extraction and electroplating including the cell layout.

FIG. 16 shows the cell process including a sandwiched liquid membrane.

FIG. 17 shows a schematic of a processing cell for sustained continuous R2R production of lithium from aqueous brines.

FIG. 18 shows a schematic of a processing cell for deposition of lithium metal film onto a moving Cu foil from an organic solution medium.

FIG. 19 shows the design architecture of an electroplating cell.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The methods and systems of the present disclosure can now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The methods and systems of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure can be thorough and complete, and can fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout.

Direct lithium extractions (DLE) from brines are a challenging problem. The most abundant lithium brine resources on earth, such as those in the South American “Lithium Triangle” (Argentina-Bolivia-Chile), are concentrated brines with a high level of total dissolved solids. These lithium brines are near-saturated mixed salt solutions containing salts of cations (primarily Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, B⁺ and H⁺) and anions (primarily Cl⁺, SO₄²⁻, and OH⁻). Most direct lithium extraction technologies use fresh water to either elute the lithium from the adsorbent or strip it from a lithium selective solvent. However, areas where direct lithium extraction would be practiced are extremely arid, thus making their application more challenging.

There is a high projected demand for lithium metal as future high-capacity batteries are poised to use a lithium metal anode. Current worldwide production of lithium metal is very small, and a large demand-supply gap is projected. This disclosure presents a new, significantly lower cost approach to lithium metal production that uses no fresh water. This is accomplished by an integrated Solvent Extraction (SE) with a new Electrodeposition (ED) approach as shown in FIG. 1.

In the disclosed method of lithium metal production directly from lithium brine, lithium-ions in the brines are selectively extracted into an added solvent medium by solvent extraction or membrane-assisted solvent extraction. The lithium-ions are then electrochemically deposited onto an electronically conductive substrate from the final lithium impregnated organic or inorganic solvent medium in a process known as electrowinning. This process can also be performed with a series of solvent extraction steps prior to electrowinning lithium metal out of an organic or inorganic solvent medium onto an electronically conductive substrate. Lithium salts that can be used to electrodeposit lithium include, but are not limited to LiCl, LiClO₄, Li₂SO₄, or LiPF₆. The final purity of the deposited lithium from the full 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 in thickness from 1 nm to 5 mm. A solvent must have several key features to enable integration in the disclosed process: (1) the solvent can highly solubilize or selectively extract dissolved Li-ions/salts from aqueous brines; (2) the solvent allows the cathodic deposition of Li metal; (3) the solvent has long-term stability to resist anodic reactive degradation in the electrochemical cell during processing; and (4) the solvent must be immiscible with water. In the case of membrane-assisted solvent extraction, a membrane will provide the selective permeation of lithium from brines to an added solvent.

The lithium metal product obtained from the above process can be further purified to serve as an anode material in a primary or secondary battery in which metallic lithium serves as at least one of the electrodes. Such battery chemistries that this process might produce viable metallic lithium metal electrodes for including, but not limited to Lithium-Oxygen batteries, Lithium-sulfur batteries, rechargeable lithium metal batteries with a lithium-ion intercalating cathode, Lithium-MnO₂ primary batteries, and solid-state lithium metal batteries that contain a solid-state lithium-ion conductor as the electrolyte as opposed to a liquid electrolyte with a solvated lithium-ion conducting salt.

Battery-grade lithium metal requires additional purification after the lithium metal ingot is produced from molten salt electrolysis to obtain lithium metal that is >99.8% purity needed for secondary battery operation and an additional step for electrode fabrication for lithium metal to be used in a secondary battery. The disclosed technology can bypass the purification step and the electrode fabrication step to directly produce battery-grade lithium metal in an electrode form. Lithium metal electrodes fabricated with the disclosed method can be between 1 nm and 5 mm. This process can be performed roll-to-roll to produce a full commercial scale roll of lithium metal plated on copper electrode for use in commercial fabrication of lithium metal secondary batteries, limiting the number of process steps and further reducing the cost of production for lithium metal electrodes for relevant battery chemistries.

A. Devices for Practicing the Separations

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

In relation to FIG. 14, FIGS. 15A and 15B shows a batch-cell system 120 for use in relation to one embodiment illustrated in FIG. 14. FIG. 15A is a photographic representation of a laboratory-demonstrated version of the process cell (e.g., batch cell) system 120 and related solvo-electro-deposition process 100 for simultaneously extracting and electrodepositing lithium, in relation to an embodiment associated with FIG. 14. FIG. 15B is a graphic representation of the batch-cell system otherwise shown in FIG. 15A. The batch-cell system 120 can include a cell containment unit 122 (e.g., a vessel capable of containing liquid electrolytes and carrying, e.g., electrodes and/or a membrane), 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, for example, of a mixed metal oxide (MMO) or platinum (Pt)), a reference electrode 128 (e.g., to aid measurement of a baseline conductivity), and a metal foil 130 (e.g., made of copper). Upon electrodeposition, the resulting composite metal foil 130A can include the base metal foil 130 and a lithium layer 132. As further seen from FIG. 15B, the process cell (e.g., batch cell) system 120 can further include a membrane 134 (for example, a CEM or a selective cation exchange membrane (sCEM)); and an anodic chamber 136 carrying a Li⁺-containing aqueous brine (e.g., from reservoir tanks/containers, lakes, ponds, and/or wells) and a cathodic chamber 138 carrying a Li—X (salt) solvent organic solution medium. In an embodiment, the respective boundaries of the anodic chamber 136 and the cathodic chamber 138 can be defined, at least in part, by the cell containment unit 122 and the membrane 134. In an 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 such a manner as to drive electrodeposition of lithium onto the metal foil 330/330A extending through/into the lithium-containing organic solution (e.g., in the cathodic chamber 138). In an embodiment, the process cell 120 can define a galvanic cell. In an embodiment, the counter electrode 126 can contact the Li⁺-containing aqueous brine in the anodic chamber 136, and the working electrode 124 can contact the lithium-carrying organic solution in the cathodic chamber 138. In an embodiment, the cell containment unit 122 can be defined as a housing and/or a container.

FIG. 15B illustrates a laboratory demonstration example of the batch cell process of FIG. 14 that can enable the electrodeposition of a Li metal layer 132 (from an organic solvent Li—X solutions) onto a plate or foil cathode 130 (e.g., copper), while the organic solutions medium (e.g., lithium-containing organic electrolyte solution) of the cathodic chamber 138 can simultaneously extract lithium from an aqueous solution or brine of the anodic chamber 136. An Li+-conducting or Li+-selective membrane 134 can be placed in the middle between the organic and aqueous solutions (as seen in FIG. 15B). This extraction-electrodeposition cell 120 can be configured with two chambers 136, 138 defined by the cell containment unit 122 and the intermediary membrane 134. One chamber 136 can contain the aqueous brine solution(s), and the other 138 can contain the organic solutions. Also, the respective solutions can be respectively replenished from an outside reservoir tank and/or natural source (e.g., lakes, ponds, aquifers, and/or wells), as needed, with the lake 102 shown in FIG. 14 being one such an example of a replenishment source. The process 100 of FIGS. 15A & 15B can be considered to be a solvo-electro extraction-electrodeposition process in a single-unit process cell 120. Depending on the cell dimensions, configurations, and the solutions of choices (brine and organic), the current density for the two-electrode electrodeposition can be in the range of 0.1-100 mA per cm² of membrane or cathodic surface area. During a fixed current electrodeposition, the operating voltage can go from 0 to 10 volts (which include the Li reduction potential of ˜3.2V relative to the Ag/AgCl (KCl) reference electrode plus the IR drops).

FIG. 16 illustrates a derivate cell configuration, in accordance with an embodiment of the present disclosure. The derivative cell configuration, generally labelled as process 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, for example, of a 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., including a pair of CEM's and an intermediate solvent zone (not individually labelled)), an anodic chamber 236 carrying a Lit-containing aqueous brine, and a cathodic chamber 238 carrying Li—X solvent organic solution medium. Throughout this disclosure, it is to be understood that components that are similarly numbered (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 to the contrary with respect to a given embodiment.

In comparing FIG. 15B and FIG. 16, the middle membrane 134 (CEM or selective CEM) in 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 include a Li—X solvent sandwiched with two solid Li-conducting membranes or CEMs (components not individually labelled). The liquid membrane 234 can provide the Li⁺ selectivity for permeating from the aqueous solutions of the anodic chamber 236 to the organic solutions of the cathodic chamber 238. As such, FIG. 16 illustrates a process cell 220 for a solvo-electro extraction-electrodeposition process in a single-unit batch that utilizes a sandwiched liquid membrane 234 to enable selective transport of Li ions from the aqueous brine of the anodic chamber 236 into the organic solution medium of the cathodic chamber 238. In the case of recirculation of the liquid membrane 234 of the liquid in the middle chamber through an external loop of dewatering column, the liquid membrane (or chamber) can serve as a barrier to block the transport water molecules (while allowing Li transfer) from the aqueous brine chamber to the organic solution chamber. This would help sustained hours of operation in simultaneous extraction and deposition.

FIG. 17 illustrate an embodiment of a process cell 320 conducive to industrial large-scale continuous production of Li metal film deposit on a substrate foil (e.g., a copper foil or other metal film or web) while extracting lithium from an aqueous brine, for example, using a roll-to-roll (R2R) arrangement. The process cell 320, as illustrated in FIG. 17, can include a cell containment unit 322 (e.g., a vessel capable of containing liquid electrolytes and carrying, e.g., electrodes and/or a membrane), 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, for example, of a mixed metal oxide (MMO) or platinum (Pt)), a reference electrode 328 (e.g., usually positioned close (within a few millimeters) to the cathode surface), a metal foil 330 (e.g., copper foil), a composite metal foil 330A (e.g., made of copper upon coating with a lithium layer), a membrane 334 (e.g., a CEM or sCEM), an anodic chamber 336 carrying a Li⁺-containing aqueous brine, a brine source 336A (e.g., lake, well, aquifer, and/or storage container) for use in the anodic chamber 336, a cathodic chamber 338 carrying a Li—X solvent organic solution medium, an input/feed foil roll 340A, a product foil roll 340B (e.g., lithium-coated copper foil), an inert gas (e.g., argon (Ar)) gas-filled holding tank 342 (e.g., in which the product foil roll 340B can be retained), and a dewatering column 344 (e.g., a zeolite dewatering column bed). In an embodiment, the membrane 334 can be positioned between the working electrode 324 and the counter electrode 326. The counter electrode 326 and the working electrode 324 can be configured to be charged in such a manner as to drive electrodeposition of lithium onto the metal foil 330/330A extending through the lithium-containing organic solution. The process cell 320 can further include connective conduits and/or one or more additional intermediate rollers (such as shown but not labeled), as needed, to facilitate fluid movement/replenishment and/or foil movement.

The roll-to-roll process cell 320 of FIG. 17 can facilitate a continuous, multiple-step deposition process. In a first step, an aqueous brine solution in the anodic chamber 336 can be replenished as necessary to continuously provide Li⁺ from an outside source or reservoir 336A. In a second step, Li⁺ can be continuously transferred from aqueous phase into organic phase, via the membrane 334. In a third step, electrodeposition of Li metal onto the moving copper cathode 324 (e.g., in the form of a copper foil 330 supplied from the feed foil roll 340A) can occur in the cathodic (e.g., organic solution) chamber 338, while the Cu foil web 330, 330A can continuously move through the electrodeposition zone. The water content level of the organic phase can be controlled by a dewatering column 344 and the related recirculation loop. Per a fourth step, the product roll 340B of a 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 suitably inert gas therein along with any hardware needed to facilitate the collection of the product roll 340B.

FIG. 18 illustrates a roll-to-roll (R2R) cathodic deposition process for depositing a lithium (Li) metal film onto a moving metal (e.g., copper) foil web via an organic solution, in accordance with an embodiment of the present disclosure. The R2R cathodic deposition process can be achieved using a roll-to-roll (R2R) process cell 420. The R2R process 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, for example, of a 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 upon coating with a lithium layer), a cathodic chamber 438 carrying a Li—X solvent organic solution medium, an input/feed foil roll 440A, a product foil roll 440B (e.g., lithium-coated copper foil), an argon (Ar) gas-filled holding tank 442 (e.g., in which product foil roll 440B can be retained), and a dewatering 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 manner as to drive electrodeposition of lithium onto the metal foil 430/430A extending through the lithium-containing organic solution. Note, unlike the system 320 shown in FIG. 17, the R2R process cell 420 may, for example, not incorporate a separate anodic chamber and/or a membrane, as an organic Li-carrying solution serves as the Li source, instead of a brine. Instead, both the anode 426 and the cathode 428 can be included in the same chamber (e.g., 438), thereby simplifying the construction relative to the system 320 of FIG. 16.

Furthermore, with respect to FIG. 18, the R2R cathodic deposition process using a roll-to-roll (R2R) process cell 420 can be employed if one or more lithium-containing organic solutions serve as the Li source, thereby permitting the R2R arrangement to be simplified, as discussed above. In this case, the water content of the organic solutions for the electrodeposition zone (e.g., 438) for the moving cathode 424 (e.g., metal (e.g., Cu) foil web 430; and the composite (e.g., Li—Cu) foil web 430A) can be controlled to minimize the dissolution rate of deposited Li metal (not individually labelled). Also, more Li-containing organic solutions can be continuously supplied into the electrodeposition tank/chamber 438 during the continuous, sustained production. To minimize the anodic degradation for a longer lifetime of organic medium, the fixed anode 426 can be placed outside the organic solution and/or the anode 426 can be modified with one or more coating materials (such as LFP (lithium iron phosphate)). Also, other additives (such as ionic liquids) can be added or otherwise utilized in the organic phase to enhance the Li—X salt solubility and refine electrodeposition performances. For example, an ionic liquid (organic phase) can be heated to a little above 180° C. (i.e., the Li metal melting point) to enable liquid Li metal electrodeposition and harvest around the cathode.

In an embodiment, the linear speed (v) of the copper web driven, the electrical deposition current (i) applied, the width (w) the lithium layer deposited, and the current efficiency (η) of the lithium deposition can be correlated by:

$\begin{array}{cc}Q=i\eta /\mathrm{vw}& \mathrm{Equation}1\end{array}$

where Q is the total charge passed therethrough. Q is related to the quantity of lithium metal deposited on the cathode surface. For example, for lithium with a single positive charge, each charge corresponds to a single lithium atom.

The electrodeposition time can be defined by the following equation:

$\begin{array}{cc}t=\eta /\mathrm{vw}& \mathrm{Equation}2\end{array}$

In order to deposit a useful lithium metal for battery anode, it can be important to control the plating current density and the thickness. In an embodiment, the lithium deposition rate can be controlled at a current density ranged from 0.2 mA/cm² to 0.8 mA/cm² and a thickness range equivalent of 1 mAh/cm² to 100 mAh/cm², where mA=milliamps; cm=centimeters; and h=hours. Per above, the thickness range equivalent can be considered to be proportional to the thickness produced, given that each charge corresponds to a single lithium atom. Using the two ranges, the electrodeposition time can be calculated using Equations 1 & 2. For example, if an equivalent total of 100 mAh/cm² of Li is to be plated while doing so at a rate of 0.2 mA/cm², the total deposition time converts to 500 hours. Based on such conditions for Li electroplating, the deposition time may range, for example, from 1.25 to 500 hours, based on the parameters chosen and the thickness/thickness equivalent desired.

In an embodiment, a design with an increase to the overlap of the cathode and anode can enable a large electroplating time while still allowing for a reasonable linear production speed. It is to be understood that various design architectures can be employed to achieve the electroplating conditions. FIG. 19 displays one such design for electroplating, with the design featuring extended overlap surface areas for the two electrodes. The R2R process cell 520 can include 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, for example, of a mixed metal oxide (MMO) or platinum (Pt)), and a metal foil 530 (e.g., copper foil), similar to R2R process cell 420. Unlike the R2R process cell 420, the R2R process cell 520 can further include a series of intermediate transport rolls 540C that carry the metal foil 530. The intermediate transport rolls 540C can be configured to facilitate the definition of a plurality of foil sections (e.g., two of which, 530A and 530B, are labeled), and a given foil section can be defined between a proximate pair of intermediate transport rolls 540C. The foil sections can together define a plurality of adjacent foil sections, for example, 530A and 530B. Additionally, a given counter electrode 526 can be considered to be an anode and may include/define a plurality of anode extensions, one of which is labeled as 526A (i.e., defining a multi-prong anode 526). Each anode extension can extend between an accompanying pair of adjacent foil sections (e.g., anode extension 526A between foil sections 530A and 530B), together defining a given electroplating zone Z, of which a plurality of such electroplating zones Z can be defined by the R2R process cell 520. The electrode surface overlap area A can facilitate an increase in the plated quantity and/or can allow for a faster linear speed v in Equation 2. In an embodiment, the R2R electroplating process facilitated by the R2R process cell 520 can enable a lithium electroplating reaction time ranging, for example, from 0.5 to 1000 hours, 5-400 hours, or 20-300 hours. In an embodiment, the large surface area overlap A associated with the R2R process cell 520 may be extended to a mass transport window, where ion transport in the electrolyte is driven by the multi-prong anode 526.

Note that the processing cell configuration is necessarily not limited to the illustrative designs shown in the above-described figures. Besides the variation in organic solution engineering, the electrode design and material type can be easily modified for better performances, and such modifications are considered to be within the scope of the present disclosure. Further, unless otherwise expressly excluded, it is to be understood that components described with respect to the various embodiments may be mixed and/or matched with respect to one another. Additionally, while copper has been discussed as a candidate material upon which to electro-deposit lithium, it is to be understood that other conductive metals or metal alloys may serve as appropriate substrates upon which to deposit the lithium.

In summary, one or more embodiments of the present disclosure can result in (1) a roll-to-roll Li metal film (battery anode) production technology; and/or a lithium-metal production and lithium-ion extraction technology from either aqueous solutions or from organic solutions. The integrated hybrid solvo-electro-processing can enable the simultaneous lithium extraction and metal production in a single-stage batch or continuous operation. The “solvo-processing” can take advantage of the organic solutions as a Lit-transporting medium suitable for electrodeposition or as a solvent(s) for selective extraction of lithium from aqueous brines. In the former case, a Li⁺-selective membrane (solid CEM or liquid) between the aqueous phase and organic phase can add Li⁺-transporting selectivity for DLE (direct lithium extraction) from the source brine. The “electro-processing” of the present disclosure can utilize the electrically enhanced rate of electrodialysis (for lithium extraction and transporting mobility) and/or electrodeposition (for Li metal film production). The Aqueous-Organic biphase electrodialysis can be uniquely implemented in extracting/transporting lithium from aqueous brines/solutions into an organic solution medium. Relative to the competing electrowinning processing for Li metal production, the present technology can provide (1) lower cost option for Li metal film production as battery anode (<20 μm thick); and/or (2) simultaneous DLE from aqueous brine and Li metal film electrodeposition in a single integrated process.

The present technology can manifest itself in one or more features. The technology can allow combined Li extraction (from aqueous brine) and Li metal (battery anode) production simultaneously in a continuous process, which needs no processing water. The process can be operated in either a roll-to-roll (R2R) or batch mode for Li metal production (via electrodeposition of Li from an organic phase) and/or continuous lithium extraction from aqueous brines. The technology can implement an organic phase as an electrodeposition medium that can be either lithium salt-soluble or lithium ion-selective (like those organic solutions obtained from solvent extraction). The system can feature a dewatering method that can control the water content of the organic phase, thus allowing sustained electrodeposition of Li metal with better current efficiency and/or better quality of Li metal fil deposit. The method associated herewith can yield a faster direct lithium extraction (DLE) rate from aqueous brines because of the larger Lit concentration gradient between an aqueous and organic phase driven by electrodeposition phenomenon. The integrated process can take advantage of an electrodialysis-like phenomenon for faster ion mobility and/or transport from an aqueous phase into an organic phase. The present system can allow for lower temperature (e.g., room temperature and/or ambient), lower cost processing than molten-salt electrowinning. A R2R version of the present system and method can be used to directly produce a thin film deposit of Li metal on copper foil web, which can be used, for example, as a suitable platform for a Li battery anode.

Below are proof-of-principle example cases that provide methods and specific conditions to enable lithium metal electrodeposition from a solvent-extracted solutions. The invention here is by no means limited to these examples.

Example 1: Lithium Deposition from an Organic Solvent with LiPF₆ as an Ionically Conducting Salt

FIG. 2 shows a schematic of the three-electrode electrochemical cell that was used for the electrodeposition of lithium metal, which consists of a Working Electrode (cathode, such as copper, copper plated platinum, or another electronically conductive substrate), a Reference Electrode (such as Ag/AgCl), and a Counter Electrode (Anode). The exact experimental cell for the demonstration of lithium metal electrowinning direct from a solvent medium with a solvated lithium salt is shown in FIG. 3.

Specifically, in one embodiment, the electrochemical cell uses a cathode copper rod as the working electrode that is electrically insulated on the side such that only the well-defined circular flat surface (0.5 cm²) at the bottom end is exposed to the electrolyte solution. A glass encapsulated reference electrode (Ag/AgCl (1M KCl)) faces (<1-mm gap) is used as the reference electrode. A platinum foil ring anode is placed concentrically at the bottom part of the electrodeposition cell to serve as the counter electrode. The above specified components are shown in FIG. 4 for clarity. Note that the electrochemical cell design and electrode choices (in shape, material type, and dimension) are not limited to this example in geometrical shape, physical dimension, or material composition. The full experimental setup for the electrochemical cell and the lithium metal electrowinning process is shown in FIG. 5.

FIG. 6 shows a voltammogram obtained during an initial linear sweep voltammetry experiment to determine the plating voltage of lithium metal onto the copper current collector in the experimental setup portrayed in FIG. 5 with the experimental cell shown in FIG. 3. The electrolyte solution for this demonstration was 1M LiPF₆ in diethyl carbonate (DEC). A reduction-oxidation (redox) reaction is observed to occur around −2.8V versus the Ag/AgCl reference electrode, which is denoted by the drastic increase in the absolute value of the measured current of the electrochemical cell. This initial onset of current increase is attributed to the breakdown of the DEC solvent, which is known to have a limited electrochemical stability window. A secondary redox reaction begins at roughly 3.2V versus Ag/AgCl which is attributed to the onset of electrochemical plating of lithium. This observed potential for lithium deposition is consistent with the thermodynamically predicted potential for this reaction according to the table of standard reduction potentials—i.e. the difference in standard reduction potentials of lithium metal and the Ag/AgCl reference electrode (−3.045 V-0.2223 V=−3.2673 V). This agreement between the experimentally observed potential and the thermodynamically predicted potential is a preliminary indication that lithium metal can be electrowon from solution. For reference, the relevant standard reduction reactions and corresponding potentials relative to the standard hydrogen electrode (SHE) are provided.

Li⁺e⁻→Li−3.045 V (Cathodic reductive reaction for Li metal deposition)

AgCl+e⁻→Ag⁺+Cl⁻0.2223 V (Reference electrode, Ag/AgCI (1M KCl))

2H⁺+2e⁻→H₂ 0.00V (Standard Hydrogen Electrode, SHE)

To produce a meaningful amount of metallic lithium, a chronoamperometric experiment was performed in which the voltage of the electrochemical cell was held constant, and the current was recorded as a function of time. The results from this experiment are presented in FIG. 7. During this measurement, the voltage of the cell was held constant at −3.5V versus the Ag/AgCl reference electrode. An optical photograph of the electrochemical cell is shown in FIG. 8 in which a large grey solid deposit has formed on the copper working electrode. For analysis, the grey deposit was harvested and washed with a N-methyl pyrrolidine (NMP). A quick test to determine if the grey deposit contains metallic lithium is to submerge the solid in water. Metallic lithium violently reacts with water through the reaction Li(s)+H₂O (I)→LiOH (I)+H₂ (g). When the solid deposited harvested from chronoamperometric experiment was submerged into deionized water, gas bubbles immediately formed, which can be attributed to hydrogen gas evolution. Additionally, the grey solid gradually dissolved away to expose the underlying copper substrate. The submerged water 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 between 2-7 micron layers of lithium were deposited in different experiments. The current efficiencies were calculated to be in the 60-80% range.

In the later stage of the electrodeposition, dendritic lithium metal forms (FIG. 5). The Faradaic Efficiency for this lithium metal electrodeposition process is calculated determined to be 61%. In principle, the lithium metal deposition rate (mg/s) onto the cathode surface can be controlled by varying the applied voltage and current in the electrochemical cell. Faraday's law in one form is:

$m/MW=\left[\mathrm{It}\right]/\left[nF\right]$

Where m=mass of deposited species (g), MW=molecular weight of the deposited species, I=current (A), 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 of the equation are either experimentally measured, experimentally applied, or physical constants.

The equation can be rewritten to determine the rate of lithium plating or lithium deposition:

$m/t=\left[\mathrm{IM}W\right]/\left[nF\right]$

If I is unknown but m/t is known then equation can be rewritten once more to solve for the required current to be applied to obtain a desired deposition rate:

$I=\left[m/\mathrm{tnF}\right]/MW$

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

Example 2: Scalability Demonstration for Electrowinning of Lithium Metal for Commercial Lithium Metal Electrode Production

The copper rod cathode surface in the previous example had a limited surface area for lithium deposition (0.5 cm²). To enlarge the surface for cathodic electrodeposition of Li metal, a long strip of copper was used as the working electrode as opposed to a single end-face of a copper rod. This copper strip had an electrochemically active surface area that was over 10 times greater than the face of the copper rod that was used in the original lithium electrowinning experiments. This enlargement of the working electrode demonstrates the scalability of this approach towards commercial applications, which require lithium to be deposited on a copper substrate up to three meters wide on a roll-to-roll basis.

Similar proof-of-concept experiments as with the previous example were performed for this larger copper substrate working electrode. A linear sweep voltammogram is presented in FIG. 9 that shows a similar onset potential for the deposition of lithium metal as the smaller electrowinning experiment. FIG. 10 shows a current versus time plot for a chronoamperometric experiment performed with the larger copper working electrode in the electrowinning cell. The cell voltage was held at −4V versus the Ag/AgCl reference electrode for this measurement. The voltage for this example was greater than that of Example 1 to overcome any kinetic barriers that may arise because of the larger electrochemically active surface area of the cathode in this instance. As with Example 1, the electrochemical cell for electrowinning lithium metal from a solvent medium consisted of an Ag/AgCl reference electrode, a platinum counter electrode and 1M LiPF₆ in DEC as the electrolyte. Visual confirmation of lithium metal deposition onto the larger copper working electrode is provided in FIG. 11 where the copper substrate is shown before and after the electrowinning process.

The disclosed method for lithium metal production from brine may be easily modified to utilize existing commercial electroplating or electrowinning equipment or components. The electrowinning cell can take advantage of the roll-to-roll cathodic deposition for scalable, large surface area deposition of lithium metal onto a substrate surface that is submerged and pulled through the platting electrolyte medium. An example of this embodiment can include rolling copper foil through a liquid lithium electrolyte medium to plate lithium metal on the copper foil substrate. Some existing commercial electrodeposition cells, such as industrial electrowinning or electroplating cells, may 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 enclosed methods allows for the use of a cation exchange membrane to assist in the separation of lithium-ions from concentrated lithium brine into an alternative solvent media that lithium metal may then be plated from. An electrochemical cell that may be used in this process is schematized in FIG. 12. In this cell, lithium-ions are electrochemically driven from the concentrated lithium brine, through the lithium-ion selective cation exchange membrane, into a solvent medium, and then finally plated onto a metallic substrate that is used as the cathode in the cell. A cyclic voltammogram is provided in FIG. 13 for such an electrochemical cell. The electrochemical cell used for this experiment consisted of a copper substrate cathode, a platinum anode, concentrated lithium brine as the anolyte, a lithium conducting salt solvated in a solvent as the catholyte, and a cation exchange membrane as the separator between the compartments that contained the two different electrolyte media. Although this experiment indicates the reversibility of the process, in actuality the concentrated lithium brine would continuously be refreshed 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 Specification, which includes the Summary, Brief Description of the Drawings and the Detailed Description, and the appended Claims refer to particular features (including process or method steps) of the disclosure. Those of skill in the art understand that the invention includes all possible combinations and uses of particular features described in the Specification. Those of skill in the art understand that the disclosure is not limited to or by the description of embodiments given in the Specification.

Those of skill in the art also understand that the terminology used for describing particular embodiments does not limit the scope or breadth of the disclosure. In interpreting the Specification and 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 appended Claims have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs unless defined otherwise.

As used in the Specification and appended Claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly indicates otherwise. The verb “includes” and its conjugated forms should be interpreted as referring to elements, components or steps in a non-exclusive manner. The referenced elements, components or steps may be present, utilized or combined with other elements, components or steps not expressly referenced. The verb “operatively connecting” and its conjugated forms means to complete any type of required junction, including electrical, mechanical or fluid, to form a connection between two or more previously non-joined objects. If a first component is operatively connected to a second component, the connection can occur either directly or through a common connector. “Optionally” and its various forms means 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 occur.

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

The systems and methods described herein, therefore, are well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While example embodiments of the system and method have been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications may readily suggest themselves to those skilled in the art and are intended to be encompassed within the spirit of the system and method disclosed herein and the scope of the appended claims.

Claims

1. A method of preparing lithium metal comprising: (A) extracting lithium brine with a solvent to obtain a lithium solution; and(B) exposing the lithium solution to a voltage or current to obtain lithium metal.

2. The method of claim 1, wherein the lithium metal comprises a purity of at least 80%.

3. The method of claim 2, wherein the lithium metal comprises a purity of at least 90%.

4. The method of claim 3, wherein the lithium metal comprises a purity of at least 95%.

5. The method according to any one of claims 1-4, wherein the lithium brine comprises greater than 0.3 ppm of lithium.

6. The method of claim 5, wherein the brine comprises from about 50 ppm to about 75,000 ppm of lithium.

7. The method of claim 6, wherein the brine comprises from about 100 ppm to about 40,000 ppm of lithium.

8. The method according to any one of claims 1-7, wherein the solvent is immiscible with water.

9. The method according to any one of claims 1-8, wherein the solvent has a greater solubility for lithium than water.

10. The method according to any one of claims 1-9, wherein the solvent is an organic solvent.

11. The method according to any one of claims 1-10, wherein the solvent is a polar aprotic solvent.

12. The method of claim 11, wherein the solvent is a C1-C6 dialkyl carbonate.

13. The method of claim 12, wherein the solvent is diethyl carbonate.

14. The method according to any one of claims 1-13, wherein the method further comprises a second solvent.

15. The method according to any one of claims 1-14, wherein the method further comprises extracting the lithium solution with the second solvent to obtain a purified lithium solution.

16. The method of claim 15, wherein the method further comprises exposing the purified lithium solution to a voltage or current instead of the lithium solution.

17. The method according to any one of claims 14-17, wherein the second solvent has increased stability at the voltage than the solvent.

18. The method according to any one of claims 1-17, wherein the method comprises using at least two electrodes to apply the voltage or current.

19. The method of claim 18, wherein the method comprises using three electrodes.

20. The method of either claim 18 or claim 19, wherein the method comprises using a working electrode, a counter electrode, and a reference electrode.

21. The method according to any one of claims 1-20, wherein the method comprises applying a voltage from about −6 V to about 6 V.

22. The method of claim 21, wherein the voltage is from about −5 V to about 5 V.

23. The method of claim 22, wherein the voltage is from about −4 V to about 4 V.

24. The method according to any one of claims 1-23, wherein the method is performed continuously.

25. The method according to any one of claims 1-24, wherein the method further comprises returning the lithium solution after the lithium solution has been exposed to the voltage or current to the extraction step.

26. The method according to anyone of claims 1-25, wherein the method further comprises exposing the lithium containing solution or lithium brine with or without other soluble impurity ions to a lithium selective membrane.

27. The method of claim 26, wherein the lithium containing solution or lithium brine with or without other soluble impurity ions is exposed to the lithium selective membrane while the voltage is applied.

28. The method of claim 26, wherein the lithium containing solution or lithium brine with or without other soluble impurity ions is exposed to the lithium selective membrane before the voltage is applied.

29. The method according to any one of claims 1-28, wherein the lithium is deposited on the cathode.

30. The method of claim 29, wherein the lithium is deposited on a metal cathode.

31. The method of claim 30, wherein the lithium is deposited on a copper cathode.

32. The method according to any one of claims 1-31, wherein the lithium is deposited in a roll-to-roll method.

33. An apparatus for obtaining lithium metal comprising: (A) an extraction chamber;(B) a plating chamber;wherein the extraction chamber is in fluid communication with the plating chamber;wherein the plating chamber comprises a cathode and the extraction chamber comprises an anode.

34. The apparatus of claim 33, wherein the apparatus further comprises a lithium selective membrane.

35. The apparatus of either claim 33 or claim 34, wherein the lithium selective membrane is positioned between the extraction chamber and the plating chamber.

36. The apparatus according to any one of claims 33-35, wherein the apparatus further comprises a power source connected to the anode and cathode and capable of delivering a voltage or current.

37. The apparatus according to any one of claims 33-36, wherein the plating chamber further comprises a second reference electrode.

38. The apparatus according to any one of claims 33-37, wherein the cathode is configured to allow roll-to-roll deposition.

39. The apparatus according to any one of claims 33-38, wherein the extraction chamber is configured to allow mixing of liquid inside the chamber.

40. The apparatus according to any one of claims 33-39, wherein the extraction chamber is configured to allow only part of the liquid from the chamber to flow into the plating chamber.

41. The apparatus according to any one of claims 33-40, wherein the extraction chamber is configured to allow only part of the liquid from the chamber to flow into the plating chamber after passing through a desiccant chamber.

42. A system for cathodic electrodeposition of lithium (Li) onto a moving metal foil, the system comprising: (A) a containment cell carrying at least a lithium-containing solution;(B) a counter electrode extending in the containment cell; and(C) a working electrode extending in the containment cell,wherein the working electrode comprising a metal foil configured to be continuously moved through the lithium-containing solution via a roll-to-roll conveyance system, the counter electrode and the working electrode configured to be charged in such a manner as to drive electrodeposition of lithium onto the metal foil extending through the lithium-containing solution.

43. The system of claim 42, further comprising a cation exchange membrane carried in the containment cell and positioned between the counter electrode and the working electrode, the cation exchange membrane and the containment cell together defining a first chamber and a second chamber, the first chamber carrying the working electrode and configured to contain the lithium-containing organic solution, the second chamber carrying the counter electrode and configured to contain a lithium-containing aqueous solution.

44. The system of claim 43, wherein the cation exchange membrane defining a first cation exchange membrane, the system further comprising a second cation exchange membrane in the containment cell, the first and second cation exchange membranes defining a sandwiched liquid membrane therebetween, the sandwiched liquid membrane including a lithium solvent therein.

45. The system of claim 42, further comprising: a series of intermediate transport rolls for carrying the metal foil, the intermediate transport rolls configured to facilitate the definition of a plurality of foil sections, a given foil section being defined between a proximate pair of intermediate transport rolls, the counter electrode being the form of an anode, the anode defining a plurality of anode extensions, at least one anode extension configured to extend between an accompanying pair of adjacent foil sections.

46. A system for cathodic electrodeposition of lithium (Li) onto a metal foil, the system comprising: (A) a containment cell;(B) a counter electrode extending in the containment cell;(C) a working electrode extending in the containment cell, the working electrode comprising a metal foil; andwherein a cation exchange membrane carried in the containment cell and positioned between the counter electrode and the working electrode, the cation exchange membrane and the containment cell together defining a first chamber and a second chamber, the first chamber carrying the working electrode and configured to contain a lithium-containing organic solution, the second chamber carrying the counter electrode and configured to retain at least one of a lithium-containing aqueous solution or a lithium-containing brine, the counter electrode and the working electrode configured to be charged in such a manner as to drive both lithium ion movement through the cation exchange membrane and electrodeposition of lithium onto the metal foil contacting the lithium-containing organic solution.