Patent Publication Number: US-2021189578-A1

Title: Systems and Methods for Concentrating Ions

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 62/949,763, filed on 18 Dec. 2019, the entire contents and substance of which is incorporated herein by reference in its entirety as if fully set forth below. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to systems and methods for concentrating ions. Particularly, embodiments of the present disclosure relate to electrochemical systems and methods for concentrating ions. 
     BACKGROUND 
     Lithium is a strategically important resource, and a stable lithium supply is undoubtedly a key element to a sustainable future. As civilization continues to develop, humanity continuously improves on the ability to harness energy. Civilization has progressed from animal power to steam power, and now civilization resides in the era of electrical power. However, today&#39;s electricity is largely obtained from fossil fuels that generate significant greenhouse gas emissions, creating a climate change risk. Due to the growing concern over this global challenge, it is desirable to create clean, zero-emission technologies for power generation. To achieve such a sustainable future, development in energy storage, generation, transmission, and usage will play a key role along the way. 
     In the field of energy storage devices, lithium-ion batteries (LIBs) have become a focal point and dominant market force due to their preeminent performance. Recently, the prevalence of mobile devices, electric vehicles, internet of things devices, computation devices, and similar industries have led to an unprecedented demand for LIBs. For instance, the global electric vehicle cumulative sales are expected to rise from 2 million in 2016 to 1.8 billion by 2060. Additionally, the global demand for lithium is projected to quadruple from 2010 to 2025. That is to say, lithium is one of the most important resources for developing industries in the foreseeable future. 
     However, current lithium production cannot meet the global demands of lithium. Currently, the majority of lithium production takes place in brine lakes and salt pans. Current methods, such as the lime-soda evaporation method, suffer from long manufacturing cycles and serious environmental impacts. These drawbacks lead to increased costs of energy storage and further hinder emerging technologies in energy storage. Therefore, the scarcity of lithium sources combined with inefficient methods of extracting said sources are a looming concern. 
     What is needed, therefore, are systems and methods of lithium extraction that can more efficiently extract lithium from natural sources while minimizing the environmental impacts of such extraction processes. Embodiments of the present disclosure address this need as well as other needs that will become apparent upon reading the description below in conjunction with the drawings. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     The present disclosure relates generally to systems and methods for concentrating ions. Particularly, embodiments of the present disclosure relate to electrochemical systems and methods for concentrating ions. 
     An exemplary embodiment of the present disclosure can provide a system for concentrating ions, the system comprising: an electrochemical cell comprising: a first electrode; a second electrode; a first solution in fluid communication with the first electrode and the second electrode, the first solution containing a first ion and a second ion, the second ion different from the first ion; and a molecular sieve disposed on the first electrode, the molecular sieve configured to selectively permit the first ion to pass from the solution to the first electrode. 
     In any of the embodiments disclosed herein, the molecular sieve can comprise a polymer. 
     In any of the embodiments disclosed herein, the molecular sieve can be further configured to selectively prevent the second ion from passing from the first solution to the first electrode. 
     In any of the embodiments disclosed herein, the system can further comprise a voltage source configured to apply a differential voltage between the first electrode and the second electrode. 
     In any of the embodiments disclosed herein, the differential voltage can cause the electrochemical cell to undergo a redox reaction, wherein the redox reaction causes the first ion to absorb into the first electrode. 
     In any of the embodiments disclosed herein, the system can further comprise a second solution configured to, when contacted with the first electrode, desorb the first ion from the first electrode and into second solution. 
     In any of the embodiments disclosed herein, the first ion can be a lithium ion and the first electrode is a lithium-based electrode. 
     In any of the embodiments disclosed herein, the first solution can be a brine containing the first ion. 
     Another embodiment of the present disclosure can provide a method of concentrating ions, comprising: contacting a first solution to an electrochemical cell, the first solution containing a first ion and a second ion, the second ion different than the first ion, the electrochemical cell comprising a first electrode, a second electrode, and a molecular sieve disposed on the first electrode, the molecular sieve configured to selectively permit the first ion to pass from the solution to the first electrode; applying a first differential voltage between the first electrode and the second electrode, wherein the first differential voltage causes the electrochemical cell to undergo a redox reaction such that the first ion absorb into the first electrode; contacting a second solution with the electrochemical cell; and applying a second differential voltage between the first electrode and the second electrode, wherein the second differential voltage causes the first ion to desorb from the first electrode. 
     In any of the embodiments disclosed herein, the molecular sieve can comprise a polymer. 
     In any of the embodiments disclosed herein, the molecular sieve can be further configured to selectively prevent the second ion from passing from the first solution to the first electrode. 
     In any of the embodiments disclosed herein, the first ion can be a lithium ion and the electrode is a lithium-based electrode. 
     In any of the embodiments disclosed herein, the first solution can be a brine containing the first ion. 
     Another embodiment of the present disclosure can provide an electrochemical cell for concentrating ions, the electrochemical cell comprising: a first electrode; a second electrode; a first solution in fluid communication with the first electrode and the second electrode, the first solution containing a first ion and a second ion, the second ion different than the first ion; and a molecular sieve disposed on the first electrode, the molecular sieve configured to selectively permit the first ion to pass from the solution to the first electrode. 
     In any of the embodiments disclosed herein, the molecular sieve can comprise a polymer. 
     In any of the embodiments disclosed herein, the molecular sieve can be further configured to selectively prevent the second ion from passing from the first solution to the first electrode. 
     In any of the embodiments disclosed herein, the electrode can be in electrical communication with a voltage source configured to apply a differential voltage between the first electrode and the second electrode. 
     In any of the embodiments disclosed herein, the differential voltage can cause a redox reaction, wherein the redox reaction causes the first ion to absorb into the first electrode. 
     In any of the embodiments disclosed herein, the first ion can be a lithium ion and the first electrode is a lithium-based electrode. 
     In any of the embodiments disclosed herein, the first solution can be a brine containing the first ion. 
     These and other aspects of the present disclosure are described in the Detailed Description below and the accompanying figures. Other aspects and features of embodiments of the present disclosure will become apparent to those of ordinary skill in the art upon reviewing the following description of specific, exemplary embodiments of the present invention in concert with the figures. While features of the present disclosure may be discussed relative to certain embodiments and figures, all embodiments of the present disclosure can include one or more of the features discussed herein. Further, while one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used with the various embodiments of the invention discussed herein. In similar fashion, while exemplary embodiments may be discussed below as device, system, or method embodiments, it is to be understood that such exemplary embodiments can be implemented in various devices, systems, and methods of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate multiple embodiments of the presently disclosed subject matter and serve to explain the principles of the presently disclosed subject matter. The drawings are not intended to limit the scope of the presently disclosed subject matter in any manner. 
         FIG. 1  illustrates an example system for concentrating ions in accordance with the present disclosure. 
         FIG. 2A  illustrates an example molecular sieve in an electrochemical cell in accordance with the present disclosure. 
         FIG. 2B  illustrates an exploded view of the molecular sieve depicted in  FIG. 2A  in accordance with the present disclosure. 
         FIG. 3  illustrates a flowchart of a method of concentrating ions in accordance with the present disclosure. 
         FIG. 4  is a chart of the discharge curve for an electrode in various electrolytes in accordance with the present disclosure. 
         FIG. 5A  is a chart of the simulated steric energy of lithium ions in a molecular sieve in accordance with the present disclosure. 
         FIG. 5B  is a chart of the simulated steric energy of sodium ions in a molecular sieve in accordance with the present disclosure. 
         FIG. 6  is a chart of electrochemical performance of an electrode and an electrode coated with a molecular sieve in accordance with the present disclosure. 
         FIG. 7  is a chart of the molar ratio of lithium to sodium in different recovery solutions in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     As stated above, a problem with current lithium production processes is the scarcity of lithium. Furthermore, the processes to extract such scarce lithium have long manufacturing times, high energy inputs/costs, and harsh environmental impacts. Embodiments of the present disclosure address this need as well as other needs that will become apparent upon reading the description below in conjunction with the drawings. 
     The world&#39;s oceans contain considerable amounts of lithium. In fact, the amount of lithium present in the world&#39;s oceans is around 16,000 times greater than the amount of land-based lithium. Additionally, extracting lithium from seawater would not be subjected to the geographic limitation of in-ground lithium sources. Although &gt;99.9% of the world&#39;s lithium exists in the ocean, the dilute lithium ion concentration (varying around 0.1 to 0.2 ppm) greatly increases the difficulty of the recovery process. Moreover, the coexistence of other ions, such as sodium ions, having molar concentrations several orders of magnitude larger than the lithium ion concentration, adds an additional level of complication to any extraction process. Disclosed herein, therefore, are systems and methods to improve the extraction of lithium ions from seawater through an electrochemical process. The present disclosure can utilize the different electrochemical characteristics of lithium and sodium ions in saltwater. 
     The disclosed technology can include an electrochemical cell for concentrating lithium ions. The electrochemical cell can have two electrodes and a solution therebetween allowing for ion and fluid flow between the two electrodes. The solution, saltwater in this example, can contain many ions, such as lithium and sodium. A voltage can be applied to the electrochemical cell to initiate a redox reaction to force the lithium ions to one of the electrodes. The electrochemical cell can also include a molecular sieve disposed on one of the electrodes. The molecular sieve can be configured such that only lithium can pass through to reach the electrode, while preventing the other ions from passing through. In other words, the molecular sieve can aid in concentrating the lithium ions on the electrode while ensuring other ions remain in the solution. Then, the electrochemical cell can be flushed with another solution and the redox reaction can be reversed to transfer the lithium ions from the electrode to the new solution. This new solution can be continually used to collect lithium ions until a desirable concentration is reached. 
     Although certain embodiments of the disclosure are explained in detail, it is to be understood that other embodiments are contemplated. Accordingly, it is not intended that the disclosure is limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. Other embodiments of the disclosure are capable of being practiced or carried out in various ways. Also, in describing the embodiments, specific terminology will be resorted to for the sake of clarity. It is intended that each term contemplates its broadest meaning as understood by those skilled in the art and includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
     Herein, the use of terms such as “having,” “has,” “including,” or “includes” are open-ended and are intended to have the same meaning as terms such as “comprising” or “comprises” and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as “can” or “may” are intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such. 
     By “comprising” or “containing” or “including” is meant that at least the named compound, element, particle, or method step is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, even if the other such compounds, material, particles, method steps have the same function as what is named. 
     It is also to be understood that the mention of one or more method steps does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified. 
     The components described hereinafter as making up various elements of the disclosure are intended to be illustrative and not restrictive. Many suitable components that would perform the same or similar functions as the components described herein are intended to be embraced within the scope of the disclosure. Such other components not described herein can include, but are not limited to, for example, similar components that are developed after development of the presently disclosed subject matter. 
     As used herein, the terms “tissue” and “specimen” can refer to any plurality of biological cells, living or dead, and/or any number of other biomaterials, including, but not limited to, any single instance or plurality of bones, organs, muscles, and the like. 
     Reference will now be made in detail to exemplary embodiments of the disclosed technology, examples of which are illustrated in the accompanying drawings and disclosed herein. Wherever convenient, the same references numbers will be used throughout the drawings to refer to the same or like parts. 
       FIG. 1  illustrates a system  100  for concentrating ions. The system  100  can comprise an electrochemical cell including a first electrode  110 , a second electrode  120 , and a first solution  130  in fluid communication with the first electrode  110  and the second electrode  120 . As shown, the first solution  130  can have a plurality of ions. In particular, the first solution  130  can have a first ion  132  (e.g., a target ion) and a second ion  134  (e.g., a non-target ion). It is understood that the first solution  130  can have multiple non-target ions, and that the first solution  130  can also have multiple target ions. For example, the first ion  132  (e.g., the target ion) can be lithium, and the second ion  134  (e.g., the non-target ion) can be sodium. In such an example, any other ions remaining in the first solution  130  can be a non-target ion. 
     The system  100  can also include a molecular sieve  210  disposed on the first electrode. The molecular sieve  210  is shown in greater detail in  FIGS. 2A and 2B . The molecular sieve  210  can be configured to selectively permit the first ion  132  (e.g., the target ion) to pass through the molecular sieve  210  to move between the first solution  130  and the first electrode  110 . The molecular sieve  210  can also be configured to selectively prevent the second ion  134  (or any number of non-target ions) from passing from the first solution  130  to the first electrode  110 . The molecular sieve  210  can be any material that is nonreactive in the electrochemical cell that can create enough steric hinderance to non-target ions while allowing target ions to pass through. For example, the molecular sieve  210  can be a polymer or polymeric material. 
     When a voltage is applied to the system  100  to cause a redox reaction in the electrochemical cell, the ions from the first solution can attempt to migrate to the first electrode  110  (or the second electrode  120 , depending on the polarity of the voltage). In such a manner, the first ion  132  can be the only ion to pass through the molecular sieve  210  to the first electrode  110 . The remaining ions can therefore be rejected by the molecular sieve  210 , remaining in the first solution  130 . In such a manner, the first ion  132  (e.g., the target ion) can be concentrated at the first electrode  110 . 
     Referring again to  FIG. 1 , the system  100  can further comprise a voltage source  140  that can apply a differential voltage between the first electrode  110  and the second electrode  120 . The voltage source  140  can be any device or component configured to create an electric potential, such as a battery, a power outlet, and the like. As described above, the differential voltage can cause the electrochemical cell to undergo a redox reaction. The redox reaction can cause the first ion  132  to absorb into the first electrode  110 . 
     Furthermore, the system  100  can comprise a second solution  150 . The second solution can be brought into contact with the first electrode  110  such that the first ion  132  is desorbed from the first electrode  110  and into the second solution  150 . Because the redox reaction causes the first ion  132  to be absorbed into the first electrode  110 , and because the molecular sieve  210  prevents the second ion  134  (and other non-target ions) from reaching the first electrode, the second solution  150  can therefore become concentrated with the first ion  132  (e.g., the target ion). In some examples, once the first ion  132  is desorbed from the first electrode  110  and into the second solution  150 , the second solution  150  can be removed from the system  100  to allow the first solution  130  to be added once again, thereby repeating the process. An example of such a process is described in greater detail below in  FIG. 3 . 
     Although  FIG. 3  is described with respect to being performed by the system  100 , it is understood that the disclosure is not so limited. Indeed, some or all of the steps shown in  FIG. 3  can be performed by other components of the system  100  or other similar systems. 
       FIG. 3  is a flowchart of a method  300  of concentrating ions. As shown, in block  310 , the system  100  can contact the first solution  130  to the electrochemical cell. As described above, the first solution  130  can have a first ion  132  and a second ion  134 . The electrochemical cell can have a first electrode  110 , a second electrode  120 , and a molecular sieve  210  disposed on the first electrode  110 . The molecular sieve  210  can be configured to selectively permit the first ion  132  to pass from the first solution  130  to the first electrode  110 . The method  300  can then proceed on to block  320 . 
     In block  320 , the system  100  can apply a first differential voltage to the electrochemical cell. The first differential voltage can be provided by the voltage source  140 . The first differential voltage can be applied between the first electrode  110  and the second electrode  120 , causing the electrochemical cell to undergo a redox reaction. The redox reaction can cause the first ion  132  to absorb into the first electrode  110 . The method  300  can then proceed on to block  330 . 
     In block  330 , the system  100  can contact a second solution  150  with the electrochemical cell. This can be performed after the first solution  130  is flushed out of the electrochemical cell. Because the redox reaction causes the first ion  132  to be absorbed into the first electrode  110 , and because the molecular sieve  210  prevents the second ion  134  (and other non-target ions) from reaching the first electrode, the second solution  150  can therefore become concentrated with the first ion  132 . The method  300  can then proceed on to block  340 . 
     In block  340 , the system can apply a second differential voltage to the electrochemical cell. The second differential voltage can be provided by the voltage source  140 , and the second differential voltage can be of opposite polarity to the first differential voltage. The second differential voltage can be applied between the first electrode  110  and the second electrode  120 , thereby causing the electrochemical cell to reverse the redox reaction cause by the first differential voltage. In such a manner, the first ion  132  can be desorbed from the first electrode  110  and into the second solution  150 . The method  300  can then terminate after block  340 . In some examples, however, once the first ion  132  is desorbed from the first electrode  110  and into the second solution  150 , the second solution  150  can be removed from the system  100  to allow the first solution  130  to be added once again, thereby repeating the method  300  from block  310 . 
     Certain embodiments and implementations of the disclosed technology are described above with reference to block and flow diagrams of systems and methods and/or computer program products according to example embodiments or implementations of the disclosed technology. It will be understood that one or more blocks of the block diagrams and flow diagrams, and combinations of blocks in the block diagrams and flow diagrams, respectively, can be implemented by computer-executable program instructions. Likewise, some blocks of the block diagrams and flow diagrams may not necessarily need to be performed in the order presented, may be repeated, or may not necessarily need to be performed at all, according to some embodiments or implementations of the disclosed technology. 
     While the present disclosure has been described in connection with a plurality of exemplary aspects, as illustrated in the various figures and discussed above, it is understood that other similar aspects can be used, or modifications and additions can be made to the described aspects for performing the same function of the present disclosure without deviating therefrom. For example, in various aspects of the disclosure, methods and compositions were described according to aspects of the presently disclosed subject matter. However, other equivalent methods or composition to these described aspects are also contemplated by the teachings herein. Therefore, the present disclosure should not be limited to any single aspect, but rather construed in breadth and scope in accordance with the appended claims. 
     EXAMPLES 
     Example 1 
     To better understand the interaction between lithium ions and sodium ions in seawater, an electrochemical cell was build containing lithium iron phosphate (LFP) as the working electrode, platinum wire as a counter electrode, and a Ag/AgCL electrode as a reference electrode to test the electrochemical properties under various electrochemical environments. The cell was firstly discharged in pure lithium solution (0.1M LiCl), pure sodium solution (0.5M NaCl), or a mixture of lithium and sodium (0.1M LiCl+0.5M NaCl), which can artificially simulate the seawater condition where 0.5M NaCl is the nominal sodium concentration, to distinguish the potentials according to the intercalation of different ions. 
     As shown in  FIG. 4 , the difference in the discharge curve among the three different solutions can be clearly seen. In the lithium solution, the flat plateau at 0.05V can correspond to lithium intercalation. In the sodium solution, the tail below −0.15V can correspond to the sodium intercalation. However, two plateaus can be observed in the artificial seawater solution, indicating the co-intercalation of both ions onto the LFP. The reactions of the LFP electrode during discharge in the different electrolytes are shown in Equations 1, 2, and 3, respectively. 
       In 0.1M LiCl solution: FePO 4 +Li +   +e   − →LiFePO 4   (1)
 
       In 0.5M NaCl solution: FePO 4 +Na +   +e   − →NaFePO 4   (2)
 
       In artificial seawater: FePO 4   +x Li + +(1 −x )Na +   +e   − →Li x Na 1−x FePO 4   (3)
 
     The intercalation of sodium onto the LFP can reduce the lithium storage capability because of the competitive relationship of the two ions. Moreover, the olivine structure of the electrode can gradually transform to the thermodynamically preferable maricite structure induced by the insertion of sodium. Thus, the electrochemical reversibility of the LFP can be compromised, blocking the lithium diffusion channels. 
     Crown ethers can be used to synthesize a lithium-selective polymer to act as an ion-sieve to allow lithium to pass but block sodium. Several types of lithium-selective ionophores can be used, and crown ethers can be used in particular due to their great capability to capture alkali metal cations thanks to the strong binding ability of the oxygen atoms. This can be based at least in part on the hard-soft and acid-base concept, without wishing to be bound by any one particular scientific theory. The ion-selectivity of crown ethers can be mostly based on the cavity size, where lithium can be mostly favorable to fit into the 14-member ring macrocycle (14-crown-4) from the examination of CPK space-filling models. Adding a benzyl group to the 14-crown-4, 6,6,-Dibenzyl-14-crown-4 can exhibit outstanding lithium selectivity, because introducing bulky substituents into the host ionophore can effectively suppress the formation of 2:1 or 3:1 sandwich-type ionophore-cation complexes with larger sized cations, such as sodium. 
     The lithium ion-selective molecular sieve can contain 1.5% by weight of lithium ionophore VI (6,6,-Dibenzyl-14-crown-4), 0.5% by weight of potassium tetrakis(4-chlorophenyl)borate (KTCIPB), 28% by weight of polyvinylchloride (PVC), 68.5% by weight of 2-nitrophenyl octyl ether (NPOE), and 1.5% by weight of trioctylphosphine oxide (TOPO). The molecular sieve can be prepared by dissolving 100 mg of the mixture in 1 ml of tetrahydrofuran (THF) and stirred for 12 hours. The molecular sieve can then be prepared by casting the lithium-selective polymer on a polytetrafluoroethylene (PTFE) evaporating dish and placed in a fume hood for 24 hours to let the solvent fully evaporate. 
     To further understand the effect of the molecular sieve, a simulation of the steric energy of the intermediate states of the 6,6-Dibenzyl-14-crown-4 binding with lithium and sodium were performed. As shown in  FIGS. 5A and 5B , respectively, each simulation run had the test ions of the same species set at both sides of the crown ether to be converged to the lowest energy point (stable point). The lithium spontaneously can pass through the cavity of the crown ether from the right to the left to reach the stable point. However, the sodium ion is blocked by the cavity from both sides due to the high energy barrier that occurs when sodium is in the center of the cavity. In such a manner, the simulations can demonstrate the efficacy of the molecular sieve toward a high selectivity of lithium over sodium. 
     To further dispose the molecular sieve onto the electrode, the molecular sieve can be coated onto the LFP electrode and surface treated. First, the LFP powder can be mixed with a conductive additive (carbon black) and a binder (polyvinylidene fluoride) to prepare the electrode slurry. Then, the slurry can be covered on carbon cloth to form the LFP electrode. Subsequently, the LFP electrode can be dipped into a molecular sieve solution to form the molecular sieve layer on the surface of the electrode. In such a manner, the surface treated LFP (STLFP) electrode can be formed. 
     After forming the STLFP, the electrode can be placed in an electrochemical cell to test electrochemical performance. The electrode can be first placed in a cell full of artificial seawater and started to extract lithium. As shown in  FIG. 6 , unlike LFP, the discharge curve of STLFP does not show the plateau after −0.15V, which corresponds to sodium intercalation. The single-plateau discharge curve of the STLFP can be attributed to the molecular sieve coating, indicating that the sodium intercalation can be greatly inhibited. Upon reaching the cutoff voltage (−0.2V), the electrode can be transferred to another cell, which can contain the recovery solution (0.1M KCl) to release the captured ions by charging. 
     The recovery solution can be tested by ICP-ES to further confirm the effects of the molecular sieve coating. According to the ICP-ES measurements, the results can demonstrate the selectivity of the STLFP can be improved by a factor of 3.15. The molar ratio of lithium to sodium in the recovery solution can be 0.68 using the LFP and 2.15 using the STLFP, as shown in  FIG. 7 .