An Electrochemical Cell for Selective Lithium Capture from Seawater

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An Electrochemical Cell for Selective Lithium Capture from Seawater Joo-Seong Kim, Yong-Hee Lee, Seungyeon Choi, Jaeho Shin, Hung-Cuong Dinh, and Jang Wook Choi Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b00032 • Publication Date (Web): 29 Apr 2015 Downloaded from http://pubs.acs.org on May 7, 2015

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Environmental Science & Technology

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An Electrochemical Cell for Selective Lithium

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Capture from Seawater Joo-Seong Kim,†,§ Yong-Hee Lee,†,§ Seungyeon Choi,† Jaeho Shin,‡ Hung-Cuong Dinh,∥,⊥ and Jang Wook Choi†,*

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†

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Graduate School of Energy, Environment, Water, and Sustainability (EEWS) and Center for Nature-inspired Technology (CNiT) in KAIST Institute NanoCentury, ‡

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Department of Chemical and Biomolecular Engineering,

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Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu,

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Daejeon 305-701, Republic of Korea ∥Laboratory

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for Materials and Engineering of Fibre Optics, Institute of Materials Science

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(IMS), Vietnamese Academy of Science and Technology (VAST), 18 Hoang Quoc Viet road,

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Cau Giay District, Hanoi, Vietnam ⊥International

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Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for

Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Japan

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§

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*Corresponding author: (e-mail) [email protected], (phone) +82-42-350-1719, (fax)

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+82-42-350-2248

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These authors contributed equally.

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Abstract

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Lithium (Li) is a core element of Li-ion batteries (LIBs). Recent developments in

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mobile electronics such as smartphones and tablet PCs as well as advent of large-scale LIB

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applications including electrical vehicles and grid-level energy storage systems have led to an

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increase in demand for LIBs, giving rise to a concern on the availability and market price of

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Li resources. However, the current Lime-Soda process that is responsible for greater than 80%

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of worldwide Li resource supply is applicable only in certain regions on earth where the Li

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concentrations are sufficiently high (salt lakes or salt pans). Moreover, not only is the process

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time-consuming (12~18 months), but post-treatments are also required for the purification of

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Li. Here, we have devised a location-independent electrochemical system for Li capture,

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which can operate within a short time period (a few hours to days). By engaging olivine

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LiFePO4 active electrode that improves interfacial properties via polydopamine coating, the

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electrochemical cell achieves 4330 times amplification in Li/Na ion selectivity (Li/Na molar

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ratio of initial solution = 0.01 and Li/Na molar ratio of final electrode = 43.3). In addition, the

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electrochemical system engages an I-/I3- redox couple in the other electrode for balancing of

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the redox states on both electrode sides and sustainable operations of the entire cell. Based on

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the electrochemical results, key material and interfacial properties that affect the selectivity in

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Li capture are identified.

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Introduction

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The development of rechargeable lithium ion batteries (LIBs) has brought the advent

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of revolutionary changes in energy storage technology.1-3 A wide spectrum4-9 of electronics

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ranging from mobile IT devices to electric vehicles utilize LIBs due to their relatively high

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energy densities, resulting in a gradual increase for the demand of lithium (Li) resources.

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However, Li, the core element of LIB, exists in a finite amount in nature and can only be

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produced in limited regions in the world. Due to this maldistributed supply, the price for Li is

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steadily rising.10 In these respects, the development of low-cost and rapid production

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processes is desirable for stable Li supply to relevant industries.11,12 Currently, the Lime-Soda

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evaporation process used in salt lakes or salt pans is responsible for the major portion of

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worldwide Li supply (more than 80%). However, this process is not only time-consuming

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(12~18 months), but also applicable solely to highly concentrated areas. Furthermore,

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additional processes for removing residual ions are required before obtaining final products.13

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To overcome these drawbacks, many researchers have developed alternative systems

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for Li capture, including Al2O3 process, ion exchange methods, selective membrane

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technology, etc.14-17 Nevertheless, many of these systems lack feasibility due to their low

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ionic selectivity and limited working conditions (concentration, pH, etc.). The

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electrochemical method has also lately received discernable attention targeting Li capture

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from seawater due to its ability to capture and recover Li in a short time with relatively small

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purification steps. It should be, however, noted that despite the massive quantity available

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from the ocean, Li capture from seawater is extremely challenging because only a trace

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amount of Li (~0.183 ppm) is present in the given volume and this condition would require a

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high standard in the selectivity of Li over other cations, especially sodium (Na) ion (~10.8

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ppm). For this reason, LIB cathode materials have been counted18,19 as unique candidates for 3 ACS Paragon Plus Environment


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Li capture since their well-defined ionic channel dimensions could expel other cations with

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larger diameters. In fact, lithium iron phosphate (LiFePO4, or LFP) under the olivine

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framework18,20-22 and lithium manganese oxide (LiMn2O4, or LMO)7,19,23,24 exhibited

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promising Li capture capabilities. Nonetheless, these investigations leave a room for further

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improvement, as a majority of them rely on expensive silver/silver chloride (Ag/AgCl)

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counter electrodes that are difficult to avoid Ag+ dissolution. In the structural viewpoint,

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LMO holds an advantage that Li is located at the tetrahedral sites with the limited space,

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which is beneficial for the selectivity over other bigger cations. However, the operating

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voltages of LMO make it hard to avoid water splitting completely, lowering the efficiency of

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the overall system.

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In the present investigation, we have built a highly selective and reversible Li capture

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system by constructing an electrochemical cell that overcomes the existing limitations. As an

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active electrode material, LFP was chosen due to its appropriate working potentials within

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stable windows of water at all pHs25 as well as its structural advantages for the selectivity

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over Na ion. Also, mussel-inspired polydopamine (pD) was used to coat LFP powder to

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control interfacial energy penalty and thus the ionic selectivity. Moreover, a reversible I-/I3-

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redox couple was engaged in the working electrode (WE) to facilitate the redox reaction in

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the LFP counter electrode (CE) in a sustainable fashion. With this newly devised system, the

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present study pays attention to the interfacial and electrode material properties that affect the

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selective Li capture.

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MATERIALS AND METHODS

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Synthesis of c-FePO4. To synthesize pristine LFP, a hydrothermal method was used. 60 4 ACS Paragon Plus Environment

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mmol of lithium hydroxide (LiOH) was dissolved in 40 mL of ethylene glycol, and the

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dispersion was stirred for 1 h. 20 mmol of FeSO4·7H2O was separately dissolved in 12 mL of

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deionized water, and this solution was stirred for 15 min. These two solutions were mixed,

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followed by introduction of 20 mmol of H3PO4. Next, 0.879 g of L-ascorbic acid and 3.0 g of

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P123 were dissolved in 10 mL of deionized water, which was then added to the mixed

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solution. The solution was briskly stirred for 2 h until gray suspension was made. The

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suspension was transferred into a 100 ml Teflon-lined stainless-steel autoclave, and

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hydrothermal reaction was carried out at 180 °C for 12 h. After the reaction, using

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centrifugation, precipitant was collected and washed by co-solvents of water and ethanol (9:1

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in volume) several times, which was followed by a drying step in a vacuum oven for 24 h.

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For the conformal carbon coating on LFP powder, 3.5 g of LFP and 1.5 g of sucrose

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were added to 40 mL of deionized water, followed by stirring for 30 min. The suspension was

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then transferred into a 100 mL Teflon-lined autoclave, and hydrothermal reaction was carried

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out at 180 °C for 12 h. After the reaction, precipitant was collected using centrifugation and

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washed by deionized water several times. The precipitant was then dried inside an oven for

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24 h. The dried powder was heated at 600 °C for 1 h in a nitrogen atmosphere.

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For chemical extraction of Li from c-LFP, an oxidizing solution was prepared by

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dissolving 1.7 g of nitronium tetrafluoroborate (NO2BF4) in 100 mL of acetonitrile. 1.0 g of

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c-LFP powder was immersed into the solution and stirred for 24 h at room temperature. The

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powder was then washed several times by acetonitrile and finally dried in a vacuum oven for

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12 h.

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Surface Modification of c-FePO4 with Polydopamine. The surface of c-FP was coated with

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polydopamine by immersing the synthesized c-FP powder in a solution composed of 5 ACS Paragon Plus Environment


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dopamine chloride with various relative contents of 5~50% compared to c-FP in weight. The

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solution contained methanol and tris-buffer solution in a 1:1 volume ratio as a solvent while

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the overall pH was fixed to 8.5. After overnight stirring, the pD-coated c-FP (denoted as pD-

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c-FP) was washed several times with methanol and dried in a vacuum oven for 12 h. All

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reagents were purchased from Sigma-Aldrich and used without purification.

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Reversible Electrochemical System. Performance tests of the reversible Li capture system

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were conducted by using a home-built 3-electrode system. Iodine solution (0.5 M in

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acetonitrile) and battery composite electrode were used as a working and a counter electrode,

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respectively. Ag/AgCl electrode was chosen as a reference electrode (RE) and various

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concentrations of brine were used as the electrolyte (Li: Na = 1: 100 molar ratio).

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Cell Preparation. For preparation of the active electrodes, active material, binder, and

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conductive agent were dispersed in N-methyl-2-pyrrolidone (NMP, Sigma-Aldrich) in a

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weight ratio of 8:1:1. pD-c-FP and c-FP were used as active materials. Poly-vinylidene

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fluoride (PVDF, Kynar) and denka black were used as a binder and a conductive agent,

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respectively. The well-mixed slurries were cast onto SUS 316 plate using the doctor blade

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technique and the cast electrodes were dried in a vacuum oven at 90 °C for 12 h.

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Material Characterization. Contact angle measurements (Drop shape analysis system,

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Phoenix 300, Korea) were carried out by dropping a deionized water droplet on the surface of

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the electrode. The crystal structures of materials were characterized by X-ray diffraction

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(RIGAKU, D/MAX-IIIC). Li/Na contents of the electrodes were measured by inductively

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coupled plasma atomic emission spectrometry (ICP-AES).

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Electrochemical Measurements. The electrochemical properties of the electrodes as LIB

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cathodes were galvanostatically tested in a 3-electrode system in the potential range of 6 ACS Paragon Plus Environment

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0.3~0.6 V (vs. Ag/AgCl) using a battery cycler (Bio-Logic VSP). Platinum mesh and

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Ag/AgCl were used as the counter and the reference electrodes, respectively. For cycling tests

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of Li capture-recovery, the c-FP-based electrodes were tested in the same voltage window

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under the constant current mode using the same equipment. The current density in both

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measurements was 0.184 mA/g, and the mass of c-FP only was taken into account for the

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calculation of the current density and specific capacity.

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RESULTS

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In order to fully utilize the attractive features of electrochemical approaches for Li

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capture, it is crucial to grasp the inherent properties of seawater in actual oceanic

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environments. In general, seawater has a pH in the range of 7.5~8.4 and contains various salts

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that amount to 3.5%. These salts consist mainly of alkali metal elements (Group I) and

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alkaline earth metal elements (Group II) as summarized in Supporting Table S1.26,27 Among

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these, Li ranks the 6th in abundance, but this value is far smaller than that of Na, as the Li-to-

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Na molar ratio is as small as ~1/18000. The inherently low concentration of Li requires a

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preliminary step that gets rid of other ions as much as possible.

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In this pre-treatment viewpoint, it is notable that the ionic radii of some elements

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from the Group I and II are quite similar (see both columns in Supporting Table S2).28 Hence,

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it is difficult to separate them based solely on their sizes. Nevertheless, an alternative method

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that uses chemical precipitation and filtration allows one to selectively remove divalent ions.

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In detail, separation of divalent ions is feasible through the use of differences in solubility

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when combined with (bi)carbonate salts (Supporting Table S3). In the given processes, salts

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with divalent ions bonded to bicarbonate are primarily precipitated. Also, by using the 7 ACS Paragon Plus Environment


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hydration energy difference between the two groups of elements, monovalent ions can be

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separated through a membrane (Table S4).29 As these preliminary steps have already been

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established, our main task in the current investigation lies not with the separation of Li from

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pristine seawater, but with the search for optimal conditions focusing on monovalent cations

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through an electrochemical process. The present research was designed to confirm the

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operational viability of our electrochemical cell as well as to identify critical parameters that

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influence the selectivity in Li capture over Na ion.

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In order to electrochemically capture Li in seawater conditions, the active material

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for the electrode must have a stable redox potential window under the seawater conditions.

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As can be seen in Figure 1a, seawater usually has a pH range of 7.5~8.4, and the operating

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window of LFP fits in the stable window of water at this pH range. In particular, LFP

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possesses 1-D diffusion channels that grant facile Li ion insertion into octahedral sites.20-22

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Also, the absence of electrolysis makes LFP an attractive material for stable Li capture.

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However, pristine LFP has an intrinsic low electric conductivity with slow kinetics for Li-ion

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diffusion, resulting in rather inferior electrochemical activity. In addressing this inherent flaw,

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LFP was coated with carbon (c-LFP) using sucrose as a carbon precursor, leading to

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increased electrochemical activity. To serve as an active electrode material in the Li capture

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system, Li was chemically extracted by using NO2BF4 to turn c-LFP to c-FP. c-FP still has

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another issue of wettability in aqueous electrolytes due to the hydrophobic nature of the

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carbon-coating layer. Thus, polydopamine (pD) with hydrophilic functional groups was used

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to coat the prepared c-FP powder (pD-c-FP, Figure 1b right) to enhance its wettability in

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aqueous environments. pD-c-FP turned out to offer improved electrochemical performance in

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aqueous electrolytes as compared to the counterpart without the pD coating, as pD-c-FP

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exhibited larger capacities, smaller overpotentials, and better cycling performance 8 ACS Paragon Plus Environment

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(Supporting Figure S1).

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Another trait that benefits LFP for this Li capture system is that its structure

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promotes the selective capture of Li ions over Na ions. It can be seen that LFP has an olivine

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structure (Figure 1c, left). After Li has been chemically removed, FP can still exist as an

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olivine structure (Figure 1c, middle). In terms of volume change, the volume expansion

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(17.8%) after Na ion insertion is significantly larger than that (7.5%) after Li ion insertion,

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making the Li ion insertion energetically more favorable (Supporting Figure S2a). Moreover,

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the diffusion energy of Na ions within the FP lattice is 119 meV higher than that of Li ions,30

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indicating that Li ion diffusion within the olivine framework is more thermodynamically

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favorable. But, upon the insertion of Na ions, the olivine structure of FP is preferably

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transformed to a maricite structure (Figure 1c, right) because the maricite phase has a 16 meV

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lower formation energy (Supporting Figure S2b).31 The maricite phase can be described with

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the chemical formula FeNaPO4, a structure in which site exchange occurs with M1 sites for

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alkali metal and M2 sites for iron, inevitably lowering the reversibility. Accordingly, the

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maricite formation at local spots in each particle blocks Li ion diffusion channels, thereby

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decreasing the capturing capacity (Supporting Figure S2c).32

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For the practical viability of the devised system in this work, an electrochemical

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system that affords reversibility without the loss of electrode material is also equally

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important to the aforementioned effort with regard to the Li capturing electrode. To this end,

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we have opted for the I-/I3- redox couple, whose reversibility has previously been confirmed

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in dye-sensitized solar cells33 and Li-I batteries34, in the other electrode. Our reversible

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electrochemical system is schematically described in Figure 1d. In this system, pD-c-FP or c-

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FP, the I-/I3- redox couple, and Ag/AgCl constitute the CE, WE, and RE, respectively. The Li

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capture process was operated under constant current between the WE and the CE (1.3 mA, 9 ACS Paragon Plus Environment


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0.3C) for 5 h. The entire chemical reaction during the current supply is given as follows:

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3I- + 2Li+ + 2FePO4 ↔ I3- + 2LiFePO4

(1)

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When current was applied between the WE and the CE, I- was oxidized to I3- while FP was

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reduced to yield LFP by reacting with Li ions, resulting in a capture of Li ions within the FP

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lattice. The reversibility of this system was verified in Supporting Figure S3.

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In order to elucidate the surface coating effect on the selectivity, the amount of pD

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coating was varied (5, 10, 20% pD relative to c-FP in weight). To examine the selectivity, the

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electrodes were analyzed after Li capture by using X-ray diffraction (XRD) (Figure 2a). In

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the Li capture experiment, 0.005 M LiCl was added to a 0.5 M NaCl solution as the

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electrolyte to make a Na/Li molar ratio 100. After the given current supply (1.3 mA, 5 h), the

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5% pD-c-FP electrode showed XRD peaks that are well-aligned with those of pristine LFP,

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implying the original FP is fully lithiated and its selectivity over Na ion is good. However,

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with a 10% pD-c-FP electrode, XRD results exhibited peaks assigned to NaFePO4 (NFP),

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indicating the presence of partial Na ion insertion into the electrode. Also, as the pD amount

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was increased further, so did the intensity of NFP peaks in the XRD results, revealing

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increased Na ion co-insertion into the electrode proportionally to the pD amount.

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This pD concentration dependence can be explained through improved wettability

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from pD coating. As displayed in Figures 3a-b and S4, the increased pD concentration indeed

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enhances the wettability of the electrode surface. Although the small pD concentration would

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result in uniform pD coating around c-FP particles because of the well-known coating

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capability of dopamine polymerization process,35-37 the electrode composition including a

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carbon conductive agent with a good volume occupation makes a difference in the wettability

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of the electrodes with different pD concentrations. 10 ACS Paragon Plus Environment

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During the electrochemical cation capture, cations in the electrolyte pass through the

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electrode-electrolyte interface and are inserted into the electrode. For this to occur, two types

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of energy are required at the interface: dehydration energy that can strip water molecules

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from the cations and insertion energy that allows the cations to insert into the electrode lattice.

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In this respect, the enhanced wetting by the hydrophilic pD coating increases the ion

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concentration at the electrode surface and thus the chance for the insertion, although the

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dehydration energy is still required for the insertion of each Na ion. The effect of pD coating

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can be mathematically interpreted by the Gibbs-Lippmann equation (2), an expression that

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relates the properties of the electrode surface and the electrolyte:

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−dγ = qdE- + Γ+dµ

(2)

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This equation describes the rate of change in interface energy (dγ), in correlation with the

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interface charge density (q) and differential potential of electrode (dE), and the excess

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concentration (Γ+) of cation at the electrode surface and changes in electrochemical potential

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(dµ). At a constant current condition that gives stable voltage (Figure S5), dE can be assumed

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zero. Then, the above equation can be rearranged to the equation (3) in terms of excess

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electrolyte concentration at the electrode surface:

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Γା = − ቀ ቁ

பஓ

பஜ ா ష

(3)

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This equation implies that at the given electric bias (fixed E), higher excess ionic

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concentration allows the interfacial energy of the cation to respond more sensitively to the

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electrochemical potential change. In the actual cell operation, this equation can be equally

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applied in a way that the excess ion concentration at the electrode surface makes cation

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insertion into the electrode more facile through its enhanced interfacial energy. Based on this

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relation, the enhanced wettability has a critical effect on the Li/Na ion selectivity. As 11 ACS Paragon Plus Environment


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portrayed in Figure 3e, upon the insertion, energy barriers along the ionic channels need to be

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overcome for ionic diffusion inside the lattice. For this insertion, the Na ion case requires

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further energy penalty as reflected by the larger volume expansion of the FP lattice compared

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with that of the Li ion insertion. Na ions should also overcome higher energy barriers for

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their inner diffusion. These two phenomena are described by energy gap for ‘phase transition

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and ion diffusion’ in Figure 3e. Even in the existence of this structural preference toward the

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Li ion diffusion, however, the increased (excess) ionic concentrations (both Li and Na ions,

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the higher relative energy levels in the diagram) after the increased pD coating amount allow

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Na ions to overcome the relative structural disadvantage and co-insert into the lattice based

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on the equation (3), explaining the partial co-intercalation of Na ions in the case of 20% pD-

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c-FP.

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This interpretation was validated further when the NaCl concentration was varied. As

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the Na ion concentration was increased from 0.5 M to 3.0 M while the Li/Na molar ratio was

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fixed to 0.01, more serious Na ion co-intercalation was detected in XRD spectra (Figure 4).

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Similar to Figure 3e, these phenomena can be understood based on the excess ion

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concentration and the distinct diffusion barrier as well as the required energy for the phase

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transition. Distinct dehydration energy between Na and Li ions may be taken into account in

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a way that the Li ion requires higher dehydration energy due to its smaller ionic radius. As

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graphically illustrated in Figure 5a, at all NaCl concentrations, the energy levels of Li ions in

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the electrolyte are lower due to its lower concentrations. At the interface, once again, Na ions

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spend less dehydration energy (orange arrows vs. green arrows of the Li ion case). After the

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insertion, the higher inner diffusion barriers and the larger phase transformation energy make

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Na ion diffusion less favorable (red arrows vs. yellow arrows of the Li ion case).

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When a similar environment to seawater using 0.5 M NaCl with a fixed ratio of 12 ACS Paragon Plus Environment

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Na:Li = 100:1 mol% is considered (Figure 5b), the relatively less favorable Na ion diffusion

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within the FP lattice originating from the diffusion barriers and the energy penalty for the

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phase transition (purple arrow) leads to a better Li/Na ion selectivity. In this case, the

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dehydration energy difference between both ions has a minor effect. By contrast, as the NaCl

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concentration is increased (Figures 5c and d), the fouling effect of Na ions becomes serious

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and the relative energy of the Na ions in the electrolyte rises, both of which make Na ion

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insertion relatively more favorable and thus worsen the selectivity. This view is quite

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consistent with the XRD results in Figure 4. Also, the dependence of fouling on the

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concentration can be viewed in a way that the increase in the concentration would transit the

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system more away from the equilibrium, leading to more dynamic fouling environments.

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At the optimal interfacial condition of 5% pD coating, the resultant selectivity and

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insertion efficiency of the electrochemical cell are remarkable. According to ICP analyses

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after Li capture (Figure 6), c-FP and 5% pD-c-FP hold quite distinct selectivities of

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Li/Na=2.64 and 43.3, reconfirming that the properly enhanced wetting facilitates Li ion

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insertion while suppressing Na ion insertion. The selectivity of 43.3 represents 4330 times

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amplification compared to the initial Li/Na ratio of 0.01. The insertion efficiency, defined as

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Li ion occupancy per the available site in the lattice host, was evaluated by Li/Fe molar ratio.

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While the Li/Fe ratio of c-FP is only 0.357, the value of 5% pD-c-FP reaches as high as 0.993,

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indicating that almost all the available sites are indeed occupied by Li ion capture, and the

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given active material is made a full use of. Notably, the selectivity obtained is quite superior

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to those that have been previously reported.18

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Discussion 13 ACS Paragon Plus Environment


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In summary, we have devised an electrochemical system that grants a simple and fast

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process for Li ion capture from brines. It was found that singular changes in either the

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electrode surface or the electrolyte concentration do not provide the optimal condition in the

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selectivity and efficiency. It is rather the interplay between these two variables (5% pD with

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0.5 M NaCl solution) that results in the highest selectivity. Not only do these data serve as

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crucial factors in designing systems and their corresponding parameters for Li capture, but

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they can also be utilized as reference data for applications in an actual oceanic or high

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concentration brine environments. Moreover, the devised system employs an electrode with a

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reversible I-/I3- redox couple in the other electrode, making the overall system sustainable

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without loss of the active electrode material. By integration with established pre-treatment

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schemes, the current electrochemical approach should be applicable to Li capture from actual

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seawater containing diverse ions with different contents.


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Figure 1. The overall strategy for selective Li capture from the ocean. (a) Electrochemical

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stability window of water at different pHs and operating windows of various LIB electrode

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materials. (b) Surface modification of LiFePO4 (LFP) and FePO4 (FP). Synthesized pristine

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LFP (left), carbon-coated FP (c-FP, middle), and polydopamine (pD)-coated c-FP (pD-c-FP,

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right). (c) Structural preference of FP during Li or Na ion captures. Basic structures of LFP

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(olivine), FP (olivine), and FeNaPO4 (maricite). (d) Cell configuration. Li ions are captured

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(left) or released (right) depending the polarity of the applied bias.



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Figure 2. XRD patterns of c-FP and pD-c-FP electrodes after Li capture tests. Reference peak

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locations for pristine LFP (green), FP (orange), and NFP (magenta) are presented in the

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bottom.

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Figure 3. The effect of polydopamine (pD) coating on interfacial properties of c-FP (pD-c-FP)

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powder. Contact angle images of (a) 5% pD-c-FP and (b) 20% pD-c-FP electrodes. Schematic

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illustration of the wettability effect on the ionic insertion in (c) 5% pD-c-FP and (d) 20% pD-

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c-FP particles. (e) A graphical illustration of cation insertion process with different pD

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coating concentrations.



331 332

Figure 4. XRD patterns of 5% PD-c-FP electrodes after Li capture tests. The experiments

333

were conducted in various concentrations of electrolyte (0.5, 1, and 3 M of NaCl with a fixed

334

molar ratio of Li/Na=0.01).

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Figure 5. The effect of electrolyte concentration for selective Li capture. (a) A schematic

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illustration of cation insertion process in various concentrations of cations in the electrolyte.

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Schematic images of the cation insertion process and the fouling effect of concentrated Na

340

ions in (b) seawater condition, (c) brine solution, and (d) highly concentrated brine solution.

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Figure 6. Quantitative molar ratios obtained by inductively coupled plasma (ICP)

344

measurements for various electrode conditions after Li capture.

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ASSOCIATED CONTENTS

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Supporting Information

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Detailed seawater composition, ionic radii, solubility of (bi)carbonate compounds, and

349

hydration enthalpy, additional electrochemical data, phase transition of electrode materials,

350

reversible cell operation, and contact angle images. This material is available free of charge

351

via the Internet at http://pubs.acs.org

352 353

AUTHOR INFORMATION

354

Corresponding Author

355

* E-mail: [email protected]

356

Note

357

The authors declare no competing financial interest.

358 359

ACKNOWLEDGMENT

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J.W.C. acknowledges the financial support by the National Research Foundation of Korea

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(NRF) grant funded by the Korea government (MEST) (NRF-2012-R1A2A1A01011970,

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2012M1A2A2026587, and NRF-2014R1A4A1003712) and Climate Change Research Hub

363

Project of the KAIST EEWS Research Center (N01150039).

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365

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For Table of Contents Only

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An Electrochemical Cell for Selective Lithium Capture from Seawater

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