Lithium Metal Extraction from Seawater

Ping He obtained his PhD in Physical Chemistry from Fudan University in 2009, and later worked as a postdoctoral fellow at the National Institute of Advanced Industrial Science and Technology (AIST), Japan. He currently is a Professor of College of Engineering and Applied Sciences at Nanjing University, China. His research interests focus on electrochemical functional materials and energy storage systems such as lithium-ion batteries and lithium-air batteries. He has published more than 90 peer-reviewed papers.Haoshen Zhou obtained his bachelor’s degree in Nanjing University in 1985, and received his PhD from the University of Tokyo in 1994. He is the prime senior researcher of the National Institute of Advanced Industrial Science and Technology and the professor in Nanjing University. His research interests include the synthesis of functional materials and their applications in Li-ion batteries, Na-ion batteries, Li-redox flow batteries, metal-air batteries, and new types of batteries/cells.Sixie Yang received his bachelor's degree in 2013 and recently received his PhD degree in materials science and engineering at Nanjing University. During his PhD program, he worked in Prof. Ping He and Prof. Haoshen Zhou's research group studying the reaction mechanisms and electrochemistry in Li-air and Li-CO2 batteries. Ping He obtained his PhD in Physical Chemistry from Fudan University in 2009, and later worked as a postdoctoral fellow at the National Institute of Advanced Industrial Science and Technology (AIST), Japan. He currently is a Professor of College of Engineering and Applied Sciences at Nanjing University, China. His research interests focus on electrochemical functional materials and energy storage systems such as lithium-ion batteries and lithium-air batteries. He has published more than 90 peer-reviewed papers. Haoshen Zhou obtained his bachelor’s degree in Nanjing University in 1985, and received his PhD from the University of Tokyo in 1994. He is the prime senior researcher of the National Institute of Advanced Industrial Science and Technology and the professor in Nanjing University. His research interests include the synthesis of functional materials and their applications in Li-ion batteries, Na-ion batteries, Li-redox flow batteries, metal-air batteries, and new types of batteries/cells. Sixie Yang received his bachelor's degree in 2013 and recently received his PhD degree in materials science and engineering at Nanjing University. During his PhD program, he worked in Prof. Ping He and Prof. Haoshen Zhou's research group studying the reaction mechanisms and electrochemistry in Li-air and Li-CO2 batteries. Lithium is one of the most important resources in modern society. Lithium compounds are widely used in many areas, including ceramics, glass, pharmaceuticals, and nuclear industries, and the well-known battery technologies. In recent years, the rapid commercialization of electric vehicles and portable electronic devices has caused significant expansion of the lithium battery market. However, the limited supply of lithium resources may become a problem with the rapid growth of lithium consumption. According to the latest report,1Choubey P.K. Chung K.-S. Kim M.-s. Lee J.-c. Srivastava R.R. Advance review on the exploitation of the prominent energy-storage element lithium. Part II: from sea water and spent lithium ion batteries (LIBs).Miner. Eng. 2017; 110: 104-121Crossref Scopus (170) Google Scholar the proportion of the total global lithium consumption devoted to lithium-ion batteries increased from 31% in 2010 to 43% in 2017 and is estimated to reach 65% by the year 2025. Correspondingly, the demand for lithium resources is continuously growing, which has caused an increase in the price of lithium carbonate in recent years.2Ker P. Lithium Prices Tipped to Rise 20 Per Cent by 2017 on Demand for Electric Cars. The Sydney Morning Herald, 2015http://www.smh.com.au/business/mining-and-resources/lithium-prices-tipped-to-rise-by-20-per-cent-by-2017-on-demand-for-electric-cars-20151026-gkid4z.htmlGoogle Scholar Moreover, based on a very conservative forecast of the future lithium consumption, which only considers the growth of electric vehicles,3Vikström H. Davidsson S. Höök M. Lithium availability and future production outlooks.Appl. Energy. 2013; 110: 252-266Crossref Scopus (525) Google Scholar, 4IEA Technology Roadmap, Electric and Plug-in Hybrid Electric Vehicles 52p. International Energy Agency, 2011Google Scholar the world's annual lithium consumption rate will continue to increase from 2015 to 2050, and 5.11 million tons of lithium will be consumed during this period. This total consumption accounts for more than one-third of the total lithium reserves on land. Based on the consumption rate projected for 2050, the residual lithium reserve on land will be exhausted by 2080 (shown in Figure 1A). Currently all commercial lithium is sourced from ores and brines on land, which contains a total lithium reserve of 14 million tons according to the latest survey conducted this year.5USGS Mineral Commodity Summaries 2017. U.S. Geological Survey, 2017Google Scholar As shown in Figure 1B, the geographic distribution of land-based lithium resources is uneven, with more than 98% of the total reserves concentrated in Chile, Argentina, China, and Australia.5USGS Mineral Commodity Summaries 2017. U.S. Geological Survey, 2017Google Scholar In addition, lithium extraction from ores and brines has a significant environmental impact, including water pollution and depletion, soil damage, and air contamination.6Aral H. Lithium: Environmental Pollution and Health Effects. Elsevier, 2011Google Scholar Clearly, the source of our current lithium supply is unevenly distributed and faces a potential shortage. Hence, the development and utilization of non-conventional lithium sources is important for the future of the lithium battery industry. In contrast, the ocean contains 230 billion tons of lithium, an amount four orders of magnitude larger than the lithium reserves on land (Figure 1).7Diallo M.S. Kotte M.R. Cho M. Mining critical metals and elements from seawater: opportunities and challenges.Environ. Sci. Technol. 2015; 49: 9390-9399Crossref PubMed Scopus (100) Google Scholar Since the amount of lithium in this massive reserve is far higher than the amount consumed annually by human activity, the impact of lithium extraction from seawater on the lithium concentration in the ocean would be negligible. In other words, the omnipresent seawater can act as a nearly infinite global lithium resource, making it a promising source for the future lithium supply. Even though the lithium reserves in the ocean are immense, its concentration in seawater is very low (0.1–0.2 ppm).1Choubey P.K. Chung K.-S. Kim M.-s. Lee J.-c. Srivastava R.R. Advance review on the exploitation of the prominent energy-storage element lithium. Part II: from sea water and spent lithium ion batteries (LIBs).Miner. Eng. 2017; 110: 104-121Crossref Scopus (170) Google Scholar Researchers have proposed several strategies for extracting lithium compounds from seawater, such as adsorption- and dialysis-based methods. Studies have shown that hydrogen metal oxides can adsorb lithium through the exchange of Li+ with H+. In a study reported by Hong et al.,8Hong H.-J. Park I.-S. Ryu J. Ryu T. Kim B.-G. Chung K.-S. Immobilization of hydrogen manganese oxide (HMO) on alpha-alumina bead (AAB) to effective recovery of Li+ from seawater.Chem. Eng. J. 2015; 271: 71-78Crossref Scopus (51) Google Scholar hydrogen manganese oxide (HMO) was employed in the adsorption of lithium from seawater. This material showed a Li+ adsorption capacity of 8.87 mg Li+/g HMO over 6 days. On the other hand, in the dialysis-based methods for lithium extraction, lithium ions are transported from the positive side of the cell to the negative side through a selective membrane driven by an electric field or concentration difference, thus achieving lithium enrichment on one side of the cell. Hoshino reported using an electrodialysis method for lithium concentration with an organic lithium-ion-selective membrane.9Hoshino T. Preliminary studies of lithium recovery technology from seawater by electrodialysis using ionic liquid membrane.Desalination. 2013; 317: 11-16Crossref Scopus (107) Google Scholar In that work, the lithium concentration on the negative side increased from 0% to 22.2% of the lithium concentration in seawater after 2 hr of operation. In another study, Hoshino employed the dialysis method to achieve the concentration of lithium.10Hoshino T. Innovative lithium recovery technique from seawater by using world-first dialysis with a lithium ionic superconductor.Desalination. 2015; 359: 59-63Crossref Scopus (93) Google Scholar After 24 hr of operation, concentrated lithium salt solution (7% of the lithium concentration in seawater) was obtained. Clearly, the lithium extraction rates of the current techniques are relatively slow. In addition, the concentrated lithium is still dissolved in water, and further treatment is required to obtain metallic lithium or solid lithium compounds. Considering the wide use of metallic lithium as the anode material in lithium-sulfur batteries and lithium-air batteries in the future, the current lithium extraction techniques may be too slow and complicated to fulfill the massive demand for metallic lithium. On the other hand, most of the current lithium extraction techniques require an external energy source. If we use solar energy as the power supply and directly extract metallic lithium from seawater, we can simultaneously achieve the recovery of lithium resources and the conversion and storage of solar energy. We report an electrolysis-based technique for extracting lithium from seawater. In our work, a lithium superionic conductor (NASICON)-type solid-state electrolyte is used as the lithium-ion-selective membrane, with an aprotic electrolyte instead of an aqueous solution being employed in the anode side of the cell to create a proton-free compartment. With the help of a specially designed tunable constant current circuit, our prototype device can be powered by a solar panel and metallic lithium can be directly generated during the lithium extraction process. As depicted in Figure 2A, the electrolyte of the electrolysis cell was divided into two parts by the Li1+xAlyGe2−y(PO4)3 (LAGP) solid-state electrolyte, with a LiClO4-propylene carbonate solution in the cathode side and seawater in the anode side. During electrolysis, the cell was charged under constant current by a solar panel. Driven by the electric field, cations in seawater (Na+, Li+…) move from the anode toward the lithium-ion-selective membrane. Owing to the good selectivity of the LAGP membrane,11He P. Zhang T. Jiang J. Zhou H. Lithium-air batteries with hybrid electrolytes.J. Phys. Chem. Lett. 2016; 7: 1267-1280Crossref PubMed Scopus (85) Google Scholar only lithium ions transported to the cathode side and the other cations were blocked and remained in the anode compartment. The electrochemical reactions that can occur on the electrode can be described as follows. On the cathode side, lithium ions are reduced to metallic lithium on the copper foil (Reaction 1); meanwhile, Cl− or OH− is oxidized to Cl2 or O2 on the anode side, and part of the Cl2 may further react with water to form hypochlorite (Reactions 2, 3, and 4).12Oh B.S. Oh S.-G. Jung Y.J. Hwang Y.-Y. Kang J.-W. Kim I.S. Evaluation of a seawater electrolysis process considering formation of free chlorine and perchlorate.Desalin. Water Treat. 2012; 18: 245-250Crossref Scopus (22) Google Scholar, 13Dionigi F. Reier T. Pawolek Z. Gliech M. Strasser P. Design criteria, operating conditions, and nickel-iron hydroxide catalyst materials for selective seawater electrolysis.ChemSusChem. 2016; 9: 962-972Crossref PubMed Scopus (287) Google Scholar A Ru-containing electrode was employed as the anode material to promote the seawater-splitting process.14Hu C.-C. Lee C.-H. Wen T.-C. Oxygen evolution and hypochlorite production on Ru-Pt binary oxides.J. Appl. Electrochem. 1996; 26: 72-82Crossref Scopus (49) Google Scholar The preliminary demonstration device in Figure 2A can be easily rebuilt into a prototype model and scaled up to the industrial level for offshore operation, as shown in Figures 2B and 2C. Cathode:Li + e− → Li(Reaction 1) Anode:Cl− → Cl2 + 2e−(Reaction 2) 2OH− → H2O + 0.5O2 + 2e−(Reaction 3) Cl2 + H2O → HClO + H+ + Cl−(Reaction 4) In a typical lithium extraction procedure, a current of 80 μA (80 μA cm−2 based on the active area of copper foil, the same as below) was applied to the device for 1 hr. During the whole process, the copper foil cathode became metallic gray (inset of Figure 3A) and no gas evolution was observed on either electrode. After the experiment, the copper foil cathode was rapidly transferred to water. In this process, gas was immediately generated and the metallic gray color simultaneously faded. The pH value of the water increased after immersion of the copper foil. We have also conducted X-ray photoelectron spectroscopy (XPS) to characterize the product deposited on the copper foil. Figures 3C and 3D show the XPS of the copper foil after lithium extraction operation. It can be seen in Figure 3C that the lithium salt in the electrolyte, LiClO4, (at ∼57.3 eV)15Morgan W.E. Wazer J.R.V. Stec W.J. Inner-orbital photoelectron spectroscopy of the alkali metal halides, perchlorates, phosphates, and pyrophosphates.J. Am. Chem. Soc. 1973; 95: 751-755Crossref Scopus (322) Google Scholar is the dominant component of the surface layer of the deposit. After using Ar-ion etching to reduce the surface layer, as shown in Figure 3C, a new peak corresponding to metallic lithium appeared (at ∼55.1 eV),16Shek M.L. A soft x-ray study of the interaction of oxygen with Li.Surf. Sci. 1990; 234: 324-334Crossref Scopus (34) Google Scholar demonstrating that lithium is deposited on the copper foil. Meanwhile, no signal of sodium can be detected before or after Ar-ion etching (shown in Figure 3D), indicating that Na+ can be blocked by the selective membrane. X-ray diffraction (XRD) characterization in Figure 3E also showed similar results. Diffraction peaks corresponding to lithium at 36.2°, 52.0°, and 65.0° can be observed after lithium extraction. These results show that metallic lithium can be deposited on copper foil after a lithium extraction procedure. We also conducted three additional lithium extraction experiments with different current magnitudes (160, 240, and 320 μA cm−2) applied to the device each time and used inductively coupled plasma mass spectrometry (ICP-MS) to measure the amount of lithium metal deposited on the cathode. As shown in Figure 3A, the potential-time profiles of the cells electrolyzed under 80, 160, 240, and 320 μA cm−2 currents showed charge potentials of approximately 4.52, 4.75, 4.88, and 5.28 V, respectively. Among the four sets of cells, the 240 μA cm−2 cell showed the best performance. After 1 hr of operation with a 1 cm−2 copper foil as the lithium collector, this cell delivered a lithium production rate of 5.7 mg dm−2 h−1·(Figure 3B), whereas the production rate of the 320 μA cm−2 cell was unusually low, which might be due to the side reaction under high current density. Further study is required to clarify the impact of the current density on the lithium production rate (or energy efficiency) of the lithium extraction device. Seawater can act as one of the next generation of lithium resources for the future lithium mining industry. In this work, we proposed a lithium extraction method based on a solar-powered electrolysis technique with a NASICON solid-state electrolyte as the selective membrane. We showed that the electrolysis method made the lithium extraction process faster and more controllable than in the adsorption- and dialysis-based methods and that it could overcome the limit of the concentration difference that is present in the dialysis method. Moreover, with an aprotic electrolyte in the cathode side, we were able to directly obtain metallic lithium during the lithium extraction process. This method also possesses extensibility. By using different types of ion-selective membrane or anode catalyst material, it may also be able to achieve the recovery of other elements in seawater.