Continuous Direct Lithium Extraction from Seawater Via an Unconventional Selective Solid Electrolyte

Abstract

With the significant depletion of terrestrial lithium resources, attention has shifted toward seawater, which holds the largest lithium reserves on Earth. However, extracting lithium from seawater presents a complex challenge due to its intricate composition and extremely low concentration of lithium ions. Herein, we demonstrated inexpensive Li4Ti5O12 as a selective solid electrolyte for direct lithium extraction from seawater. It extracted lithium ions from seawater at an initial concentration of 0.17 mg/L and enriched them to 22.25 mg/L in the receiving solution. The sodium and magnesium ion concentrations were only 33.5 mg/L and 0.66 mg/L. The Li/ Na selectivity (SLi/Na) and Li/Mg selectivity (SLi/Mg) were remarkably high, reaching 42,000 and 240,000, respectively. Furthermore, DFT showed that the energy required for both processes-desolvation of sodium ions and migration of ions within the crystal-is significantly higher than that for lithium ions, which explains the high selectivity of this method. XAS and XRD refinement revealed that the lithium-ion conductor remained stable without any decomposition. In addition, we designed a comprehensive process using the phase equilibrium method, enabling the direct separation of lithium hydroxide without waste when Li4Ti5O12 serves as the selective solid-state electrolyte, thereby highlighting its strong potential for industrial applications.