Direct electrolytic extraction of lithium metal from brines based on sandwich-structured garnet electrolyte

Lithium metal is an important strategic resource with diverse industrial applications such as glass, ceramics, and alloys. With the increasing demand for lithium, lithium extraction from brines has become the focus of attention. However, due to the similarity of the radii of Li + and Mg 2+ , conventional lithium extraction methods are inefficient for lithium extraction from brines with a high Mg/Li ratio. Herein we propose a direct electrolytic extraction of lithium (DEEL) system based on a sandwich-structured LLZTO (Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 ) electrolyte with excellent water stability. The lanthanum zirconate (La 2 Zr 2 O 7 ) on the surface of this sandwich-structured LLZTO can achieve high stability to water and air while still maintaining high ionic conductivity (7.5 × 10 −4  S cm −1 ) and low lithium interface resistance (40 Ω cm 2 ). This sandwich-structured LLZTO has been successfully demonstrated to stably extract lithium from simulated and natural brines. The current density for lithium extraction can reach 0.5 mA cm −2 , corresponding to a lithium extraction rate of 126 μg cm −2  h −1 ; the electrochemical extraction devices can stably work for 48 h; the current efficiency can reach 97.71 %. The extracted lithium metal exhibits a purity of 99.475 wt%. This work provides a highly efficient approach for extracting lithium from brines by electrolysis.