Elevating the Li–Mg Separation Performance of LATP Solid Superionic with Enhanced Local Positive Charge Density

Abstract The existing lithium extraction technologies from salt lakes are confronted with a number of challenges, including limited applicability to brines with elevated Mg/Li ratios and low overall lithium recovery rates. Therefore, it is crucial to develop direct lithium extraction technologies tailored to pristine brines. The core challenge in lithium extraction lies in the effective separation of magnesium and lithium. However, conventional methods struggle to efficiently separate Mg ²⁺ and Li ⁺ in a single‐stage process. Lithium superionic conductors, such as Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ (LATP), are capable of exploiting their internal lithium ion vacancies to enhance the kinetic transport disparity between Mg ²⁺ and Li ⁺ , thus enabling efficient separation. By employing a high‐temperature diffusion technique to introduce Ag ⁺ into the interstitial sites of the LATP lattice, the local positive charge density around Ag ⁺ is increased. This raises the migration barrier for Mg ²⁺ within the LATP, significantly improving the Li–Mg separation performance, with a notable long‐term separation coefficient exceeding 25 000. Using 2% Ag‐doped LATP, battery‐grade Li ₂ CO ₃ with a purity of 99.7% can be produced directly from pristine salt lake brine with a Mg/Li ratio of 500 through a single‐stage separation process.