Designing an Intergrowth-Structure Li Ion-Sieve Membrane for Long-Term Stable Lithium Extraction

Extracting lithium from seawater offers an additional Li source but is hindered by corrosion of Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) and weak adhesion of conventional coating layers. Here we propose a permeation growth strategy to construct an intergrowth TiO₂ protection layer on a LAGP membrane (LAGP membrane with intergrowth layer) for long-term stable lithium extraction from seawater. An acidic TiO₂ sol is spin-coated onto a polished LAGP membrane and sintered, during which acid etching and Ti⁴⁺/Ge⁴⁺ ion exchange generate a lattice-matched Li_1+xAl_xTi_2-x(PO₄)₃/LAGP interfacial phase beneath a dense TiO₂ intergrowth layer. This intergrowth-structure eliminates interfacial gaps, enhances peel strength and hardness, and provides continuous Li⁺ transport pathways, delivering an ionic conductivity of 2.40 × 10^-4 S cm^-1 at room temperature and excellent chemical stability in seawater. Applied in a lithium extraction device using natural seawater as anolyte and an organic electrolyte as catholyte, the LAGP membrane with intergrowth layer maintains integrity, Li⁺/Na⁺ selectivity, and stable operation for 650 h, achieving a Coulombic efficiency of 97.4% and an energy consumption of 17.4 kWh kg^-1 _Li. This permeation growth strategy offers a general route to construct intergrowth-structure Li ion-sieve membranes with chemical stability and Li⁺ transport for seawater lithium extraction.