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

ABSTRACT Extracting lithium from seawater offers an additional Li source but is hindered by corrosion of Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) and weak adhesion of conventional coating layers. Here we propose a permeation growth strategy to construct an intergrowth TiO 2 protection layer on a LAGP membrane (LAGP membrane with intergrowth layer) for long‐term stable lithium extraction from seawater. An acidic TiO 2 sol is spin‐coated onto a polished LAGP membrane and sintered, during which acid etching and Ti 4+ /Ge 4+ ion exchange generate a lattice‐matched Li 1+x Al x Ti 2‐x (PO 4 ) 3 /LAGP interfacial phase beneath a dense TiO 2 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.