Friction-differentiated separation of alkali ions through two-dimensional nanochannels based on niobate perovskite

The separation of alkali ions holds profound fundamental significance and immense application potential, particularly driven by the increasing demand for lithium in the era of sustainable energy. Previous approaches relying on the static factor (e.g., size, charge, solubility, adsorption affinities) prove inadequate in the separation of alkali ions due to their highly similar physicochemical properties. By leveraging the difference of friction-an intrinsic factor that incorporates the effects of ion-media correlation with channel or interlayer species during the migration, this work presents a nanofluidic tribology strategy utilizing a platform based on two-dimensional niobate perovskite nanochannels to achieve alkali ions separation. By generating ~42% difference of transport friction at nanonewton-scale, our channels amplify the separation factor between Li⁺/Na⁺ and K⁺/Na⁺ up to 33.1 ~ 45.9, surpassing the state-of-the-art artificial nanochannels by over an order of magnitude. Tuning the channel structural symmetry from herringbone to zigzag type modulates friction-differentiation, achieving a Li⁺ recognized selectivity (Li⁺/K⁺ ~ 28.0). This work establishes a paradigm for separation science through the lens of friction-differentiation and will inspire more advancing technology to secure strategic alkali ion resources critical for a sustainable future.