Fig. 1: Schematic illustration of 2D porous nanosheets as a selective ionic sieve in membrane-based separation and alkali metal-S/Se batteries.

a 2D porous nanosheet-based membranes act as selective ionic sieves in membrane-based separation technologies. The small cations can pass, while large anions are selectively excluded based on a size-sieving effect and electrical interaction between ions and membrane. b 2D nanosheets with sub-nanometer pores act as selective ionic sieves in alkali metal-S/Se batteries. The small Li⁺/Na⁺ ions can rapidly pass through the sub-nanopores, while the large polysulfide/polyselenide (PS) anions are selectively excluded due to size-sieving effect and electrical repulsion between PS anions and negatively charged nanosheets. c 2D negatively charged Ti_0.87O₂ nanosheets with atomic Ti vacancies offer strong electrostatic interaction with Li⁺/Na⁺ ions, resulting in homogeneous distribution of Li⁺/Na⁺-ion flux, preventing the growth of Li/Na dendrites. d 2D negatively charged Ti_0.87O₂ nanosheets with a high negative charge density provide a strong electrostatic repulsion of PS anions, resulting in effective suppression of PS shuttling.