Polyolefin-Based Janus Separator for Rechargeable Sodium Batteries.

Rechargeable sodium battery is a promising technology for low-cost energy storage. However, the undesirable drawbacks originating from the glass fiber membrane separators have been long overlooked. Herein, we report a versatile "grafting-filtrating" strategy to controllably tune commercial polyolefin separators for sodium batteries. The as-developed Janus separators contain a single sodium-ion conducting polymer grafted side and a functional low-dimensional material coated side. When employed in room-temperature sodium-sulfur batteries as an example, a poly(1-[3-(methacryloyloxy) propylsulfonyl]-1-(trifluoromethanesulfonyl)-imide sodium) grafted side effectively enhances the electrolyte wettability, and inhibits the polysulfide diffusion and sodium dendrite growth. Moreover, a titanium-deficient nitrogen-containing MXene coated side electrocatalytically improve the polysulfide conversion kinetics. The as-developed batteries show high capacity, extended cycling life with lean electrolyte loading.