1D/2D composite subnanometer channels for ion transport: The role of confined water

As a mass transport media, water is an alternative of organic solvent applied in rechargeable batteries, due to its unique properties, including fast ionic migration, easy-processibility, economic/environmental friendliness, and flame retardancy. However, due to the high activity of water molecules in aqueous electrolytes, the corrosion of metal anode, side reactions, and inferior metal electrodeposition behavior leads to unstable cycling performance, poor Coulombic efficiency (CE), and early-staged failure of batteries. Despite several attempts to regulate the activity of water, migration of ions is sacrificed, due to the limited methods to control the water states. Herein, we developed a subnanoscale confinement strategy based on a nacre-like structure to modulate the activity of water in the solid electrolytes. By tuning the ratio between the two-dimensional (2D) vermiculite and one-dimensional (1D) cellulose nanofibers (CNFs), the capillary size in the 1D/2D structure is altered to achieve a fast Zn²⁺ transport. Our dielectric relaxation and molecular dynamics studies indicate that the enhanced Zn²⁺ conductivity is attributed to the fast water relaxation in the precisely defined 1D/2D capillary. Taking advantage of the regulated activity of the confined water in 2D capillary, the composite vermiculite membrane can suppress the corrosion and side reactions between Zn electrode and water molecular, endowing a reversible Zn²⁺ stripping/plating behavior and a stable cycling performance for 900 h. Based on our confinement strategy to control the water states by 1D/2D structures, this work will open an avenue toward aqueous energy storage devices with excellent reversibility, high safety, and long-term stability.