Charged two-dimensional nanochannels with high ion density enabling ultrafast monovalent and multivalent ion conductivity.

Ion conductors with fast ion transport and reliable stability are highly desired for energy storage and conversion devices. While solid-state ion conductors with high safety and energy density are promising materials for a new generation of electrochemical devices, it remains challenging to achieve high ion conductivity, especially for multivalent ions due to the stronger steric effect and electrostatic interactions. Here, we report the well-ordered charged nanochannels with high ion density, typically fabricated by stacking montmorillonite (MMT) nanosheets, to serve as versatile solid-state ion conductors. Characterization studies and molecular dynamics simulations reveal that the "adaptive" nanochannel height of MMT membranes, combined with Coulomb interaction-induced concerted ion movement and surface-charge-governed ion transport arising from the high-packing-density cations inside the negatively charged nanochannels, jointly suppress the steric effect and strong interactions for various cations. As a result, our MMT nanochannels achieve considerably high conductivity for both monovalent (K+, Na+, and Li+) and multivalent ions (Mg2+ and Al3+), ∼80 to 210 mS cm-1 at 80 °C, higher than that of the corresponding bulk solutions and state-of-the-art ion conductors. This work provides fresh perspectives on fast ion transport in nanoconfined environments, and presents a promising route for developing next-generation ionic devices.