2D Molecular Sheets of Hydrogen-Bonded Organic Frameworks for Ultrastable Sodium-Ion Storage

There has been growing research interest in hydrogen bonded organic frameworks (HOFs) by virtue of their great structural crystallinity, large surface areas and porosity. Their potential in electrochemical applications, unfortunately, remains elusive because weak hydrogen bonds would dissociate in solution that eventually compromises the structural integrity. Herein, it is demonstrated that this issue may be overcome by designing and introducing multisite hydrogen bonding within HOFs. 2D molecular sheets are prepared using diaminotriazole as the linkers for the first time. In spite of the molecular thickness (≈1 nm), they are chemically stable and mechanically robust, and have diminished solubility in most polar or nonpolar organic solvents. This solution-stable HOF exhibits an excellent electrochemical performance for Na⁺ ion storage. In particular, it enables an exceptional cycle life of >10 000 cycles at 1 A g^-1 , which is far superior to most other organic electrode materials. Theoretical simulations indicate that the activation barrier for the intralayer or interlayer diffusion of Na⁺ ions within the organic frameworks is small.