3D π-d Conjugated Coordination Polymer Enabling Ultralong Life Magnesium-Ion Storage.

There has been increasing interests in π-d conjugated coordination polymers (CCPs) for energy storage because of their rapid charge transfer through long-range planar π-d conjugation between ligands and metal centers. Nevertheless, currently reported CCPs for energy storage are mostly based on 1D or 2D structures. There are few 3D CCPs reported to date because of the great challenge in constructing nonplanar coordination geometries, let alone their applications in multivalent ions storage. Herein, a triphenylene-catecholate-based 3D CCP (Mn-HHTP) is successfully synthesized assembled from the multidentate chelating groups of hexahydroxytriphenylene (HHTP) ligands and their isotropic coordination with Mn2+ ions. The 3D conjugated structure of Mn-HHTP enables an exceptional cycle life of >4000 cycles at 0.5 A g-1 for multivalent Mg2+ ion storage, which is far superior to most organic and inorganic electrode materials. Experimental characterizations combined with theoretical calculations indicate that the semiquinone radicals at the HHTP ligands are the electroactive centers for Mg2+ ions storage. The excellent performance of Mn-HHTP opens a new avenue towards the design of 3D CCPs for long-life rechargeable magnesium-ion batteries.

Dimensionally Stable Polyimide Frameworks Enabling Long-Life Electrochemical Alkali-Ion Storage.

Organic electrode materials hold unique advantages for electrochemical alkali-ion storage but cannot yet fulfill their potential. The key lies in the design of structurally stable candidates that have negligible solution solubility and can withstand thousands of cycles under operation. To this end, we demonstrate here the preparation of dimensionally stable polyimide frameworks from the two-dimensional cross-linking of tetraaminobenzene and dianhydride. The product consists of hierarchically assembled nanosheets with thin thickness and abundant porosity. Its robust molecular frameworks and advantageous nanoscale features render our polymeric material a promising cathode candidate for both sodium-ion and potassium-ion batteries. Most strikingly, an extraordinary cycle life of up to 6000 cycles at 2 A g-1 is demonstrated, outperforming most of its competitors. Theoretical simulations support the great activity of our polymeric product for the electrochemical alkali-ion storage.

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.