Flexible yet Robust Framework of Tin(II) Oxide Carbodiimide for Reversible Lithium Storage.

Metal-organic frameworks (MOFs) can become promising electrode materials for advanced lithium-ion batteries (LIBs), because their loosely-packed porous structures may mitigate volume expansion and metal atom aggregation which occur to the respective metal oxides. However, they suffer from poor electrical conductivity and irreversible structural degradation upon charge/discharge processes, which impede their practical utilization. Herein, we investigate MOF-like Sn2O(CN2) as a new electrode material. The conductive yet flexible [N=C=N] linkers are tilted between [Sn4O] nodes and cross-linked into a porous quasi-layered structure. Such structure offers abundant channels for fast Li-ion transport and tolerance of enormous volume expansion. Notably, anisotropic [N=C=N]2- arrays hardly migrate so that Sn0 nanodots are physically separated via robust [N=C=N]2- framework during discharge process, thereby effectively preventing the formation of large Sn islands. Owing to the structural advantage, the Sn2O(CN2) electrode exhibits high initial Coulombic efficiency as ~80%. With the addition of graphite as conductive supporter, the electrode provides 978 mA h g-1 at 1.0 A g-1 even after 300 cycles. Such MOF-like carbodiimides hold potential for the advanced electrodes in LIBs and other battery systems.