Flexible yet Robust Framework of Tin(II) Oxide Carbodiimide for Reversible Lithium Storage
Graphical Linked by MOFs : Sn 2 O(CN 2 ) with loosely packed crystal structure possesses a metal–organic framework-like porous framework, which mitigates volume expansion and Sn atom aggregation. Sn 2 O(CN 2 ) shows a significantly enhanced lithium storage performance compared to traditional tin oxide. 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 at 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 Sn 2 O(CN 2 ) as a new electrode material. The conductive yet flexible [N=C=N] linkers are tilted between [Sn 4 O] 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 Sn 0 nanodots are physically separated via robust [N=C=N] 2− framework during discharge, thereby effectively preventing the formation of large Sn islands. Owing to the structural advantage, the Sn 2 O(CN 2 ) electrode exhibits an initial Coulombic efficiency as high as ∼80 %. With the addition of graphite as conductive supporter, the electrode provides 978 mAh 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.
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